Synchronous rectifier driving method, synchronous rectifier circuit and switching power supply

Embodiments of the present disclosure relate to, but is not limited to, a switching power supply field, in particular to a synchronous rectifier driving method, a synchronous rectifier circuit and a switching power supply.

In order to meet the requirement of a communication power supply for high power density and high efficiency, synchronous rectification technology is widely used in DC-DC power converters. However, since a rectifier diode will generate a considerable conduction loss, a rectification circuit composed of transistors replaces a circuit composed of rectifier diodes. Compared with the circuit using rectifier diodes, the circuit using transistors for rectification has lower circuit loss and high efficiency, and meanwhile has higher requirement for reliability of transistor control. Therefore it is needed to eliminate interference due to a driver, misoperation and other abnormalities, these abnormalities will cause conductivity of upper and lower switching tubes in the same bridge arm of a synchronous rectifier circuit, resulting in the damage to the switching tube. A synchronous rectification control method commonly used in the related art generally includes: detecting the output current in a secondary winding of the transformer unit, and generating a first driving signal according to the output current, and then driving the on-and-off of a rectifier in the synchronous rectifier circuit by using the first driving signal.

A current sampling device is used to detect the output current (i.e., the current flowing through the parasitic diode of the synchronous rectifier) in the secondary winding of the transformer unit and turns on the synchronous rectifier when detecting that there is a current flowing through. However, a current detecting circuit has parasitic parameters, the signal of the output current is easily delayed, easily causing delays of turn-on and turn-off signals. Meanwhile, when the first driving signal is converted from the signal of the output current, there also exists a delay and there are also interference signals because it is easily affected by a power circuit. When amplitudes of these interference signals exceed the base drive voltage threshold of the synchronous rectifier, the synchronous rectifier will be mis-opened, and further the synchronous rectifier is directly conducted to cause the damage to the synchronous rectifier.

What is described below is a summary of the subject matter described in detail in this text. This summary is not intended to limit the protection scope of claims.

Embodiments of the present disclosure provide a synchronous rectifier driving method, a synchronous rectifier circuit and a switching power supply and can accurately control on-and-off of a synchronous rectifier.

An embodiment of the present disclosure provides a synchronous rectifier driving method, used for driving a rectifier in a synchronous rectifier circuit. The synchronous rectifier driving method includes: detecting an output current in a secondary winding of a transformer unit, and generating a first driving signal according to the output current; the method includes:

obtaining a protection signal according to a voltage signal of the secondary winding of the transformer unit in the synchronous rectifier circuit;

correcting the first driving signal by using the obtained protection signal to obtain a second driving signal; and

driving the rectifier in the synchronous rectifier circuit according to the second driving signal.

In an exemplary embodiment, said obtaining a protection signal according to a voltage signal of the secondary winding of the transformer unit includes:

detecting a first voltage and a second voltage at two ends of the secondary winding of the transformer unit and obtaining the protection signal according to a comparison result of the first voltage and the second voltage.

In an exemplary embodiment, the protection signal includes a first voltage signal inputA and a second voltage signal inputB,

Said obtaining the protection signal according to a comparison result of the first voltage and the second voltage includes: when the first voltage VA is greater than the second voltage VB, the first voltage signal inputA is a high-level signal and the second voltage signal inputB is a low-level signal; when the first voltage VA is less than the second voltage VB, the first voltage signal inputA is a low-level signal and the second voltage signal inputB is a high-level signal.

In an exemplary embodiment, said correcting the first driving signal by using the obtained protection signal to obtain a second driving signal includes:

carrying out an AND operation on the first driving signal and the protection signal, using a result of the AND operation as the second driving signal.

An embodiment of the present disclosure further provides a synchronous rectifier circuit, including: a transformer unit, a current sampling unit, a first signal processing unit, a driving unit and a synchronous rectifier unit, the current sampling unit is configured to detect an output current in a secondary winding of the transformer unit; the first signal processing unit is configured to generate a first driving signal according to the output current in the secondary winding of the transformer unit; and the synchronous rectifier circuit further includes a protection unit and a second signal processing unit.

The protection unit is configured to obtain a protection signal according to a voltage signal of the secondary winding of the transformer unit in the synchronous rectifier circuit.

The second signal processing unit is configured to correct the first driving signal by using the obtained protection signal to obtain a second driving signal.

The driving unit is configured to drive a rectifier in the synchronous rectifier circuit according to the second driving signal.

In an exemplary embodiment, the transformer unit includes one or more transformers and each transformer includes one or more secondary windings; the current sampling unit includes a first instrument transformer and a rectification circuit. A primary side of the first instrument transformer is connected in series to a first secondary winding which is one of secondary windings corresponding to any transformer; a secondary side of the first instrument transformer is connected to the rectification circuit; the rectification circuit generates a first voltage signal VR left and a second voltage signal VR right according to a current signal output by the first instrument transformer.

In an exemplary embodiment, the first signal processing unit includes a first comparison circuit, and the first driving signal includes a third voltage signal V left and a fourth voltage signal V right . A reference voltage V ref1 is set in the first comparison circuit and the first comparison circuit obtains the third voltage signal V left by comparing the first voltage signal VR left with the reference voltage V ref1 and obtains the fourth voltage signal V right by comparing the second voltage signal VR right with the reference voltage V ref1 , the third voltage signal V left and the fourth voltage signal V right are both square signals.

In an exemplary embodiment, the protection unit includes a voltage detecting circuit and a second comparison circuit, the protection signal includes a fifth voltage signal inputA and a sixth voltage signal inputB. Input ends of the voltage detecting circuit are respectively connected to two ends of a second secondary winding, and detected seventh voltage signal V A and eighth voltage signal V B are provided to the second comparison circuit, the second secondary winding is one of secondary windings corresponding to any transformer. The second comparison circuit compares the seventh voltage signal V A and the eighth voltage signal V B according to the detected seventh voltage signal V A and eighth voltage signal V B to obtain the fifth voltage signal inputA and the sixth voltage signal inputB.

In an exemplary embodiment, the protection signal includes the fifth voltage signal inputA and the sixth voltage signal inputB. The second comparison circuit is configured as that: when the seventh voltage signal V A is greater than the eighth voltage signal V B , the output fifth voltage signal inputA is a high-level signal and the output sixth voltage signal inputB is a low-level signal; when the seventh voltage signal V A is less than the eighth voltage signal V B , the output fifth voltage signal inputA is a low-level signal and the output sixth voltage signal inputB is a high-level signal.

In an exemplary embodiment, the second signal processing unit is configured to carry out an AND operation on the first driving signal and the protection signal, use a result of the AND operation as the second driving signal; the second driving signal includes a first driving signal outputA and a second driving signal outputB. An AND operation is carried out on the third voltage signal V left and the fifth voltage signal inputA to obtain the first driving signal outputA; an AND operation is carried out on the fourth voltage signal V right and the sixth voltage signal inputB to obtain the second driving signal outputB.

An embodiment of the present disclosure further provides a switching power supply, including any of the above mentioned synchronous rectifier circuits.

Compared with the related art, the solution provided in the embodiments of the present disclosure includes: obtaining a protection signal according to a voltage signal of a secondary winding of a transformer unit in the synchronous rectifier circuit, wherein a synchronous reversal occurs in the protection signal according to a level reversal of a primary winding of the transformer unit; correcting the first driving signal by using the obtained protection signal to obtain a second driving signal; and driving a rectifier in the synchronous rectifier circuit according to the second driving signal. In the related art, turning-on and turning-off of the synchronous rectifier are controlled only through the first driving signal. In the embodiments of the present disclosure, since the synchronous reversal can occur in the protection signal can synchronously according to the level reversal of the primary winding of the transformer unit, the second driving signal is obtained by correcting the first driving signal by using the protection signal, the high level of the first driving signal is eliminated in a delay region, thus eliminating the delay phenomenon of level reversal in the first driving signal, avoiding a misoperation of turning on the synchronous rectifier, thereby reducing damage to the synchronous rectifier, improving the performance of the synchronous rectifier circuit, and improving the performance of the switching power supply including the synchronous rectifier circuit.

Other aspects will become apparent upon reading and understanding the drawings and detailed description.

FIG. 1 is a schematic flow chart of a synchronous rectifier driving method provided in embodiment 1 of the present disclosure.

FIG. 2 is a block diagram of a synchronous rectifier circuit provided in embodiment 2 of the present disclosure.

FIG. 3A , FIG. 3B , FIG. 3C , FIG. 3D , FIG. 3E and FIG. 3F are respectively circuit structure diagrams of the synchronous rectifier circuit provided in application examples of the present disclosure.

FIG. 4A is a circuit structure diagram of a rectification circuit provided in an application example of the present disclosure.

FIG. 4B is a circuit structure diagram of a first comparison circuit provided in an application example of the present disclosure.

FIG. 4C is a circuit structure diagram of a voltage detecting circuit provided in an application example of the present disclosure.

FIG. 4D is a circuit structure diagram of a second comparison circuit provided in an application example of the present disclosure.

FIG. 4E is a circuit structure diagram of an interlocking circuit provided in an application example of the present disclosure.

FIG. 5 is a schematic diagram of the comparison of multiple signals in the synchronous rectifier circuit.

Embodiments of the present disclosure will be described below in further detail with reference to the accompanying drawings. It should be noted that, in the case of no conflict, embodiments in this application and various modes in the embodiments may be combined with each other.

Referring to FIG. 1 , an embodiment of the present disclosure provides a synchronous rectifier driving method, used for driving a rectifier in a synchronous rectifier circuit. The synchronous rectifier circuit includes a transformer unit, and the synchronous rectifier driving method includes: detecting an output current in a secondary winding of a transformer unit, and generating a first driving signal according to the output current; the method includes steps 100 , 200 , 300 .

In Step 100 , a protection signal is obtained according to a voltage signal of a secondary winding of the transformer unit; herein a synchronous reversal occurs in the protection signal according to a level reversal in a primary winding of the transformer unit.

Herein, obtaining a protection signal according to a voltage signal of the secondary winding of the transformer unit includes: detecting a first voltage and a second voltage at two ends of the secondary winding of the transformer unit and obtaining the protection signal according to a comparison result of the first voltage and the second voltage.

Herein, obtaining the protection signal according to the comparison result of the first voltage and the second voltage includes: the protection signal includes a voltage signal inputA and a voltage signal inputB; when the first voltage VA is greater than the second voltage VB, the voltage signal inputA is a high-level signal and the voltage signal inputB is a low-level signal; when the first voltage VA is less than the second voltage VB, the voltage signal inputA is a low-level signal and the voltage signal inputB is a high-level signal.

In Step 200 , the second driving signal is obtained according to the first driving signal and the protection signal (the first driving signal is corrected by using the obtained protection signal) includes: carrying out an AND operation on the first driving signal and the protection signal, using a result of the AND operation as the second driving signal.

In Step 300 , the rectifier in the synchronous rectifier circuit is driven according to the second driving signal.

Based on a concept same as or similar to that in the foregoing embodiment, an embodiment of the present disclosure further provides a synchronous rectifier circuit. FIG. 2 is a block diagram of the synchronous rectifier circuit provided in an embodiment of the present disclosure. As shown in FIG. 2 , the synchronous rectifier circuit provided in the embodiment of the present disclosure includes: a transformer unit 10 , a current sampling unit 20 , a first signal processing unit 30 , a protection unit 40 , a second signal processing unit 50 , a driving unit 60 , and a synchronous rectifier unit 70 .

The current sampling unit 20 is configured to detect an output current in a secondary winding of the transformer unit 10 .

The first signal processing unit is configured to generate a first driving signal according to the output current in the secondary winding of the transformer unit 10 .

The protection unit 40 is configured to obtain a protection signal according to a voltage signal of the secondary winding of the transformer unit in the synchronous rectifier circuit.

The second signal processing unit 50 is configured to correct the first driving signal by using the obtained protection signal to obtain a second driving signal.

The driving unit 60 is configured to drive a rectifier in the synchronous rectifier circuit according to the second driving signal.

Herein a synchronous reversal occurs in the protection signal according to the level reversal in a primary winding of the transformer unit 10 .

Herein the synchronous rectifier in the synchronous rectifier unit 70 is connected to the secondary winding of the transformer unit 10 .

In the embodiment of the present disclosure, the transformer unit 10 includes one or more transformers and each transformer includes one or more secondary windings; the current sampling unit 20 includes a first instrument transformer and a rectification circuit.

The primary side of the first instrument transformer is connected in series to a first secondary winding which is one of secondary windings corresponding to any transformer; the secondary side of the first instrument transformer is connected to the rectification circuit; the rectification circuit generates voltage signals V left and VR right according to a current signal output by the first instrument transformer.

In an embodiment of the present disclosure, the first signal processing unit 30 includes a first comparison circuit, and the first driving signal includes voltage signals V left and V right .

A reference voltage V ref1 is set in the first comparison circuit and the first comparison circuit obtains the voltage signal V left by comparing the voltage signal VR left with the reference voltage V ref1 and obtains the voltage signal V right through comparing the voltage signal VR right with the reference voltage V ref1 , herein the voltage signals V left and V right are both square signals.

In an embodiment of the present disclosure, the protection unit 40 includes a voltage detecting circuit and a second comparison circuit, the protection signal includes voltage signals inputA and inputB.

Input ends of the voltage detecting circuit are respectively connected to two ends of a second secondary winding, and detected voltage signals V A and V B are provided to the second comparison circuit, herein the second secondary winding is one of secondary windings corresponding to any transformer.

The second comparison circuit compares the voltage signals V A and V B according to the detected voltage signals V A and V B to obtain the voltage signals inputA and inputB. The second comparison circuit is configured as that: when the voltage signal V A (the first voltage VA in the foregoing method) is greater than the voltage signal V B (the second voltage VB in the foregoing method), the output voltage signal inputA is a high-level signal and the output voltage signal inputB is a low-level signal; when the voltage signal V A is less than the voltage signal V B , the output voltage signal inputA is a low-level signal and the output voltage signal inputB is a high-level signal.

In an embodiment of the present disclosure, the second signal processing unit is configured to carry out an AND operation on the first driving signal and the protection signal, use the result of the AND operation as the second driving signal; the second driving signal includes a driving signal outputA and a driving signal outputB.

An AND operation is carried out on the voltage signal V left and the voltage signal inputA to obtain the driving signal outputA; an AND operation is carried out on the voltage signal V right and the voltage signal inputB to obtain the driving signal outputB.

The following description is set forth with reference to application scenarios.

APPLICATION EXAMPLE 1

Referring to FIG. 3A , based on the synchronous rectifier circuit provided in the foregoing embodiment, this example provides a synchronous rectifier circuit. As shown in FIG. 3A , in the synchronous rectifier circuit, the transformer unit 10 includes a transformer T 1 ; the transformer T 1 includes a secondary winding, the synchronous rectifier unit 70 includes four rectifiers which respectively are rectifiers SR 1 , SR 2 , SR 3 and SR 4 , where SR 1 and SR 3 are on the same bridge arm and SR 2 and SR 4 are on the same bridge arm.

The current sampling unit 20 includes a first instrument transformer (the current transformer T 2 in this example) and a rectification circuit; a primary side of the current transformer T 2 is connected in series to a secondary winding of the transformer T 1 , and a secondary side of the current transformer T 2 is connected to the rectification circuit. The current transformer T 2 is connected in series with the secondary winding of the transformer T 1 and then connected to a source electrode of the full-bridge synchronous rectifier SR 1 ; a current detected by the primary side of the current transformer T 2 is an alternating current signal, and two ends of the secondary side of the current transformer T 2 are connected with the rectification circuit. The rectification circuit generates voltage signals VR left and VR right according to a current signal output by the first instrument transformer T 2 .

A reference voltage V ref1 is set in the first comparison circuit (the comparison circuit 1 in this example) and the first comparison circuit obtains the voltage signal V left by comparing the voltage signal VR left with the reference voltage V ref1 and obtains the voltage signal V right by comparing the voltage signal VR right with the reference voltage V ref1 . The voltage signals V left and V right are both square signals.

The protection unit 40 includes a voltage detecting circuit and a second comparison circuit (the comparison circuit 2 in this example), the protection signal includes voltage signals inputA and inputB. Input ends of the voltage detecting circuit are respectively connected to two ends of the second secondary winding. Herein the voltage detecting circuit respectively detects a voltage to earth of a source electrode point A of the synchronous rectifier SR 1 and a voltage to earth of a drain electrode point B of the synchronous rectifier SR 4 to obtain voltage signals V A and V B , the voltage detecting circuit provides the detected voltage signals V A and V B to the comparison circuit 2 , and the second comparison circuit compares the voltage signals V A and V B based on the detected voltage signals V A and V B to obtain voltage signals inputA and inputB (the protection signal).

Obtaining the protection signal according to the comparison result of the first voltage and the second voltage includes: the protection signal includes a voltage signal inputA and a voltage signal inputB; when the voltage signal V A is greater than the voltage signal V B , inputA is a high-level signal and inputB is a low-level signal; when the voltage signal V A is less than the voltage signal V B , inputA is a low-level signal and inputB is a high-level signal.

The second signal processing unit 50 (an interlocking circuit in this example) is configured to obtain the second driving signal (signals inputA and inputB) according to the first driving signal and the protection signal. A logic “AND” operation processing is performed on the V left and V right with the protection signals inputA and inputB respectively through the interlocking circuit to generate signals outputA and outputB.

The driving unit 60 (a driving circuit in this example) is configured to drive all the rectifiers in the synchronous rectifier unit 70 according to the second driving signal. The signal V left , after being transformed, finally corresponds to driving voltage signals V g (SR 1 , SR 4 ) between the base electrodes and the source electrodes of the synchronous rectifiers SR 1 and SR 4 , that is, the signal outputA is transformed to obtain V g (SR 1 , SR 4 ) which are used to drive the synchronous rectifiers SR 1 and SR 4 ; the signal V right , after being transformed, finally corresponds to driving voltage signals V g (SR 2 , SR 3 ) between the base electrodes and the source electrodes of the synchronous rectifiers SR 2 and SR 3 , that is, the signal outputB is transformed to obtain V g (SR 2 , SR 3 ), which are used to drive the synchronous rectifiers SR 2 and SR 3 .

APPLICATION EXAMPLE 2

Referring to FIG. 3B , based on the concept same as or similar to that of the synchronous rectifier circuit provided in the foregoing embodiment, this example provides a synchronous rectifier circuit. In connection with FIG. 3B , in the synchronous rectifier circuit, the transformer unit 10 includes a transformer T 1 ; each transformer includes two secondary windings IS 12 and IS 13 which are connected in parallel, and each secondary winding is respectively connected to a full-bridge synchronous rectifier circuit. The synchronous rectifier unit 70 includes eight synchronous rectifiers which respectively are SR 1 , SR 2 , SR 3 , SR 4 , SR 5 , SR 6 , SR 7 and SR 8 , where SR 1 and SR 3 are on the same bridge arm, SR 2 and SR 4 are on the same bridge arm, SR 5 and SR 6 are on the same bridge arm, and SR 7 and SR 8 are on the same bridge arm.

The current sampling unit 20 includes a first instrument transformer (the current transformer T 2 in this example) and a rectification circuit; a primary side of the current transformer T 2 is connected in series to a secondary winding IS 12 of the transformer T 1 , and a secondary side of the current transformer T 2 is connected to the rectification circuit. The current transformer T 2 is connected in series with the secondary winding IS 12 of the transformer T 1 and then connected to a source electrode of the full-bridge synchronous rectifier SR 1 , and two ends of the secondary side of the current transformer T 2 are connected with the rectification circuit. The rectification circuit generates voltage signals VR left and VR right according to a current signal output by the first instrument transformer T 2 .

A reference voltage V ref1 is set in the first comparison circuit (the comparison circuit 1 in this example) and the first comparison circuit obtains the voltage signal V left by comparing the voltage signal VR left with the reference voltage V ref1 and obtains the voltage signal V right by comparing the voltage signal VR right with the reference voltage V ref1 . The voltage signals V left and V right are both square signals.

The protection unit 40 includes a voltage detecting circuit and a second comparison circuit (the comparison circuit 2 in this example), the protection signal includes voltage signals inputA and inputB. Input ends of the voltage detecting circuit are respectively connected to two ends of the secondary winding IS 13 . The voltage detecting circuit respectively detects the voltage to earth of a source electrode point A of the synchronous rectifier SR 5 and the voltage to earth of a drain electrode point B of the synchronous rectifier SR 8 to obtain voltage signals V A and V B . The voltage detecting circuit provides the detected voltage signals V A and V B to the comparison circuit 2 , and the second comparison circuit compares the voltage signals V A and V B based on the detected voltage signals V A and V B to obtain a protection signal (voltage signal inputA and voltage signal inputB).

In this example, the signal V left , after circuit transformation is performed, finally corresponds to driving voltage signals V g (SR 1 , SR 4 , SR 5 , SR 8 ) between the base electrodes and the source electrodes of the synchronous rectifiers SR 1 , SR 4 , SR 5 , SR 8 ; the signal V right , after circuit transformation is performed, finally corresponds to driving voltage signals V g (SR 2 , SR 3 , SR 6 , SR 7 ) between the base electrodes and the source electrodes of the synchronous rectifiers SR 2 , SR 3 , SR 6 , SR 7 .

In this example, the current transformer and the secondary winding IS 12 are connected in series, and the voltage detecting circuit and the secondary winding IS 13 are connected in parallel. In addition, it also can be implemented by arranging the current transformer and the voltage detecting circuit in the same full-bridge synchronous rectifier circuit, that is, both the current transformer and the voltage detecting circuit are connected to the same secondary winding IS 12 , or both the current transformer and the voltage detecting circuit are connected to the same secondary winding IS 13 .

APPLICATION EXAMPLE 3

Referring to FIG. 3C , based on the concept same as or similar to that of the synchronous rectifier circuit provided in the foregoing embodiment, this example provides a synchronous rectifier circuit. In connection with FIG. 3C , in the synchronous rectifier circuit, the transformer unit 10 includes transformers T 1 and T 2 and the primary windings of the transformers T 1 and T 2 are connected in series; each transformer includes one secondary winding, the secondary winding corresponding to the transformer T 1 is secondary winding IS 12 , the secondary winding corresponding to the transformer T 2 is secondary winding IS 13 , and each secondary winding is respectively connected to a full-bridge synchronous rectifier circuit. The synchronous rectifier unit 70 includes eight synchronous rectifiers which respectively are SR 1 , SR 2 , SR 3 , SR 4 , SR 5 , SR 6 , SR 7 and SR 8 , where SR 1 and SR 3 are on the same bridge arm, SR 2 and SR 4 are on the same bridge arm, and a synchronous rectifier unit 70 consisting of SR 1 , SR 2 , SR 3 , SR 4 is connected to the secondary winding IS 12 ; SR 5 and SR 6 are on the same bridge arm, SR 7 and SR 8 are on the same bridge arm, and a synchronous rectifier unit 70 consisting of SR 5 , SR 6 , SR 7 , SR 8 is connected to the secondary winding IS 13 .

The current sampling unit 20 includes a first instrument transformer (the current transformer T 2 in this example) and a rectification circuit; a primary side of the current transformer T 2 is connected in series to a secondary winding IS 12 of the transformer T 1 , and a secondary side of the current transformer T 2 is connected to the rectification circuit. The current transformer T 2 is connected in series with the secondary winding IS 12 of the transformer T 1 and then connected to a source electrode of the full-bridge synchronous rectifier SR 1 , and two ends of the secondary side of the current transformer T 2 are connected with the rectification circuit. The rectification circuit generates voltage signals VR left and VR right according to a current signal output by the first instrument transformer T 2 .

A reference voltage V ref1 is set in the first comparison circuit (the comparison circuit 1 in this example) and the first comparison circuit obtains the voltage signal V left by comparing the voltage signal VR left with the reference voltage V ref1 and obtains the voltage signal V right by comparing the voltage signal VR right with the reference voltage V ref1 . The voltage signals V left and V right are both square signals.

The protection unit 40 includes a voltage detecting circuit and a second comparison circuit (the comparison circuit 2 in this example), the protection signal includes voltage signals inputA and inputB. Input ends of the voltage detecting circuit are respectively connected to two ends of the secondary winding IS 13 . The voltage detecting circuit respectively detects the voltage to earth of a source electrode point A of the synchronous rectifier SR 5 and the voltage to earth of a drain electrode point B of the synchronous rectifier SR 8 to obtain voltage signals V A and V B . The voltage detecting circuit provides the detected voltage signals V A and V B to the comparison circuit 2 , and the second comparison circuit compares the voltage signals V A and V B based on the detected voltage signals V A and V B to obtain voltage signals inputA and inputB (the protection signal).

In this example, the signal V left , after circuit transformation is performed, finally corresponds to driving voltage signals V g (SR 1 , SR 4 , SR 5 , SR 8 ) between the base electrodes and the source electrodes of the synchronous rectifiers SR 1 , SR 4 , SR 5 , SR 8 ; the signal V right , after circuit transformation is performed, finally corresponds to driving voltage signals V g (SR 2 , SR 3 , SR 6 , SR 7 ) between the base electrodes and the source electrodes of the synchronous rectifiers SR 2 , SR 3 , SR 6 , SR 7 .

By using two transformers T 1 and T 2 connected in series, in the case of achieving the same power output, with respect to the structure of the synchronous rectifier circuit in FIG. 3A , in this example, the power undertaken by a single transformer becomes smaller, so the selection of the transformer type is more flexible. Meanwhile, with respect to the synchronous rectifier unit 70 shown in FIG. 1 , in this example, synchronous rectification is implemented through eight synchronous rectifiers, the power of a single synchronous rectifier is reduced, the efficiency is higher, and the selection of the transformer type is more flexible. Based on the above factors, the efficiency of the synchronous rectifier circuit becomes high.

In this example, the current transformer and the secondary winding IS 12 are connected in series, and the voltage detecting circuit and the secondary winding IS 13 are connected in parallel. In addition, it also can be implemented by arranging the current transformer and the voltage detecting circuit in the same full-bridge synchronous rectifier circuit, that is, both the current transformer and the voltage detecting circuit are connected to the same secondary winding IS 12 , or both the current transformer and the voltage detecting circuit are connected to the same secondary winding IS 13 .

APPLICATION EXAMPLE 4

Referring to FIG. 3D , based on the concept same as or similar to the concept of the synchronous rectifier circuit provided in the foregoing embodiment, this example provides a synchronous rectifier circuit. The difference between the synchronous rectifier circuit provided in this example and the synchronous rectifier circuit shown in FIG. 3A lies in that the synchronous rectifier circuit provided in this example is a full-wave double-voltage synchronous rectifier circuit.

As shown in FIG. 3D , in the synchronous rectifier circuit, the transformer unit 10 includes a transformer T 1 ; the transformer T 1 includes a secondary winding, the synchronous rectifier unit 70 includes two rectifiers SR 1 and SR 2 and two capacitors C 1 and C 2 .

The current sampling unit 20 includes a first instrument transformer (the current transformer T 2 in this example) and a rectification circuit; a primary side of the current transformer T 2 is connected in series to a secondary winding of the transformer T 1 , and a secondary side of the current transformer T 2 is connected to the rectification circuit. The current transformer T 2 is connected in series with the secondary winding of the transformer T 1 and then connected to a source electrode of the full-bridge synchronous rectifier SR 1 ; a current detected by the primary side of the current transformer T 2 is an alternating current signal, and two ends of the secondary side of the current transformer T 2 are connected with the rectification circuit. The rectification circuit generates voltage signals VR left and VR right according to a current signal output by the first instrument transformer T 2 .

The protection unit 40 includes a voltage detecting circuit and a second comparison circuit (the comparison circuit 2 in this example), the protection signal includes voltage signals inputA and inputB. Input ends of the voltage detecting circuit are respectively connected to two ends of the second secondary winding. The voltage detecting circuit respectively detects the voltage to earth of a source electrode A of the synchronous rectifier SR 1 and the voltages of two ends of the capacitor C 2 to obtain voltage signals V A and V B , the voltage detecting circuit provides the detected voltage signals V A and V B to the comparison circuit 2 , and the second comparison circuit compares the voltage signals V A and V B based on the detected voltage signals V A and V B to obtain voltage signals inputA and inputB (the protection signal).

The driving unit 60 (the driving circuit in this example) is configured to drive all the rectifiers in the synchronous rectifier unit 70 according to the second driving signal. The signal V left , after being transformed, finally corresponds to a driving voltage signal V g (SR 1 ) between the base electrode and the source electrode of the synchronous rectifier SR 1 , that is, the signal outputA is transformed to obtain V g (SR 1 ) which is used to drive the synchronous rectifier SR 1 . The signal V right , after being transformed, finally corresponds to driving voltage signals V g (SR 2 , SR 3 ) between the base electrodes and the source electrodes of the synchronous rectifiers SR 2 and SR 3 , that is, the signal outputB is transformed to obtain V g (SR 2 ) which is used to drive the synchronous rectifier SR 2 .

APPLICATION EXAMPLE 5

Referring to FIG. 3E , based on the concept same as or similar to the concept of the synchronous rectifier circuit provided in the foregoing embodiment, this example provides a synchronous rectifier circuit. The difference between the synchronous rectifier circuit provided in this example and the synchronous rectifier circuit shown in FIG. 3D lies in that, in the synchronous rectifier circuit provided in this example, the secondary side of a main transformer T 1 is connected with two upper windings which are connected in parallel, and each secondary winding is respectively connected with a full-wave double-voltage synchronous rectifier circuit.

As shown in FIG. 3E , the current sampling device, i.e., the current transformer T 2 are connected to the first full-wave double-voltage synchronous rectifier circuit, and the voltage detecting circuit detects the voltage of two ends of the secondary winding of the second full-wave double-voltage synchronous rectifier circuit.

In this example, the signal Vleft, after circuit transformation is performed, finally corresponds to driving voltage signals V g (SR 1 ,SR 3 ) between the base electrodes and the source electrodes of the synchronous rectifiers SR 1 and SR 3 ; the signal V right , after circuit transformation is performed, finally corresponds to driving voltage signals V g (SR 2 , SR 4 ) between the base electrodes and the source electrodes of the synchronous rectifiers SR 2 and SR 4 .

In this example, it also can be implemented by arranging the current transformer and the voltage detecting circuit in the same full-wave double-voltage synchronous rectifier circuit.

In this example, the secondary side of the main transformer T 1 may also be connected with more than two secondary windings which are all connected in parallel. Each secondary winding is connected with a full-wave double-voltage synchronous rectifier circuit, the current sampling and voltage detection may be in the same full-wave double-voltage synchronous rectifier circuit and may also be located in two full-wave double-voltage synchronous rectifier circuit separately.

APPLICATION EXAMPLE 6

Referring to FIG. 3F , based on the concept same as or similar to the concept of the synchronous rectifier circuit provided in the foregoing embodiment, this example provides a synchronous rectifier circuit. The difference between the synchronous rectifier circuit provided in this example and the synchronous rectifier circuit shown in FIG. 3D lies in that the synchronous rectifier circuit provided in this example has two main transformers T 1 and T 3 , the secondary side of each of the two main transformers is connected with a full-wave double-voltage synchronous rectifier circuit and the primary windings of the two main transformers are connected in series.

As shown in FIG. 3F , the current sampling device, i.e., the current transformer T 2 , is connected to the first full-wave double-voltage synchronous rectifier circuit, and the voltage detecting circuit detects the voltages to earth of two ends of the secondary winding of the second full-wave double-voltage synchronous rectifier circuit.

In this example, the signal V left , after circuit transformation is performed, finally corresponds to driving voltage signals V g (SR 1 ,SR 3 ) between the base electrodes and the source electrodes of the synchronous rectifiers SR 1 and SR 3 . The signal V right , after circuit transformation is performed, finally corresponds to driving voltage signals V g (SR 2 , SR 4 ) between the base electrodes and the source electrodes of the synchronous rectifiers SR 2 and SR 4 .

In this example, it also can be implemented by arranging the current transformer and the voltage detecting circuit in the same full-bridge rectification circuit.

In this example, the current sampling device in the current sampling unit 20 is a current transformer, and the current signal of the secondary winding may also be detected in other ways. For example, by connecting a resistor in series with the secondary winding, the current signal of secondary winding can be detected.

In this example, the number of transformers in the transformer unit 10 may also be two or more. The primary windings of these main transformers are connected in series. The secondary winding of each main transformer is respectively connected to a full-wave double-voltage synchronous rectifier circuit. The current sampling unit 20 and the voltage detecting circuit can be arranged in the same full-bridge synchronous rectifier circuit and may also be arranged in two different full-bridge synchronous rectifier circuits separately.

APPLICATION EXAMPLE 7

Reference is made to FIG. 4A which is a circuit structure diagram of a rectification circuit provided in this example. As shown in FIG. 4A , the secondary IS 11 terminal of the current transformer T 2 is simultaneously connected with an anode of a rectifier diode D 1 and a cathode of a rectifier diode D 4 , the secondary IS 12 terminal of the current transformer T 2 is simultaneously connected to the cathode of the rectifier diode D 2 and the anode of the rectifier diode D 3 , a sensing resistor R 1 is connected between the cathode of the diode D 1 and the anode of the diode D 2 , a sensing resistor R 2 is connected between the cathode of the diode D 3 and the anode of the diode D 4 , the anodes of the diodes D 2 and D 4 are simultaneously connected to the ground signal, the signal VR right is generated between the cathode of the diode D 1 and the ground, and the signal VR left is generated between the cathode of the diode D 3 and the ground.

APPLICATION EXAMPLE 8

Reference is made to FIG. 4B which is a circuit structure diagram of a first comparison circuit provided in this example. As shown in FIG. 4B , the signal VR left is connected to the input “+” terminal of the comparison 1, and the signal VR right is connected to the input input “+” terminal of the comparison 2; the signal V ref1 is connected to the “−” terminals of the comparison 1 and the comparison 2 at the same time; the output signal of the comparison 1 is the signal V left and the output signal of the comparison 2 is the signal V right .

APPLICATION EXAMPLE 9

Reference is made to FIG. 4C which is a circuit structure diagram of a voltage detecting circuit provided in this example. As shown in FIG. 4C , the sensing resistors R 3 and R 4 are connected in series and then are connected between the point A and the ground signal; the sensing resistors R 5 and R 6 are connected in series and then are connected between the point B and the ground signal; the signal V A is generated at the connection point of the sensing resistors R 3 and R 4 and the signal V B is generated at the connection point of the sensing resistors R 5 and R 6 .

APPLICATION EXAMPLE 10

Reference is made to FIG. 4D which is a circuit structure diagram of a second comparison circuit provided in this example. As shown in FIG. 4D , the signal V A is connected to the input “−” terminal of the comparison 1 and the input “+” terminal of the comparison 2 at the same time, and the signal V B is connected to the input “+” terminal of the comparison 1 and the input “−” terminal of the comparison 2 at the same time, herein the output terminal signal of the comparison 1 is inputB and the output terminal signal of the comparison is inputA.

APPLICATION EXAMPLE 11

Reference is made to FIG. 4E which is a circuit structure diagram of an interlocking circuit provided in this example. As shown in FIG. 4E , the interlocking circuit includes two AND gates, the signal inputA and the signal V right are respectively connected to two input ends of the AND gate 1 , the signal inputB and signal V left are respectively connected to two input ends of AND gate 2 , the output signal of the AND gate 1 is outputA, and the output signal of the AND gate 2 is outputB.

With reference to the synchronous rectifier circuit shown in FIG. 3A , the working process of the circuit is analyzed hereinafter by taking one sinusoidal current cycle of a secondary current of the main transformer T 1 as an example. Reference is made to FIG. 5 which is a schematic diagram of the comparison of multiple signals in the synchronous rectifier circuit. As shown in FIG. 5 , when the secondary current I of the main transformer flows from a secondary dotted terminal and the current I increases from zero in a positive half cycle, if the output voltage VR left of the rectification circuit is lower than the reference voltage V ref1 , the signal V left is a low-level signal, the synchronous rectifiers SR 1 and SR 4 have no driving voltage, and the current I flows through the internal parasitic diodes of SR 1 and SR 4 . When the current I increases to a certain value, if the output voltage VR left of the rectification circuit is higher than the reference voltage V ref1 , and the signal V left is a high-level signal, and at this moment, the high-level signal drives the synchronous rectifiers SR 1 and SR 4 through the driving circuit to be turned on. When the current signal I is gradually reduced to zero, if the output voltage VR left of the rectification circuit is lower than the reference voltage V ref1 , the signal V left is a low-level signal and the synchronous rectifiers SR 1 and SR 4 are turned off.

When the current I of the main transformer is changed from the positive half cycle to a negative half cycle, if the output voltage VR right of the rectification circuit is lower than the reference voltage V ref1 , the signal V right is a low-level signal, the synchronous rectifiers SR 2 and SR 3 have no driving voltage, and the current I flows through the internal parasitic diodes of SR 2 and SR 3 . When the current I increases to a certain value, if the output voltage VR right of the rectification circuit is higher than the reference voltage V ref1 , and the signal V right becomes a high-level signal, and at this moment, the high-level signal drives the synchronous rectifiers SR 2 and SR 3 through the driving circuit to be turned on. When the current signal I is gradually reduced to zero, if the output voltage VR right of the rectification circuit is lower than the reference voltage V ref1 , the signal V right is a low-level signal and the synchronous rectifiers SR 2 and SR 3 are turned off.

However, due to the delay phenomenon in the signal processing circuit 1 , the output signals V left and V right of the comparison 1 and the comparison 2 also have a delay when the primary current of the current transformer has dropped to zero, as shown by dotted lines in the signals V left and V right in FIG. 5 . If the delay signals in V left and V right are left unprocessed, the synchronous rectifiers SR 1 and SR 3 , or SR 2 and SR 4 , on the same bridge arm will be turned on at the same time to cause a direct-conduction phenomenon, which can cause damage to the synchronous rectifiers.

In an embodiment of the present disclosure, the voltages to earth at point A and point B, V A and V B , in the figure are detected by using the voltage detecting circuit. When the secondary current I of the transformer is positive (the current flows out from the secondary dotted terminal of the transformer), the voltage to earth at point A, V A , is higher than the voltage to earth at point B, V B , the output inputB of the comparison 3 is low-level and the output inputA of the comparison 4 is high-level. When the current is changed from the positive half to a negative half cycle, the voltage to earth at point A, V A , is lower than the voltage to earth at point B, V B , and when the output inputB of the comparison 3 changes from a low level to a high level, the output inputA of comparison 4 changes from a high level to a low level. Due to no delay in the secondary current of the transformer, signals inputA and inputB will flip accurately following zero-crossing of the primary current of the transformer (the waveforms are shown in FIG. 5 ).

In the interlocking circuit, an “AND” operation is carried out on inputA and inputB with V left and V right respectively. Since inputA and inputB are accurate without delay, although V left and V right are at a high level at the same time due to delay of V left and V right , as shown by the shaded areas in FIG. 5 , after the “AND” operation is carried out on inputA and inputB with V left and V right respectively, the output signals outputA and outputB will not be at a high level at the same time as what happens in the related art. In this case, the signal outputA is used to drive the synchronous rectifiers SR 1 and SR 4 to be conducted and the signal outputB is used to drive synchronous rectifier SR 2 and SR 3 to be conducted, and therefore two switching tubes on the same bridge arm would not be conducted at the same time, thus avoiding the damage to the synchronous rectifiers.

Based on a concept same as or similar to the concepts in the foregoing embodiments, an embodiment of the present disclosure further provides a switching power supply, including any of the synchronous rectifier circuits provided by the foregoing embodiments.

In the embodiments of the present disclosure, since the synchronous reversal can occur in the protection signal according to the level reversal of the primary winding of the transformer unit, the second driving signal is obtained by correcting the first driving signal by using the protection signal, the high level of the first driving signal is eliminated in a delay region, thus eliminating the delay phenomenon of level reversal in the first driving signal, avoiding a misoperation of turning on the synchronous rectifier, thereby reducing damage to the synchronous rectifier, improving the performance of the synchronous rectifier circuit, and improving the performance of the switching power supply including the synchronous rectifier circuit.