Switching power supply device

The present invention relates to a switching power supply device.

Research and development of power supply devices have been carried out.

In this regard, a power supply device including a power factor correction circuit is known (see Japanese Unexamined Patent Application, First Publication No. 2012-070490 and Japanese Unexamined Patent Application, Second Publication No. 2001-218467). Particularly, Japanese Unexamined Patent Application, First Publication No. 2012-070490 discloses a power supply device including a totem pole type bridgeless power factor correction converter.

In a switching power supply device in which a totem pole type bridgeless power factor correction converter and an insulation type direct current (DC)-DC converter are combined, conduction noise may be caused on the basis of a noise current which is generated between a primary coil of a transformer of the DC-DC converter and a secondary coil of the transformer may be.

The invention is made in consideration of the above-mentioned circumstances and an objective thereof is to provide a switching power supply device that can curb generation of conduction noise based on a noise current which is generated between a primary coil and a secondary coil of a transformer.

According to an aspect of the invention, there is provided a switching power supply device that is connected to a load and supplies a direct current (DC) voltage to the load, the switching power supply device including: an alternating current (AC) voltage input unit that is supplied with an AC voltage; a filter that is connected to the AC voltage input unit and a frame ground and reduces noise of the AC voltage supplied from the AC voltage input unit; a first inductor that is electrically connected to a first output terminal of the AC voltage input unit via the filter; a switching unit that includes a first switching element and a second switching element, in which the first switching element and the second switching element are connected in series to each other, and of which a terminal which is not electrically connected to the first output terminal of the AC voltage input unit out of two terminals of the first inductor is connected to a transmission line connecting the first switching element and the second switching element; a first rectification unit that includes a first rectifier element and a second rectifier element, in which the first rectifier element and the second rectifier element are connected in series, in which a second output terminal of the AC voltage input unit is electrically connected to a transmission line connecting the first rectifier element and the second rectifier element via the filter, and which is connected in parallel to the switching unit; a first capacitor that is connected in parallel to the first rectification unit; an inverter that includes a transformer including a primary coil and a secondary coil and in which the first capacitor is connected between input terminals thereof; a second rectification unit that includes an input terminal which is connected to the secondary coil; a smoothing unit that is connected between the first and second output terminals of the second rectification unit; a control unit that performs switching control of the first switching element, the second switching element, and a switching element of the inverter; a second capacitor that is connected between a transmission line connecting the first rectifier element and the second rectifier element and the smoothing unit; and a twentieth capacitor that is connected between the smoothing unit and the frame ground.

According to the invention, it is possible to curb generation of conduction noise based on a noise current which is generated between a primary coil and a secondary coil of a transformer.

FIG. 1 is a diagram illustrating an example of a configuration of a switching power supply device 1 according to an embodiment;

FIG. 2 is a diagram illustrating an example of a configuration of the switching power supply device 1 when conduction noise of the switching power supply device 1 is measured;

FIG. 3 is a diagram illustrating an example of conduction noise which is generated in the switching power supply device 1 when a transmission line EL is not provided and when a transmission line EL is provided;

FIG. 4 is a diagram illustrating an example of a circuit configuration of a smoothing unit 16 A according to Modified Example 1 of the embodiment;

FIG. 5 is a diagram illustrating an example of a circuit configuration of a smoothing unit 16 B according to Modified Example 2 of the embodiment; and

FIG. 6 is a diagram illustrating an example of a circuit configuration of a smoothing unit 16 C according to Modified Example 3 of the embodiment.

Embodiment

Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings. In this embodiment, a conductor that transmits an electrical signal based on DC power or an electrical signal based on AC power is referred to as a transmission line. A transmission line may be a conductor which is printed on a board, a wire which is formed of a conductor in a line shape, or another conductor.

<Outline of Switching Power Supply Device>

First, the outline of a switching power supply device according to an embodiment will be described below. A switching power supply device according to the embodiment is connected to a load and supplies a direct current (DC) voltage to the load. The switching power supply device according to the embodiment includes an alternating current (AC) voltage input unit, a filter, a first inductor, a switching unit, a first rectification unit, a first capacitor, an inverter, a second rectification unit, a smoothing unit, a control unit, a second capacitor, and a twentieth capacitor.

The AC voltage input unit is supplied with an AC voltage. The filter is connected to the AC voltage input unit and a frame ground and reduces noise of the AC voltage which is supplied from the AC voltage input unit.

The first inductor is electrically connected to a first output terminal of the AC voltage input unit via a filter. The switching unit includes a first switching element and a second switching element. In the switching unit, the first switching element and the second switching element are connected in series to each other. In the switching unit, a terminal which is not electrically connected to the first output terminal out of two terminals of the first inductor is connected to a transmission line which connects the first switching element and the second switching element.

The first rectification unit includes a first rectifier element and a second rectifier element. In the first rectification unit, the first rectifier element and the second rectifier element are connected in series. In the first rectification unit, a second output terminal of the AC voltage input unit is electrically connected to a transmission line connecting the first rectifier element and the second rectifier element via the filter. The first rectification unit is connected in parallel to the switching unit. The first capacitor is connected in parallel to the first rectification unit.

The inverter includes a transformer including a primary coil and a secondary coil, and the first capacitor is connected between input terminals thereof. The second rectification unit includes an input terminal which is connected to the secondary coil. The smoothing unit is connected between the first and second output terminals of the second rectification unit. The control unit performs switching control of the first switching element, the second switching element, and a switching element of the inverter.

The second capacitor is connected between a transmission line, which connects the first rectifier element and the second rectifier element, and the smoothing unit. The twentieth capacitor is connected between the smoothing unit and the frame ground.

Accordingly, the switching power supply device according to the embodiment can curb generation of conduction noise based on a noise current which is generated between a primary coil and a secondary coil of a transformer. In the following description, a circuit configuration of the switching power supply device will be described in detail.

<Circuit Configuration of Switching Power Supply Device>

Hereinafter, a circuit configuration of the switching power supply device 1 according to the embodiment will be described with reference to FIG. 1 . FIG. 1 is a diagram illustrating an example of a configuration of the switching power supply device 1 according to the embodiment.

The switching power supply device 1 is an example of the above-mentioned switching power supply device. In the example illustrated in FIG. 1 , the switching power supply device 1 is connected to an AC power source PS. The switching power supply device 1 is also connected to a load LD. The switching power supply device 1 converts an AC voltage supplied from the AC power source PS into a DC voltage. Then, the switching power supply device 1 supplies the converted DC voltage to the load LD.

Here, the AC power source PS is a power source that supplies an AC voltage. The AC power source PS may be any power source as long as it can supply an AC voltage. The AC power source PS includes two terminals including a first terminal PSO 1 and a second terminal PSO 2 .

The load LD is, for example, a circuit or a device that is driven on the basis of a DC voltage which is supplied from the switching power supply device 1 . The load LD includes two terminals including a first terminal LDI 1 and a second terminal LDI 2 .

The switching power supply device 1 includes an AC voltage input unit 11 , a filter 18 , a power factor correction circuit 13 , an inverter 14 , a second rectification unit 15 , a smoothing unit 16 , a control unit 17 , a first capacitor C 1 , a second capacitor C 2 , and a twentieth capacitor CFG. The switching power supply device 1 is used in a state in which it is connected to the AC power source PS and the load LD. The switching power supply device 1 may further include some or all of other circuit elements, other devices, and the like.

The AC voltage input unit 11 is supplied with an AC voltage from the AC power source PS. The AC voltage input unit 11 inputs the AC voltage supplied from the AC power source PS to a circuit in a stage following the AC voltage input unit 11 . In the example illustrated in FIG. 1 , the AC voltage input unit 11 inputs the AC voltage to the filter 18 .

The AC voltage input unit 11 includes two input terminals including a first input terminal 11 I 1 and a second input terminal 11 I 2 . The AC voltage input unit 11 includes two output terminals including a first output terminal 11 O 1 and a second output terminal 11 O 2 . The AC voltage input unit 11 may have a configuration including a frame ground (FG) terminal. Here, an FG terminal may be a terminal which is connected to a frame ground FG illustrated in FIG. 1 . In the example illustrated in FIG. 1 , the frame ground FG is a casing of the switching power supply device 1 . The frame ground FG may be another casing other than the casing of the switching power supply device 1 . The frame ground FG is not limited to a casing and may be an FG pattern that is provided in the switching power supply device 1 .

The first input terminal 11 I 1 is connected to a first terminal PSO 1 of the AC power source PS via a transmission line. Accordingly, the first input terminal 11 I 1 is supplied with an AC voltage from the first terminal PSO 1 . A configuration in which another circuit element or the like is connected between the first input terminal 11 I 1 and the first terminal PSO 1 may be employed.

The second input terminal 11 I 2 is connected to a second terminal PSO 2 of the AC power source PS via a transmission line. Accordingly, the second input terminal 11 I 2 is supplied with an AC voltage from the second terminal PSO 2 . A configuration in which another circuit element or the like is connected between the second input terminal 11 I 2 and the second terminal PSO 2 may be employed.

The AC voltage input unit 11 outputs the AC voltage, which is supplied to the first input terminal 11 I 1 , from the first output terminal 11 O 1 .

The AC voltage input unit 11 outputs the AC voltage, which is supplied to the second input terminal 11 I 2 , from the second output terminal 11 O 2 .

The filter 18 is a noise filter. The filter 18 is connected to the AC voltage input unit 11 and the frame ground FG. The filter 18 is supplied with an AC voltage from the AC voltage input unit 11 . The filter 18 reduces conduction noise which is generated in the switching power supply device 1 such that the conduction noise is not transmitted to the AC power source PS. The filter 18 reduces external conduction noise transmitted from the AC power source PS side such that the external conduction noise is not transmitted in the switching power supply device 1 .

More specifically, in the example illustrated in FIG. 1 , the filter 18 includes two input terminals including a first input terminal 18 I 1 and a second input terminal 18 I 2 . The filter 18 includes two output terminals including a first output terminal 18 O 1 and a second output terminal 18 O 2 .

In the example illustrated in FIG. 1 , the filter 18 includes a common-mode choke coil 18 L 1 , a capacitor 18 X 1 , a tenth capacitor 18 X 2 , an eleventh capacitor 18 Y 1 , and a twelfth capacitor 18 Y 2 . The filter 18 may include another circuit element in addition to the circuit elements. The filter 18 may not include the capacitor 18 X 1 . The filter 18 may be a noise filter having another configuration instead of the noise filter having the configuration illustrated in FIG. 1 .

Here, the first input terminal 18 I 1 is connected to the first output terminal 11 O 1 of the AC voltage input unit 11 via a transmission line. The second input terminal 18 I 2 is connected to the second output terminal 11 O 2 of the AC voltage input unit 11 via a transmission line. The capacitor 18 X 1 is connected between the first input terminal 18 I 1 and the second input terminal 18 I 2 via a transmission line. The switching power supply device 1 may employ a configuration in which another circuit element or the like is provided in a transmission line connecting the first output terminal 11 O 1 and the first input terminal 18 I 1 . The switching power supply device 1 may employ a configuration in which another circuit element or the like is provided in a transmission line connecting the second output terminal 11 O 2 and the second input terminal 18 I 2 .

The common-mode choke coil 18 L 1 includes at least two coils. In the example illustrated in FIG. 1 , the common-mode choke coil 18 L 1 includes a coil 18 C 1 and a coil 18 C 2 as the two coils. A terminal which is connected to the first input terminal 18 I 1 out of terminals of the capacitor 18 X 1 is connected to the coil 18 C 1 via a transmission line. A terminal which is connected to the second input terminal 18 I 2 out of the terminals of the capacitor 18 X 1 is connected to the coil 18 C 2 via a transmission line. That is, the common-mode choke coil 18 L 1 is electrically connected between the first output terminal 11 O 1 of the AC voltage input unit 11 and the second output terminal 11 O 2 of the AC voltage input unit 11 .

The tenth capacitor 18 X 2 is connected between a terminal which is not connected to the capacitor 18 X 1 out of terminals of the coil 18 C 1 and a terminal which is not connected to the capacitor 18 X 1 out of terminals of the coil 18 C 2 via a transmission line. That is, the tenth capacitor 18 X 2 is connected between output terminals of the common-mode choke coil 18 L 1 . A node between the output terminals refers to a node between the terminal which is not connected to the capacitor 18 X 1 out of the terminals of the coil 18 C 1 and the terminal which is not connected to the capacitor 18 X 1 out of the terminals of the coil 18 C 2 .

A terminal which is connected to the coil 18 C 1 out of terminals of the tenth capacitor 18 X 2 is connected to the first output terminal 18 O 1 via a transmission line. The eleventh capacitor 18 Y 1 is connected between a node in a transmission line connecting the terminal which is connected to the coil 18 C 1 out of the terminals of the tenth capacitor 18 X 2 to the first output terminal 18 O 1 and the frame ground FG. The terminal which is connected to the coil 18 C 2 out of the terminals of the tenth capacitor 18 X 2 is connected to the second output terminal 18 O 2 via a transmission line. The twelfth capacitor 18 Y 2 is connected between a node in a transmission line connecting the terminal which is connected to the coil 18 C 2 out of the terminals of the tenth capacitor 18 X 2 to the second output terminal 18 O 2 and the frame ground FG. In the example illustrated in FIG. 1 , the terminal which is not connected to the coil 18 C 1 out of the terminals of the eleventh capacitor 18 Y 1 and the terminal not connected to the coil 18 C 2 out of the terminals of the twelfth capacitor 18 Y 2 are connected to each other via a transmission line, and the transmission line and the frame ground FG are connected to each other. However, the terminal which is not connected to the coil 18 C 1 out of the terminals of the eleventh capacitor 18 Y 1 and the terminal which is not connected to the coil 18 C 2 out of the terminals of the twelfth capacitor 18 Y 2 may not be connected to each other via a transmission line but may be independently connected to the common frame ground FG.

The power factor correction circuit 13 is a totem pole type bridgeless power factor correction converter. The power factor correction circuit 13 includes, for example, a first inductor 13 A, a switching unit 13 B, and a first rectification unit 13 C. The circuit configuration of the power factor correction circuit 13 may have another circuit configuration serving as a totem pole type bridgeless power factor correction converter instead of the circuit configuration illustrated in FIG. 1 .

The power factor correction circuit 13 includes two input terminals including a first input terminal 13 I 1 and a second input terminal 13 I 2 . The power factor correction circuit 13 includes two output terminals including a first output terminal 13 O 1 and a second output terminal 13 O 2 . The switching unit 13 B includes a first switching element S 1 and a second switching element S 2 . The first rectification unit 13 C includes a first rectifier element RC 1 and a second rectifier element RC 2 .

The first input terminal 13 I 1 is connected to the first output terminal 18 O 1 of the filter 18 via a transmission line. Accordingly, the first input terminal 13 I 1 is supplied with an AC voltage from the first output terminal 18 O 1 . The switching power supply device 1 may employ a configuration in which another circuit element or the like is provided in a transmission line connecting the first output terminal 18 O 1 and the first input terminal 13 I 1 .

The second input terminal 13 I 2 is connected to the second output terminal 18 O 2 of the filter 18 via a transmission line. Accordingly, the second input terminal 13 I 2 is supplied with an AC voltage from the second output terminal 18 O 2 . The switching power supply device 1 may employ a configuration in which another circuit element or the like is provided in a transmission line connecting the second output terminal 18 O 2 and the second input terminal 13 I 2 .

One terminal of the first inductor 13 A is connected to the first input terminal 13 I 1 via a transmission line. The other terminal of the first inductor 13 A is connected to the switching unit 13 B via a transmission line. In the switching unit 13 B, the first switching element S 1 and the second switching element S 2 are connected in series. The other terminal of the first inductor 13 A is connected to a transmission line connecting the first switching element S 1 and the second switching element S 2 in the switching unit 13 B via a transmission line.

The first switching element S 1 is, for example, a field effect transistor using gallium nitride as a semiconductor. In FIG. 1 , for the purpose of simplification of the drawing, the first switching element S 1 is illustrated as a rectangle. The first switching element S 1 may be a field effect transistor using another material as a semiconductor. The first switching element S 1 may be another switching element such as a bipolar transistor instead of a field effect transistor.

The second switching element S 2 is, for example, a field effect transistor using gallium nitride as a semiconductor. In FIG. 1 , for the purpose of simplification of the drawing, the second switching element S 2 is illustrated as a rectangle. The second switching element S 2 may be a field effect transistor using another material as a semiconductor. The second switching element S 2 may be another switching element such as a bipolar transistor instead of a field effect transistor.

The source terminal of the first switching element S 1 is connected to the drain terminal of the second switching element S 2 via a transmission line. The first rectification unit 13 C of the power factor correction circuit 13 is connected between the drain terminal of the first switching element S 1 and the source terminal of the second switching element S 2 .

In the power factor correction circuit 13 , the first rectifier element RC 1 and the second rectifier element RC 2 are connected in series via a transmission line.

The first rectifier element RC 1 is, for example, a field effect transistor using silicon as a semiconductor. In FIG. 1 , for the purpose of simplification of the drawing, the first rectifier element RC 1 is illustrated as a rectangle. The first rectifier element RC 1 may be a field effect transistor using another material as a semiconductor. The first rectifier element RC 1 may be another switching element such as a bipolar transistor or another rectifier element such as a diode instead of a field effect transistor.

The second rectifier element RC 2 is, for example, a field effect transistor using silicon as a semiconductor. In FIG. 1 , for the purpose of simplification of the drawing, the second rectifier element RC 2 is illustrated as a rectangle. The second rectifier element RC 2 may be a field effect transistor using another material as a semiconductor. The second rectifier element RC 2 may be another switching element such as a bipolar transistor or another rectifier element such as a diode instead of a field effect transistor.

The source terminal of the first rectifier element RC 1 is connected to the drain terminal of the second rectifier element RC 2 via a transmission line. The drain terminal of the first rectifier element RC 1 is connected to the drain terminal of the first switching element S 1 via a transmission line. The first output terminal 13 O 1 is connected to a transmission line connecting the drain terminal of the first rectifier element RC 1 and the drain terminal of the first switching element S 1 via a transmission line. The source terminal of the second rectifier element RC 2 is connected to the source terminal of the second switching element S 2 via a transmission line. The second output terminal 13 O 2 is connected to a transmission line connecting the source terminal of the second rectifier element RC 2 and the source terminal of the second switching element S 2 via a transmission line.

The first capacitor C 1 is, for example, an electrolytic capacitor. The first capacitor C 1 may be another type of capacitor instead of an electrolytic capacitor.

The first capacitor C 1 includes two terminals including a first terminal C 1 I 1 and a second terminal C 1 I 2 . The first terminal C 1 I 1 is connected to the first output terminal 13 O 1 of the first rectification unit 13 C. The second terminal C 1 I 2 is connected to the second output terminal 13 O 2 of the first rectification unit 13 C via a transmission line. That is, the first capacitor C 1 is connected between the first output terminal 13 O 1 and the second output terminal 13 O 2 .

In this way, in the switching power supply device 1 , the switching unit 13 B and the first rectification unit 13 C are connected in parallel. In the switching power supply device 1 , the first rectification unit 13 C and the first capacitor C 1 are connected in parallel.

The inverter 14 is an inverter including circuits of a primary-side half bridge and a secondary-side center tap which are insulated. The inverter 14 includes two input terminals including a first input terminal 14 I 1 and a second input terminal 14 I 2 . The inverter 14 includes three output terminals including a first output terminal 14 O 1 , a second output terminal 14 O 2 , and a third output terminal 14 O 3 . The inverter 14 includes a capacitor 14 A, a capacitor 14 B, a switching element 14 C, a switching element 14 D, and a transformer T. The transformer T includes a first coil CL 1 and a second coil CL 2 . The inverter 14 may employ another circuit configuration serving as an inverter instead of the circuit configuration illustrated in FIG. 1 . That is, the inverter 14 may be an inverter other than a half bridge converter.

The first input terminal 14 I 1 is connected to a transmission line connecting the first output terminal 13 O 1 of the first rectification unit 13 C and the first terminal C 1 I 1 of the first capacitor C 1 via a transmission line. The second input terminal 14 I 2 is connected to a transmission line connecting the second output terminal 13 O 2 of the first rectification unit 13 C and the second terminal C 1 I 2 of the first capacitor C 1 via a transmission line. That is, the first capacitor C 1 is connected between the input terminals of the inverter 14 . A node between the input terminals is a node between the first input terminal 14 I 1 and the second input terminal 14 I 2 .

In the inverter 14 , the capacitor 14 A and the capacitor 14 B are connected in series via a transmission line between the first input terminal 14 I 1 and the second input terminal 14 I 2 . In the example illustrated in FIG. 1 , the capacitor 14 A and the capacitor 14 B are connected in series in the order of the capacitor 14 A and the capacitor 14 B from the first input terminal 14 I 1 to the second input terminal 14 I 2 .

The capacitor 14 A is, for example, a ceramic capacitor. The capacitor 14 A may be another type of capacitor instead of a ceramic capacitor.

The capacitor 14 B is, for example, a ceramic capacitor. The capacitor 14 B may be another type of capacitor instead of a ceramic capacitor.

The switching element 14 C is, for example, a field effect transistor. The switching element 14 C may be another switching element such as a bipolar transistor instead of a field effect transistor.

The switching element 14 D is, for example, a field effect transistor. The switching element 14 D may be another switching element such as a bipolar transistor instead of a field effect transistor.

The drain terminal of the switching element 14 C is connected to a transmission line connecting the first input terminal 14 I 1 and the capacitor 14 A via a transmission line. The source terminal of the switching element 14 C is connected to the drain terminal of the switching element 14 D via a transmission line. The source terminal of the switching element 14 D is connected to a transmission line connecting the second input terminal 14 I 2 and the capacitor 14 B via a transmission line.

The first coil CL 1 is a primary coil of the transformer T. One terminal of the first coil CL 1 is connected to a transmission line connecting the source terminal of the switching element 14 C and the drain terminal of the switching element 14 D via a transmission line. The other terminal of the first coil CL 1 is connected to a transmission line connecting a terminal which is not connected to the first input terminal 14 I 1 out of the terminals of the capacitor 14 A and a terminal which is not connected to the second input terminal 14 I 2 out of the terminals of the capacitor 14 B via a transmission line.

In the example illustrated in FIG. 1 , the first capacitor C 1 is electrically connected to both ends of the first coil CL 1 by the configuration of the inverter 14 illustrated in FIG. 1 . More specifically, in the inverter 14 , when the switching element 14 C is in an ON state and the switching element 14 D is in an OFF state, the first capacitor C 1 is electrically connected to both ends of the first coil CL 1 via the switching element 14 C and the capacitor 14 B. In the inverter 14 , when the switching element 14 C is in the OFF state and the switching element 14 D is in the ON state, the first capacitor C 1 is electrically connected to both ends of the first coil CL 1 via the switching element 14 D and the capacitor 14 A. Here, the ON state refers to a state in which the drain terminal and the source terminal of a field effect transistor are electrically connected to each other. The OFF state refers to a state in which the drain terminal and the source terminal of a field effect transistor are not electrically connected to each other.

The second coil CL 2 is a secondary coil of the transformer T. In the example illustrated in FIG. 1 , the second coil CL 2 includes two coils including a 2 A-th coil CL 2 A and a 2 B-th coil CL 2 B. More specifically, in the second coil CL 2 , the 2 A-th coil CL 2 A and the 2 B-th coil CL 2 B are connected in series.

A terminal which is not connected to the 2 B-th coil CL 2 B out of two terminals of the 2 A-th coil CL 2 A is connected to the first output terminal 14 O 1 via a transmission line. A terminal which is not connected to the 2 A-th coil CL 2 A out of two terminals of the 2 B-th coil CL 2 B is connected to the second output terminal 14 O 2 via a transmission line. The third output terminal 14 O 3 is connected to a transmission line connecting the 2 A-th coil CL 2 A and the 2 B-th coil CL 2 B via a transmission line.

The second rectification unit 15 includes three input terminals including a first input terminal 15 I 1 and a second input terminal 15 I 2 , and a third input terminal 15 I 3 . The second rectification unit 15 includes two output terminals including a first output terminal 15 O 1 and a second output terminal 15 O 2 . The second rectification unit 15 includes two diodes including a diode D 1 and a diode D 2 .

The first input terminal 15 I 1 is connected to the first output terminal 14 O 1 of the inverter 14 via a transmission line. The second input terminal 15 I 2 is connected to the second output terminal 14 O 2 of the inverter 14 via a transmission line. The third input terminal 15 I 3 is connected to the third output terminal 14 O 3 of the inverter 14 via a transmission line. That is, the second rectification unit 15 includes input terminals connected to the second coil CL 2 .

In the second rectification unit 15 , the first input terminal 15 I 1 is connected to the cathode of the diode D 1 via a transmission line. The second input terminal 15 I 2 is connected to the cathode of the diode D 2 via a transmission line. In the second rectification unit 15 , the third input terminal 15 I 3 is connected to the first output terminal 15 O 1 via a transmission line. The anode of the diode D 1 is connected to the anode of the diode D 2 via a transmission line. That is, in the second rectification unit 15 , the diode D 1 and the diode D 2 are connected in series. The second output terminal 15 O 2 is connected to a transmission line connecting the diode D 1 and the diode D 2 via a transmission line.

The first output terminal 15 O 1 of the second rectification unit 15 is a terminal that is electrically connected to a positive terminal of the load LD. The second output terminal 15 O 2 of the second rectification unit 15 is a terminal that is electrically connected to a negative terminal of the load LD.

According to this configuration, the second rectification unit 15 performs full-wave rectification of an AC voltage output from the inverter 14 to a pulsating voltage. The second rectification unit 15 may employ another circuit configuration serving as a circuit that rectifies an AC voltage output from the inverter 14 to a pulsating voltage instead of the circuit configuration illustrated in FIG. 1 .

The smoothing unit 16 performs smoothing of a pulsating voltage having been subjected to full-wave rectification by the second rectification unit 15 and outputs a stable DC voltage. In the example illustrated in FIG. 1 , the smoothing unit 16 includes a third capacitor C 3 . That is, in this example, the third capacitor C 3 is a smoothing capacitor. The smoothing unit 16 may have another circuit configuration serving as a circuit that performs smoothing of a pulsating voltage having been subjected to full-wave rectification by the second rectification unit 15 and outputs a stable DC voltage.

The third capacitor C 3 is, for example, an electrolytic capacitor. The third capacitor C 3 may be another type of capacitor instead of an electrolyte capacitor. One terminal of the third capacitor C 3 is connected to the first output terminal 15 O 1 of the second rectification unit 15 via a transmission line. The other terminal of the third capacitor C 3 is connected to the second output terminal 15 O 2 of the second rectification unit 15 via a transmission line. That is, the smoothing unit 16 is connected between the output terminals of the second rectification unit 15 .

The load LD is connected to both ends of the third capacitor C 3 via a transmission line. Specifically, a first terminal LDI 1 of the load LD is connected to a transmission line connecting the first output terminal 15 O 1 of the second rectification unit 15 and the third capacitor C 3 . A second terminal LDI 2 of the load LD is connected to a transmission line connecting the second output terminal 15 O 2 of the second rectification unit 15 and the third capacitor C 3 . The smoothing unit 16 inputs (supplies) a DC voltage subjected to smoothing to the load LD.

Here, the twentieth capacitor CFG is connected between the smoothing unit 16 and the frame ground FG via a transmission line. In the example illustrated in FIG. 1 , the twentieth capacitor CFG is connected between the terminal which is connected to the second output terminal 15 O 2 of the second rectification unit 15 out of the terminals of the third capacitor C 3 and the frame ground FG. The twentieth capacitor CFG may be connected between another position of the smoothing unit 16 and the frame ground FG. For example, the twentieth capacitor CFG may be connected between the terminal which is connected to the first output terminal 15 O 1 of the second rectification unit 15 out of the terminals of the third capacitor C 3 and the frame ground FG.

The second capacitor C 2 is a capacitor for curbing generation of conduction noise based on a noise current which is generated between the first coil CL 1 on the primary side of the transformer T and the second coil CL 2 on the secondary side of the transformer T. Capacitance of the second capacitor C 2 is much greater than parasitic capacitance between the first coil CL 1 and the second coil CL 2 . This is for curbing generation of conduction noise based on a noise current which is generated between the first coil CL 1 on the primary side of the transformer T and the second coil CL 2 on the secondary side of the transformer T. Here, the second capacitor C 2 is, for example, a ceramic capacitor. The second capacitor C 2 may be another type of capacitor instead of a ceramic capacitor.

The second capacitor C 2 is connected between a transmission line between the rectifier elements and the smoothing unit 16 via a transmission line. Here, the transmission line between the rectifier elements is a transmission line connecting the source terminal of the first rectifier element RC 1 and the drain terminal of the second rectifier element RC 2 . In the example illustrated in FIG. 1 , the second capacitor C 2 is connected between the transmission line between the rectifier elements and the terminal which is connected to the first output terminal 15 O 1 of the second rectification unit 15 out of the terminals of the third capacitor C 3 . The second capacitor C 2 may be connected between the transmission line between the rectifier elements and the terminal which is connected to the second output terminal 15 O 2 of the second rectification unit 15 out of the terminals of the third capacitor C 3 . In the following description, for the purpose of convenience of explanation, the transmission line that connects the transmission line between the rectifier elements and the smoothing unit 16 and that is provided with the second capacitor C 2 is referred to as a transmission line EL.

In this way, in the switching power supply device 1 , the transmission line between the rectifier elements and the smoothing unit 16 are connected to each other via the transmission line EL. Accordingly, in the switching power supply device 1 , a noise current which is generated between the first coil CL 1 of the transformer T and the second coil CL 2 of the transformer T flows to the first coil CL 1 sequentially through the transmission line EL and the first rectification unit 13 C. As a result, with the switching power supply device 1 , it is possible to curb generation of the conduction noise in comparison with a case in which generation of conduction noise based on the noise current is curbed by only the filter 18 .

Here, it is preferable that the second capacitor C 2 be connected between the transmission line between the rectifier elements and a position at which a DC voltage smoothed by the smoothing unit 16 is stabilized out of positions on the transmission line subsequent to the smoothing unit 16 . In this embodiment, the transmission line subsequent to the smoothing unit 16 is a transmission line in a stage following two input terminals of the smoothing unit 16 . The position of the transmission line connecting the first output terminal 15 O 1 of the second rectification unit 15 and the third capacitor C 3 or the position on the transmission line connecting the second output terminal 15 O 2 of the second rectification unit 15 and the third capacitor C 3 is an example of a position at which a DC voltage smoothed by the smoothing unit 16 is stabilized out of positions on the transmission line subsequent to the smoothing unit 16 .

It is preferable that a position on the smoothing unit 16 which is connected to the transmission line EL be close to the second coil CL 2 . This is because generation of conduction noise based on the noise current is empirically most curbed. Accordingly, in the example illustrated in FIG. 1 , the transmission line EL is connected to the terminal which is connected to the first output terminal 15 O 1 of the second rectification unit 15 out of the terminals of the third capacitor C 3 in the smoothing unit 16 .

The switching power supply device 1 may employ a configuration in which a circuit element such as a resistor is connected in series to the second capacitor C 2 on the transmission line EL or may employ a configuration in which a ferrite bead that converts high-frequency noise into heat is provided on the transmission line EL. The second capacitor C 2 may include a plurality of capacitors which are connected in series.

The control unit 17 is, for example, a central processing unit (CPU). The control unit 17 may be another control circuit such as a field programmable gate array (FPGA), an analog integrated circuit, or an analog-digital mixed integrated circuit instead of a CPU.

The control unit 17 performs switching control of the first switching element S 1 , the second switching element S 2 , the first rectifier element RC 1 , the second rectifier element RC 2 , the switching element 14 C of the inverter 14 , and the switching element 14 D of the inverter 14 .

For example, the control unit 17 alternately switches the state of the first rectifier element RC 1 and the state of the second rectifier element RC 2 between an ON state and an OFF state.

That is, when the state of the first rectifier element RC 1 is set to the ON state, the control unit 17 switches the state of the second rectifier element RC 2 to the OFF state. When the state of the first rectifier element RC 1 is set to the OFF state, the control unit 17 switches the state of the second rectifier element RC 2 to the ON state. When the potential of the first terminal PSO 1 of the AC power source PS is higher than the potential of the second terminal PSO 2 of the AC power source PS, the control unit 17 switches the state of the first rectifier element RC 1 to the OFF state and switches the state of the second rectifier element RC 2 to the ON state. When the potential of the first terminal PSO 1 of the AC power source PS is lower than the potential of the second terminal PSO 2 of the AC power source PS, the control unit 17 switches the state of the first rectifier element RC 1 to the ON state and switches the state of the second rectifier element RC 2 to the OFF state. In this way, the control unit 17 performs switching of the state of the first rectifier element RC 1 and the state of the second rectifier element RC 2 at the same frequency as a power supply frequency of the AC power source PS. The power supply frequency is, for example, 50 Hz but is not limited thereto.

For example, the control unit 17 alternately switches the state of the first switching element S 1 and the state of the second switching element S 2 between an ON state and an OFF state. That is, when the state of the first switching element S 1 is the ON state, the control unit 17 switches the state of the second switching element S 2 to the OFF state. When the state of the first switching element S 1 is set the OFF state, the control unit 17 switches the state of the second switching element S 2 to the ON state. The control unit 17 performs switching of the state of the first switching element S 1 and the state of the second switching element S 2 at a frequency higher than the power supply frequency. The control unit 17 performs switching of the state of the first switching element S 1 and the state of the second switching element S 2 , for example, at 100 kHz.

The control unit 17 detects a current flowing in the first inductor 13 A, a voltage across the first capacitor C 1 , and a voltage between the input terminals of the AC voltage input unit 11 (a voltage between the first input terminal 11 I 1 and the second input terminal 11 I 2 or a voltage between the first output terminal 11 O 1 and the second output terminal 11 O 2 ), performs switching of the state of the first switching element S 1 and the state of the second switching element S 2 by pulse width modulation (PWM) control, controls a time ratio of the PWM control such that the current flowing in the first inductor 13 A and the voltage between the input terminals are similar, and controls the voltage across the first capacitor C 1 such that it is a constant voltage (for example, 400 V). Accordingly, the power factor correction circuit 13 performs a power factor correction operation.

When the potential of the first terminal PSO 1 of the AC power source PS is higher than the potential of the second terminal PSO 2 of the AC power source PS, the control unit 17 sets the second switching element S 2 as a control target of the time ratio of the ON state of the PWM control and switches the state of the first switching element S 1 to the ON state when the state of the second switching element S 2 is set to the OFF state by the PWM control. When the potential of the first terminal PSO 1 of the AC power source PS is lower than the potential of the second terminal PSO 2 of the AC power source PS, the control unit 17 sets the first switching element S 1 as a control target of the time ratio of the ON state of the PWM control and switches the state of the second switching element S 2 to the ON state when the state of the first switching element S 1 is set to the OFF state by the PWM control. In this way, the control unit 17 performs switching of the control target of the time ratio of the ON state of the PWM control at the same frequency as the power supply frequency of the AC power source PS. Details of the PWM control method and the control method for power factor correction are known and thus description thereof will be omitted.

For example, the control unit 17 alternately switches the state of the switching element 14 C and the state of the switching element 14 D between an ON state and an OFF state. That is, when the state of the switching element 14 C is set to the ON state, the control unit 17 switches the state of the switching element 14 D to the OFF state. When the state of the switching element 14 C is set to the OFF state, the control unit 17 switches the state of the switching element 14 D to the ON state. The inverter 14 carries out LLC resonance using leakage inductance of the transformer T, excitation inductance of the transformer T, and the capacitors 14 A and 14 B. The control unit 17 controls the switching frequency of the states of the switching element 14 C and the switching element 14 D such that the voltage between the output terminals (the voltage between the first terminal LDI 1 of the load LD and the second terminal LDI 2 of the load LD) is constant by pulse frequency modulation (PFM) control. Details of the PFM control method of an LLC resonance converter (a circuit in which the second rectification unit 15 is combined into the inverter 14 ) are known and thus description thereof will be omitted.

In FIG. 1 , for the purpose of simplification of the drawing, transmission lines connecting the gate terminals of the first switching element S 1 , the second switching element S 2 , the first rectifier element RC 1 , the second rectifier element RC 2 , the switching element 14 C, and the switching element 14 D to the control unit 17 are not illustrated. The control unit 17 performs switching control of the first switching element S 1 , the second switching element S 2 , the first rectifier element RC 1 , the second rectifier element RC 2 , the switching element 14 C, and the switching element 14 D by supplying a voltage to the gate terminals of the first switching element S 1 , the second switching element S 2 , the first rectifier element RC 1 , the second rectifier element RC 2 , the switching element 14 C, and the switching element 14 D. In FIG. 1 , for the purpose of simplification of the drawing, a current detecting circuit that detects a current flowing in the first inductor 13 A and voltage detecting circuits that detect a voltage across the first capacitor C 1 , a voltage across the third capacitor C 3 (a voltage between the output terminals (the voltage between the first terminal LDI 1 of the load LD and the second terminal LDI 2 of the load LD)), and a voltage between the input terminals of the AC voltage input unit 11 (the voltage between the first output terminal 11 O 1 and the second output terminal 11 O 2 ) are also not illustrated.

According to the above-mentioned circuit configuration, in the switching power supply device 1 , a noise current which is generated between the first coil CL 1 of the transformer T and the second coil CL 2 of the transformer T flows to the first coil CL 1 sequentially through the transmission line EL and the first rectification unit 13 C. As a result, with the switching power supply device 1 , it is possible to curb generation of conduction noise based on the noise current.

The configuration of the switching power supply device 1 when conduction noise in the switching power supply device 1 is measured will be described below. FIG. 2 is a diagram illustrating an example of the configuration of the switching power supply device 1 when conduction noise in the switching power supply device 1 is measured. The configuration of the switching power supply device 1 illustrated in FIG. 2 is obtained by adding a line impedance stabilization network (LISN) 12 between the AC power source PS and the AC voltage input unit 11 in the configuration of the switching power supply device 1 illustrated in FIG. 1 .

The LISN 12 is a line impedance stabilization network. The LISN 12 performs stabilization of impedance of power supply lines in the switching power supply device 1 . Accordingly, the LISN 12 enables detection of conduction noise which flows between the AC power source PS and the AC voltage input unit 11 . The LISN 12 may have an existing configuration or may have a configuration which will be developed from now on, as long as it can perform stabilization of impedance in the power supply lines.

The LISN 12 includes two input terminals including a first input terminal 12 I 1 and a second input terminal 12 I 2 . The LISN 12 includes two output terminals including a first output terminal 12 O 1 and a second output terminal 12 O 2 . The LISN 12 further includes an FG terminal 12 O 3 .

In the example illustrated in FIG. 2 , the first input terminal 12 I 1 is connected to the first terminal PSO 1 of the AC power source PS via a transmission line. In the example, the second input terminal 12 I 2 is connected to the second terminal PSO 2 of the AC power source PS via a transmission line. The first output terminal 12 O 1 is connected to the first input terminal 11 I 1 of the AC voltage input unit 11 via a transmission line. The second output terminal 12 O 2 is connected to the second input terminal 11 I 2 of the AC voltage input unit 11 via a transmission line.

The LISN 12 outputs an AC voltage input to the first input terminal 12 I 1 from the first output terminal 12 O 1 . The LISN 12 outputs an AC voltage input to the second input terminal 12 I 2 from the second output terminal 12 O 2 . The frame ground FG is connected to the FG terminal 12 O 3 of the LISN 12 . Here, the twentieth capacitor CFG is connected to the LISN 12 via a transmission line. The twentieth capacitor CFG is electrically connected to the FG terminal 12 O 3 of the LISN 12 . That is, the twentieth capacitor CFG is connected to the frame ground FG via the FG terminal 12 O 3 . In a conduction noise measurement test of the switching power supply device 1 illustrated in FIG. 2 , measurement is performed using an electromagnetic shield space (a shield room).

FIG. 3 is a diagram illustrating an example of conduction noise which is generated in the switching power supply device 1 when the transmission line EL is not provided and when the transmission line EL is provided. FIG. 3 illustrates results of a conduction noise measurement test of the switching power supply device 1 illustrated in FIG. 2 using an electromagnetic shield space. A graph G 1 illustrated in FIG. 3 represents an example of conduction noise which is generated in the switching power supply device 1 when the transmission line EL is not provided. The horizontal axis of the graph G 1 represents a frequency of conduction noise. The vertical axis of the graph G 1 represents a level of conduction noise which is expressed in dB(μV). The line BLv illustrated in the graph G 1 indicates an allowable value which is determined by the standard such as ITE/standard: CISPR32 Class B. That is, it is preferable that the level of conduction noise in the switching power supply device 1 is suppressed to be lower than the line BLv in each frequency band.

On the other hand, a graph G 2 illustrated in FIG. 3 represents an example of conduction noise which is generated in the switching power supply device 1 when the transmission line EL is provided. The horizontal axis of the graph G 2 represents a frequency of conduction noise. The vertical axis of the graph G 2 represents a level of conduction noise which is expressed in dB(μV).

From comparison between the graph G 1 and the graph G 2 , it can be seen that conduction noise which is generated in the switching power supply device 1 can be curbed by providing the transmission line EL in the switching power supply device 1 .

Modified Example 1 of Embodiment

Modified Example 1 of the embodiment will be described below with reference to FIG. 4 . In Modified Example 1 of the embodiment, the same constituent elements as in the embodiment will be referred to by the same reference signs and description thereof will not be repeated. In Modified Example 1 of the embodiment, the switching power supply device 1 includes a smoothing unit 16 A illustrated in FIG. 4 instead of the smoothing unit 16 . FIG. 4 is a diagram illustrating an example of a circuit configuration of the smoothing unit 16 A according to Modified Example 1 of the embodiment.

The smoothing unit 16 A includes a fourth capacitor C 4 , a fifth capacitor C 5 , and a second inductor L 2 .

The fourth capacitor C 4 is, for example, an electrolytic capacitor. The fourth capacitor C 4 may be another type of capacitor instead of an electrolytic capacitor.

The fifth capacitor C 5 is, for example, an electrolytic capacitor. The fifth capacitor C 5 may be another type of capacitor instead of an electrolytic capacitor.

The fourth capacitor C 4 is connected between the output terminals of the second rectification unit 15 via a transmission line. The second inductor L 2 is connected to a terminal which is connected to the first output terminal 15 O 1 of the second rectification unit 15 out of terminals of the fourth capacitor C 4 . The first output terminal 16 AO 1 of the smoothing unit 16 A is connected to a terminal which is not connected to the fourth capacitor C 4 out of terminals of the second inductor L 2 . The second output terminal 16 AO 2 of the smoothing unit 16 A is connected to the terminal which is connected to the second output terminal 15 O 2 of the second rectification unit 15 out of the terminals of the fourth capacitor C 4 . The fifth capacitor C 5 is connected between the output terminals of the smoothing unit 16 A.

In the example illustrated in FIG. 4 , the transmission line EL is connected between the transmission line between the rectifier elements and the terminal which is connected to the first output terminal 15 O 1 of the second rectification unit 15 out of the terminals of the fourth capacitor C 4 . That is, in the example, the second capacitor C 2 is connected between the transmission line between the rectifier elements and the terminal which is connected to the first output terminal 15 O 1 of the second rectification unit 15 out of the terminals of the fourth capacitor C 4 . In the example, the twentieth capacitor CFG is connected between the terminal which is connected to the second output terminal 15 O 2 of the second rectification unit 15 out of the terminals of the fourth capacitor C 4 and the frame ground FG which is not illustrated in FIG. 4 .

According to the above-mentioned circuit configuration, in the switching power supply device 1 according to Modified Example 1 of the embodiment, a noise current which is generated between the first coil CL 1 of the transformer T and the second coil CL 2 of the transformer T flows to the first coil CL 1 sequentially through the transmission line EL and the first rectification unit 13 C. As a result, with the switching power supply device 1 , it is possible to curb generation of conduction noise based on the noise current.

In the switching power supply device 1 according to Modified Example 1 of the embodiment, the second capacitor C 2 may be connected between the transmission line between the rectifier elements and the terminal which is connected to the second output terminal 15 O 2 of the second rectification unit 15 out of the terminals of the fourth capacitor C 4 via a transmission line. In the switching power supply device 1 , the second capacitor C 2 may be connected between the transmission line between the rectifier elements and the terminal which is connected to the first output terminal 15 O 1 of the second rectification unit 15 via the second inductor L 2 out of the terminals of the fifth capacitor C 5 via a transmission line. In the switching power supply device 1 , the second capacitor C 2 may be connected between the transmission line between the rectifier elements and the terminal which is connected to the second output terminal 15 O 2 of the second rectification unit 15 out of the terminals of the fifth capacitor C 5 via a transmission line.

Here, it is preferable that the second capacitor C 2 be connected between the transmission line between the rectifier elements and a position at which a DC voltage smoothed by the smoothing unit 16 A is stabilized out of positions of the transmission line subsequent to the smoothing unit 16 A. In this embodiment, the transmission line subsequent to the smoothing unit 16 A is a transmission line in a stage following two input terminals of the smoothing unit 16 A. One of four terminals including two terminals of the fourth capacitor C 4 and two terminals of the fifth capacitor C 5 is an example of the position at which a DC voltage smoothed by the smoothing unit 16 A is stabilized out of positions on the transmission line subsequent to the smoothing unit 16 A.

It is preferable that a position on the smoothing unit 16 A which is connected to the transmission line EL be close to the second coil CL 2 . This is because generation of conduction noise based on the noise current is empirically most curbed. Accordingly, in the example illustrated in FIG. 4 , the transmission line EL is connected to the terminal which is connected to the first output terminal 15 O 1 of the second rectification unit 15 out of the terminals of the fourth capacitor C 4 in the smoothing unit 16 A.

In the smoothing unit 16 A illustrated in FIG. 4 , the position which is connected to the second inductor L 2 may be a position which is different from the position illustrated in FIG. 4 .

For example, the second inductor L 2 may be connected to the terminal which is connected to the second output terminal 15 O 2 out of the terminals of the fourth capacitor C 4 . In this case, the first output terminal 16 AO 1 of the smoothing unit 16 A is connected to the terminal which is connected to the first output terminal 15 O 1 of the second rectification unit 15 out of the terminals of the fourth capacitor C 4 . In this case, the second output terminal 16 AO 2 of the smoothing unit 16 A is connected to the terminal which is not connected to the fourth capacitor C 4 out of the terminals of the second inductor L 2 . In this case, the fifth capacitor C 5 is connected between the output terminals of the smoothing unit 16 A (that is, between the first output terminal 16 AO 1 and the second output terminal 16 AO 2 ).

Modified Example 2 of Embodiment

Modified Example 2 of the embodiment will be described below with reference to FIG. 5 . In Modified Example 2 of the embodiment, the same constituent elements as in the embodiment will be referred to by the same reference signs and description thereof will not be repeated. In Modified Example 2 of the embodiment, the switching power supply device 1 includes a smoothing unit 16 B illustrated in FIG. 5 instead of the smoothing unit 16 . FIG. 5 is a diagram illustrating an example of a circuit configuration of the smoothing unit 16 B according to Modified Example 2 of the embodiment.

The smoothing unit 16 B includes a sixth capacitor C 6 , a seventh capacitor C 7 , a third inductor L 3 , and a fourth inductor L 4 .

The sixth capacitor C 6 is, for example, an electrolytic capacitor. The sixth capacitor C 6 may be another type of capacitor instead of an electrolytic capacitor.

The seventh capacitor C 7 is, for example, an electrolytic capacitor. The seventh capacitor C 7 may be another type of capacitor instead of an electrolytic capacitor.

The fourth inductor L 4 is connected to the first output terminal 15 O 1 of the second rectification unit 15 . The sixth capacitor C 6 is connected between the terminal which is not connected to the first output terminal 15 O 1 of the second rectification unit 15 out of the terminals of the fourth inductor L 4 and the second output terminal 15 O 2 of the second rectification unit 15 . The third inductor L 3 is connected to the terminal which is connected to the fourth inductor L 4 out of the terminals of the sixth capacitor C 6 . A first output terminal 16 BO 1 of the smoothing unit 16 B is connected to the terminal which is not connected to the sixth capacitor C 6 out of the terminals of the third inductor L 3 . A second output terminal 16 BO 2 of the smoothing unit 16 B is connected to the terminal which is connected to the second output terminal 15 O 2 of the second rectification unit 15 out of the terminals of the sixth capacitor C 6 . The seventh capacitor C 7 is connected between the output terminals of the smoothing unit 16 B.

In the example illustrated in FIG. 5 , the transmission line EL is connected between the transmission line between the rectifier elements and the terminal which is connected to the fourth inductor L 4 out of the terminals of the sixth capacitor C 6 . That is, in the example, the second capacitor C 2 is connected between the transmission line between the rectifier elements and the terminal which is connected to the fourth inductor L 4 out of the terminals of the sixth capacitor C 6 . In the example, the twentieth capacitor CFG is connected between the terminal which is connected to the second output terminal 15 O 2 of the second rectification unit 15 out of the terminals of the sixth capacitor C 6 and the frame ground FG which is not illustrated in FIG. 5 .

According to the above-mentioned circuit configuration, in the switching power supply device 1 according to Modified Example 2 of the embodiment, a noise current which is generated between the first coil CL 1 on the primary side of the transformer T and the second coil CL 2 on the secondary side of the transformer T flows to the first coil CL 1 sequentially through the transmission line EL and the first rectification unit 13 C. As a result, with the switching power supply device 1 , it is possible to curb generation of conduction noise based on the noise current.

In the switching power supply device 1 according to Modified Example 2 of the embodiment, the second capacitor C 2 may be connected between the transmission line between the rectifier elements and the terminal which is connected to the second output terminal 15 O 2 of the second rectification unit 15 out of the terminals of the sixth capacitor C 6 . In the switching power supply device 1 , the second capacitor C 2 may be connected between the transmission line between the rectifier elements and the terminal which is connected to the third inductor L 3 out of the terminals of the seventh capacitor C 7 . In the switching power supply device 1 , the second capacitor C 2 may be connected between the transmission line between the rectifier elements and the terminal which is connected to the second output terminal 15 O 2 of the second rectification unit 15 out of the terminals of the seventh capacitor C 7 .

Here, it is preferable that the second capacitor C 2 be connected between the transmission line between the rectifier elements and a position at which a DC voltage smoothed by the smoothing unit 16 B is stabilized out of positions on the transmission line subsequent to the smoothing unit 16 B. In this embodiment, the transmission line subsequent to the smoothing unit 16 B is a transmission line in a stage following two input terminals of the smoothing unit 16 B. One of four terminals including two terminals of the sixth capacitor C 6 and two terminals of the seventh capacitor C 7 is an example of the position at which a DC voltage smoothed by the smoothing unit 16 B is stabilized out of positions on the transmission line subsequent to the smoothing unit 16 B.

It is preferable that a position on the smoothing unit 16 B which is connected to the transmission line EL be close to the second coil CL 2 . This is because generation of conduction noise based on the noise current is empirically further curbed. Accordingly, in the example illustrated in FIG. 5 , the transmission line EL is connected to the terminal which is connected to the fourth inductor L 4 out of the terminals of the sixth capacitor C 6 in the smoothing unit 16 B.

In the smoothing unit 16 B illustrated in FIG. 5 , the position which is connected to the fourth inductor L 4 may be a position which is different from the position illustrated in FIG. 5 .

For example, the fourth inductor L 4 may be connected to the second output terminal 15 O 2 of the second rectification unit 15 instead of the first output terminal 15 O 1 of the second rectification unit 15 . In this case, the sixth capacitor C 6 is connected to the terminal which is not connected to the second output terminal 15 O 2 of the second rectification unit 15 out of the terminals of the fourth inductor L 4 . In this case, the first output terminal 15 O 1 of the second rectification unit 15 is connected to the terminal which is not connected to the fourth inductor L 4 out of the terminals of the sixth capacitor C 6 . In this case, the third inductor L 3 is connected to the terminal which is connected to the first output terminal 15 O 1 of the second rectification unit 15 out of the terminals of the sixth capacitor C 6 . In this case, the first output terminal 16 BO 1 of the smoothing unit 16 B is connected to the terminal which is not connected to the sixth capacitor C 6 out of the terminals of the third inductor L 3 . In this case, the second output terminal 16 BO 2 of the smoothing unit 16 B is connected to the terminal which is connected to the fourth inductor L 4 out of the terminals of the sixth capacitor C 6 . In this case, the seventh capacitor C 7 is connected between the output terminals of the smoothing unit 16 B.

In the smoothing unit 16 B illustrated in FIG. 5 , the position which is connected to the third inductor L 3 may be a position which is different from the position illustrated in FIG. 5 .

For example, the third inductor L 3 may be connected between the terminal which is connected to the second output terminal 15 O 2 out of the terminals of the sixth capacitor C 6 and the second output terminal 16 BO 2 of the smoothing unit 16 B. In this case, the terminal which is connected to the first output terminal 15 O 1 out of the terminals of the sixth capacitor C 6 is connected to the first output terminal 16 BO 1 of the smoothing unit 16 B. In this case, the seventh capacitor C 7 is connected between the output terminals of the smoothing unit 16 B.

In the smoothing unit 16 B illustrated in FIG. 5 , the positions which is connected to the third inductor L 3 and the fourth inductor L 4 may be positions which are different from the positions illustrated in FIG. 5 .

For example, the fourth inductor L 4 may be connected to the second output terminal 15 O 2 instead of the first output terminal 15 O 1 . The third inductor L 3 may be connected to the terminal which is not connected to the second output terminal 15 O 2 out of the terminals of the fourth inductor L 4 . In this case, the sixth capacitor C 6 is connected between the terminal which is not connected to the second output terminal 15 O 2 of the second rectification unit 15 out of the terminals of the fourth inductor L 4 and the first output terminal 15 O 1 of the second rectification unit 15 . In this case, the first output terminal 16 BO 1 of the smoothing unit 16 B is connected to the terminal which is connected to the first output terminal 15 O 1 of the second rectification unit 15 out of the terminals of the sixth capacitor C 6 . In this case, the second output terminal 16 BO 2 of the smoothing unit 16 B is connected to the terminal which is not connected to the sixth capacitor C 6 out of the terminals of the third inductor L 3 . In this case, the seventh capacitor C 7 is connected between the output terminals of the smoothing unit 16 B.

Modified Example 3 of Embodiment

Modified Example 3 of the embodiment will be described below with reference to FIG. 6 . In Modified Example 3 of the embodiment, the same constituent elements as in the embodiment will be referred to by the same reference signs and description thereof will not be repeated. In Modified Example 3 of the embodiment, the switching power supply device 1 includes a smoothing unit 16 C illustrated in FIG. 6 instead of the smoothing unit 16 . FIG. 6 is a diagram illustrating an example of a circuit configuration of the smoothing unit 16 C according to Modified Example 3 of the embodiment.

The smoothing unit 16 C includes an eighth capacitor C 8 , a ninth capacitor C 9 , a fifth inductor L 5 , and a sixth inductor L 6 .

The eighth capacitor C 8 is, for example, an electrolytic capacitor. The eighth capacitor C 8 may be another type of capacitor instead of an electrolytic capacitor.

The ninth capacitor C 9 is, for example, an electrolytic capacitor. The ninth capacitor C 9 may be another type of capacitor instead of an electrolytic capacitor.

The eighth capacitor C 8 is connected between the output terminals of the second rectification unit 15 . The fifth inductor L 5 is connected to the terminal which is connected to the first output terminal 15 O 1 of the second rectification unit 15 out of the terminals of the eighth capacitor C 8 . The sixth inductor L 6 is connected to the terminal which is connected to the second output terminal 15 O 2 of the second rectification unit 15 out of the terminals of the eighth capacitor C 8 . A first output terminal 16 CO 1 of the smoothing unit 16 C is connected to the terminal which is not connected to the eighth capacitor C 8 out of the terminals of the fifth inductor L 5 . A second output terminal 16 CO 2 of the smoothing unit 16 C is connected to the terminal which is not connected to the eighth capacitor C 8 out of the terminals of the sixth inductor L 6 . The ninth capacitor C 9 is connected between the output terminals of the smoothing unit 16 C.

In the example illustrated in FIG. 6 , the transmission line EL is connected between the transmission line between the rectifier elements and the terminal which is connected to the first output terminal 15 O 1 of the second rectification unit 15 out of the terminals of the eighth capacitor C 8 . That is, in the example, the second capacitor C 2 is connected between the transmission line between the rectifier elements and the terminal which is connected to the first output terminal 15 O 1 of the second rectification unit 15 out of the terminals of the eighth capacitor C 8 . In the example, the twentieth capacitor CFG is connected between the terminal which is connected to the second output terminal 15 O 2 of the second rectification unit 15 out of the terminals of the eighth capacitor C 8 and the frame ground FG which is not illustrated in FIG. 6 .

According to the above-mentioned circuit configuration, in the switching power supply device 1 according to Modified Example 3 of the embodiment, a noise current which is generated between the first coil CL 1 on the primary side of the transformer T and the second coil CL 2 on the secondary side of the transformer T flows to the first coil CL 1 sequentially through the transmission line EL and the first rectification unit 13 C. As a result, with the switching power supply device 1 , it is possible to curb generation of conduction noise based on the noise current.

In the switching power supply device 1 according to Modified Example 3 of the embodiment, the second capacitor C 2 may be connected between the transmission line between the rectifier elements and the terminal which is connected to the second output terminal 15 O 2 of the second rectification unit 15 out of the terminals of the eighth capacitor C 8 . In the switching power supply device 1 , the second capacitor C 2 may be connected between the transmission line between the rectifier elements and the terminal which is connected to the fifth inductor L 5 out of the terminals of the ninth capacitor C 9 . In the switching power supply device 1 , the second capacitor C 2 may be connected between the transmission line between the rectifier elements and the terminal which is connected to the sixth inductor L 6 out of the terminals of the ninth capacitor C 9 .

Here, it is preferable that the second capacitor C 2 be connected between the transmission line between the rectifier elements and a position at which a DC voltage smoothed by the smoothing unit 16 C is stabilized out of positions on the transmission line subsequent to the smoothing unit 16 C. In this embodiment, the transmission line subsequent to the smoothing unit 16 C is a transmission line in a stage following two input terminals of the smoothing unit 16 C. One of four terminals including two terminals of the eighth capacitor C 8 and two terminals of the ninth capacitor C 9 is an example of the position at which a DC voltage smoothed by the smoothing unit 16 C is stabilized out of positions on the transmission line subsequent to the smoothing unit 16 C.

It is preferable that a position on the smoothing unit 16 C which is connected to the transmission line EL be close to the second coil CL 2 . This is because generation of conduction noise based on the noise current is empirically most curbed. Accordingly, in the example illustrated in FIG. 6 , the transmission line EL is connected to the terminal which is connected to the first output terminal 15 O 1 of the second rectification unit 15 out of the terminals of the eighth capacitor C 8 in the smoothing unit 16 C.

Modified Example 4 of Embodiment

Modified Example 4 of the embodiment will be described below. In Modified Example 4 of the embodiment, the same constituent elements as in the embodiment will be referred to by the same reference signs and description thereof will not be repeated. In Modified Example 4 of the embodiment, the switching power supply device 1 includes a first rectifier element RC 1 A instead of the first rectifier element RC 1 . In Modified Example 4 of the embodiment, the switching power supply device 1 includes a second rectifier element RC 2 A instead of the second rectifier element RC 2 .

The first rectifier element RC 1 A is a diode.

The second rectifier element RC 2 A is a diode.

In the switching power supply device 1 Modified Example 4 of the embodiment, the anode of the first rectifier element RC 1 A is connected to the cathode of the second rectifier element RC 2 A. The cathode of the first rectifier element RC 1 A is connected to a transmission line connecting the drain terminal of the first switching element S 1 and the first terminal C 1 I 1 of the first capacitor C 1 . The anode of the second rectifier element RC 2 A is connected to a transmission line connecting the source terminal of the second switching element S 2 and the second terminal C 1 I 2 of the second capacitor C 2 .

In this way, in the switching power supply device 1 , even when the first rectifier element RC 1 A is provided instead of the first rectifier element RC 1 and the second rectifier element RC 2 A is provided instead of the second rectifier element RC 2 , a noise current which is generated between the first coil CL 1 on the primary side of the transformer T and the second coil CL 2 on the secondary side of the transformer T flows to the first coil CL 1 sequentially through the transmission line EL and the first rectification unit 13 C. As a result, with the switching power supply device 1 , it is possible to curb generation of conduction noise based on the noise current.

The switching power supply device 1 according to the embodiment has a simpler circuit configuration than the switching power supply device 1 according to Modified Examples 1 to 3 of the embodiment. Accordingly, in the switching power supply device 1 according to the embodiment, it is possible to suppress an increase in manufacturing cost in comparison with the switching power supply device 1 according to Modified Examples 1 to 3 of the embodiment.

As described above, the switching power supply device according to the embodiment is a switching power supply device that is connected to a load and supplies a DC voltage to the load, the switching power supply device including: an AC voltage input unit that is supplied with an AC voltage; a filter that is connected to the AC voltage input unit and a frame ground and is supplied with the AC voltage from the AC voltage input unit; a first inductor that is electrically connected to a first output terminal of the AC voltage input unit via the filter; a switching unit that includes a first switching element and a second switching element, in which the first switching element and the second switching element are connected in series to each other, and of which a terminal which is not electrically connected to the first output terminal of the AC voltage input unit out of two terminals of the first inductor is connected to a transmission line connecting the first switching element and the second switching element; a first rectification unit that includes a first rectifier element and a second rectifier element, in which the first rectifier element and the second rectifier element are connected in series, in which a second output terminal of the AC voltage input unit is electrically connected to a transmission line connecting the first rectifier element and the second rectifier element via the filter, and that is connected in parallel to the switching unit; a first capacitor that is connected in parallel to the first rectification unit; an inverter that includes a transformer including a primary coil and a secondary coil and in which the first capacitor is connected between input terminals thereof; a second rectification unit that includes an input terminal which is connected to the secondary coil; a smoothing unit that is connected between the first and second output terminals of the second rectification unit; a control unit that performs switching control of the first switching element, the second switching element, and a switching element of the inverter; a second capacitor that is connected between a transmission line connecting the first rectifier element and the second rectifier element and the smoothing unit; and a twentieth capacitor that is connected between the smoothing unit and the frame ground. Accordingly, with the switching power supply device, it is possible to curb generation of conduction noise based on a noise current which is generated between a primary coil and a secondary coil of a transformer.

The switching power supply device may employ a configuration in which the smoothing unit includes a third capacitor that is connected between the first and second output terminals of the second rectification unit, and the second capacitor is connected between a transmission line connecting the first rectifier element and the second rectifier element and one terminal of the third capacitor.

The switching power supply device may employ a configuration in which the smoothing unit includes: a fourth capacitor that is connected between the first and second output terminals of the second rectification unit; a second inductor that is connected to a terminal which is connected to a first output terminal of the second rectification unit out of terminals of the fourth capacitor; a first output terminal of the smoothing unit that is connected to a terminal which is not connected to the fourth capacitor out of terminals of the second inductor; a second output terminal of the smoothing unit that is connected to a terminal which is connected to a second output terminal of the second rectification unit out of the terminals of the fourth capacitor; and a fifth capacitor that is connected between the first and second output terminals of the smoothing unit, and the second capacitor is connected between a transmission line connecting the first rectifier element and the second rectifier element and one of four terminals including both terminals of the fourth capacitor and both terminals of the fifth capacitor.

The switching power supply device may employ a configuration in which the smoothing unit includes: a fourth capacitor that is connected between the first and second output terminals of the second rectification unit; a second inductor that is connected to a terminal which is connected to a second output terminal of the second rectification unit out of terminals of the fourth capacitor; a first output terminal of the smoothing unit that is connected to a terminal which is connected to a first output terminal of the second rectification unit out of the terminals of the fourth capacitor; a second output terminal of the smoothing unit that is connected to a terminal which is not connected to the fourth capacitor out of terminals of the second inductor; and a fifth capacitor that is connected between the first and second output terminals of the smoothing unit, and the second capacitor is connected between a transmission line connecting the first rectifier element and the second rectifier element and one of four terminals including both terminals of the fourth capacitor and both terminals of the fifth capacitor.

The switching power supply device may employ a configuration in which the smoothing unit includes: a fourth inductor that is connected to a first output terminal of the second rectification unit; a sixth capacitor that is connected between a terminal which is not connected to the first output terminal of the second rectification unit out of terminals of the fourth inductor and a second output terminal of the second rectification unit; a third inductor that is connected to a terminal which is connected to the fourth inductor out of terminals of the sixth capacitor; a first output terminal of the smoothing unit that is connected to a terminal which is not connected to the sixth capacitor out of terminals of the third inductor; a second output terminal of the smoothing unit that is connected to a terminal which is connected to the second output terminal of the second rectification unit out of the terminals of the sixth capacitor; and a seventh capacitor that is connected between the first and second output terminals of the smoothing unit, and the second capacitor is connected between a transmission line connecting the first rectifier element and the second rectifier element and one of four terminals including both terminals of the sixth capacitor and both terminals of the seventh capacitor.

The switching power supply device may employ a configuration in which the smoothing unit includes: a fourth inductor that is connected to a second output terminal of the second rectification unit; a sixth capacitor that is connected between a terminal which is not connected to the second output terminal of the second rectification unit out of terminals of the fourth inductor and a first output terminal of the second rectification unit; a third inductor that is connected to a terminal which is connected to the first output terminal of the second rectification unit out of terminals of the sixth capacitor; a first output terminal of the smoothing unit that is connected to a terminal which is not connected to the sixth capacitor out of terminals of the third inductor; a second output terminal of the smoothing unit that is connected to a terminal which is connected to the fourth inductor out of the terminals of the sixth capacitor; and a seventh capacitor that is connected between the first and second output terminals of the smoothing unit, and the second capacitor is connected between a transmission line connecting the first rectifier element and the second rectifier element and one of four terminals including both terminals of the sixth capacitor and both terminals of the seventh capacitor.

The switching power supply device may employ a configuration in which the smoothing unit includes: a fourth inductor that is connected to a first output terminal of the second rectification unit; a sixth capacitor that is connected between a terminal which is not connected to the first output terminal of the second rectification unit out of terminals of the fourth inductor and a second output terminal of the second rectification unit; a third inductor that is connected to a terminal which is connected to the second output terminal of the second rectification unit out of terminals of the sixth capacitor; a first output terminal of the smoothing unit that is connected to a terminal connected to the fourth inductor out of terminals of the sixth capacitor; a second output terminal of the smoothing unit that is connected to a terminal not connected to the sixth capacitor out of terminals of the third inductor; and a seventh capacitor that is connected between the first and second output terminals of the smoothing unit, and the second capacitor is connected between a transmission line connecting the first rectifier element and the second rectifier element and one of four terminals including both terminals of the sixth capacitor and both terminals of the seventh capacitor.

The switching power supply device may employ a configuration in which the smoothing unit includes: a fourth inductor that is connected to a second output terminal of the second rectification unit; a sixth capacitor that is connected between a terminal which is not connected to the second output terminal of the second rectification unit out of terminals of the fourth inductor and a first output terminal of the second rectification unit; a third inductor that is connected to a terminal which is connected to the fourth inductor out of terminals of the sixth capacitor; a first output terminal of the smoothing unit that is connected to a terminal connected to the first output terminal of the second rectification unit out of terminals of the sixth capacitor; a second output terminal of the smoothing unit that is connected to a terminal which is not connected to the sixth capacitor out of the terminals of the third inductor; and a seventh capacitor that is connected between the first and second output terminals of the smoothing unit, and the second capacitor is connected between a transmission line connecting the first rectifier element and the second rectifier element and one of four terminals including both terminals of the sixth capacitor and both terminals of the seventh capacitor.

The switching power supply device may employ a configuration in which the smoothing unit includes: an eighth capacitor that is connected between the first and second output terminals of the second rectification unit; a fifth inductor that is connected to a terminal which is connected to a first output terminal of the second rectification unit out of terminals of the eighth capacitor; a sixth inductor that is connected to a terminal which is connected to a second output terminal of the second rectification unit out of the terminals of the eighth capacitor; a first output terminal of the smoothing unit that is connected to a terminal which is not connected to the eighth capacitor out of terminals of the fifth inductor; a second output terminal of the smoothing unit that is connected to a terminal which is not connected to the eighth capacitor out of terminals of the sixth inductor; and a ninth capacitor that is connected between the first and second output terminals of the smoothing unit, and the second capacitor is connected between a transmission line connecting the first rectifier element and the second rectifier element and one of four terminals including both terminals of the eighth capacitor and both terminals of the ninth capacitor.

The switching power supply device may employ a configuration in which the first rectifier element and the second rectifier element are switching elements, and the control unit performs switching control of the first switching element, the second switching element, and a switching element of the inverter and performs switching control of the first rectifier element and the second rectifier element.

While an embodiment of the invention has been described above in detail with reference to the drawings, a specific configuration of the invention is not limited to the embodiment and may be modified, replaced, or deleted without departing from the gist of the invention.

1 Switching power supply device

11 AC voltage input unit

13 Power factor correction circuit

13 A First inductor

13 B Switching unit

13 C First rectification unit

14 Inverter

14 A, 14 B Capacitor

14 C, 14 D Switching element

15 Second rectification unit

16 , 16 A, 16 B, 16 C Smoothing unit

17 Control unit

18 Filter

18 C 1 , 18 C 2 Coil

18 L 1 Common-mode choke coil

18 X 1 Capacitor

18 X 2 Tenth capacitor

18 Y 1 Eleventh capacitor

18 Y 2 Twelfth capacitor

C 1 First capacitor

C 2 Second capacitor

C 3 Third capacitor

C 4 Fourth capacitor

C 5 Fifth capacitor

C 6 Sixth capacitor

C 7 Seventh capacitor

C 8 Eighth capacitor

C 9 Ninth capacitor

CFG Twentieth capacitor

CL 1 First coil

CL 2 Second coil

CL 2 A 2 A-th coil

CL 2 B 2 B-th coil

D 1 , D 2 Diode

EL Transmission line

L 2 Second inductor

L 3 Third inductor

L 4 Fourth inductor

L 5 Fifth inductor

L 6 Sixth inductor

LD Load

PS AC power source

RC 1 First rectifier element

RC 1 A first rectifier element

RC 2 Second rectifier element

RC 2 A Second rectifier element

S 1 First switching element

S 2 Second switching element

T Transformer