Converter and method for controlling thereof

The present disclosure relates to a method for controlling a converter. More particularly, the present disclosure relates to a method for controlling a converter to achieve a zero voltage switching.

A DC voltage is commonly required for operating an electric device. Therefore, an AC-DC power supply or a DC-DC power supply is needed for outputting a rectified DC voltage. A converter is commonly employed in such AC-DC (or DC-DC) power supply to convert a voltage. Many kinds of circuit topologies such as a forward topology, a flyback topology, a CUK topology, a full bridge topology, a half bridge topology and a push pull topology are used in the converter. Conventionally, a converter may include a primary side rectifier having a primary side switch and a secondary side rectifier having a secondary side switch for modulating an outputted voltage.

In switch mode power supplies utilizing the aforementioned converters, a zero voltage switching (ZVS) is desired for the primary side switch; because of a relatively high voltage on the primary side switch that inducing a turn-on loss.

There exists a parasitic tank circuit oscillation in when the secondary side rectifier is turned off completing the discharging of the transformer energy, and before the turn on of the primary side switch. However, the parasitic tank circuit oscillation while provides a voltage valley, it does not produce a ZVS for the primary side switch to take advantage of.

According to one aspect of the present disclosure, a method for controlling a converter is provided. The converter includes a first switch and a second switch. The method includes: turning on then turning off the first switch for storing an energy in the converter; turning on then turning off the second switch for transferring the stored energy in the converter; turning on the second switch again and then turning off the second switch thereby injecting the energy into the converter for generating oscillations so as to achieve a near zero voltage when the first switch being turned on again in a next operation cycle.

According to another aspect of the present disclosure, a method for controlling a converter is provided. The converter includes a primary side circuit and a secondary side circuit. The method includes: providing a first switch in the primary side circuit; providing a second switch in the secondary side circuit; turning on then turning off the first switch for storing an energy in the converter; turning on then turning off the second switch for transferring the stored energy in the converter; turning on the second switch again and then turning off the second switch for injecting energy into the converter for generating oscillations so as to achieve a near zero voltage synchronously with the first switch being turned on again in a next operation cycle.

According to still another aspect of the present disclosure, a converter is provided. The converter includes a first switch and a second switch. The first switch is turned on then turned off for storing an energy in the converter, the second switch is turned on then turned off for transferring the stored energy in the converter; the second switch is turned on again thereby injecting the energy into the converter, and the second switch is turned off to increase levels of oscillations.

According to further another aspect of the present disclosure, a converter is provided. The converter includes a primary side circuit and a secondary side circuit. The primary side circuit includes a first switch. The secondary side circuit includes a second switch. The first switch is turned on then turned off for storing an energy in the converter, the second switch is turned on then turned off for transferring the stored energy in the converter, the second switch is turned on again for injecting the energy into the converter, synchronously with the converter oscillations and the second switch is then turned off to increase levels of oscillations.

FIG. 1 is a flow chart showing a method for controlling a converter according to one embodiment of the present disclosure.

FIG. 2 is a flow chart showing a method for controlling a converter according to another embodiment of the present disclosure.

FIG. 3 shows a circuit topology of a converter that utilizing the method of FIG. 1 .

FIG. 4 shows an operation mode of the converter of FIG. 3 without a zero voltage switching.

FIG. 5 shows an operation mode of the converter of FIG. 3 with a zero voltage switching.

FIG. 6 shows a circuit topology of a converter that utilizing the method of FIG. 2 .

FIG. 7 shows the converter of FIG. 6 operated under a heavy load without a zero voltage switching.

FIG. 8 shows the converter of FIG. 6 operated under a light load without a zero voltage switching.

FIG. 9 shows the converter of FIG. 6 operated under a heavy load with a zero voltage switching.

FIG. 10 shows the converter of FIG. 6 operated under a light load with a zero voltage switching.

FIG. 11 is a waveform diagram showing a zero voltage switching operation of the converter of FIG. 6 .

FIG. 1 is a flow chart showing a method for controlling a converter according to one embodiment of the present disclosure. In FIG. 1 , the method for controlling the converter includes a step S 101 , a step S 102 and a step S 103 . The converter includes a first switch and a second switch. In the step S 101 , the first switch is turned on then turned off for storing an energy in the converter. In the step S 102 , the second switch is turned on then turned off for transferring the stored energy in the converter. In the step S 103 , the second switch is turned on again and then the second switch is turned off thereby injecting the energy into the converter for generating oscillations so as to achieve a near zero voltage when the first switch being turned on again in a next operation cycle.

FIG. 2 is a flow chart showing a method for controlling a converter according to another embodiment of the present disclosure. In FIG. 2 , the method for controlling the converter includes a step S 201 , a step S 202 , a step S 203 , a step S 204 and a step S 205 . The converter includes a primary side circuit and a secondary side circuit. In the step S 201 , a first switch is provided in the primary side circuit. In the step S 202 , a second switch is provided in the secondary side circuit. In the step S 203 , the first switch is turned then turned off for storing an energy in the converter. In the step S 204 , the second switch is turned then turned off for transferring the stored energy in the converter. In the step S 205 , the second switch is turned on again and then the second switch is turned off for injecting the energy into the converter for generating oscillations so as to achieve a near zero voltage synchronously with the first switch being turned on again in a next operation cycle.

It should be known that the method of the present disclosure can be applied on a converter having a single circuit with two switches or a converter having a dual-sided circuit with two switches.

FIG. 3 shows a circuit topology of a converter that utilizing the method of FIG. 1 . In FIG. 3 , the converter includes a single circuit with a primary side 200 and a secondary side 300 . The primary side 200 includes a first switch 210 , an auxiliary winding 220 , and a controller 230 . The first switch 210 has a first voltage V 1 thereon. The auxiliary winding 220 has a first terminal and a second terminal, wherein the first terminal of the auxiliary winding 220 may be coupled to a conventional auxiliary power input circuit, and the second terminal of the auxiliary winding 220 may be coupled to a ground GND, but the disclosure is not limited thereto.

The controller 230 is coupled to the first switch 210 and capable of retrieving the first voltage V 1 . Specifically, the controller 230 has an input terminal coupled to a first terminal of the first switch 210 , a first output terminal coupled to a control terminal of the first switch 210 , a second output terminal, and a ground terminal coupled to a second terminal of the first switch 210 and the ground GND.

The primary side 200 may further include a power source 240 , a first winding 250 , and an auxiliary power input 260 . The power source 240 may be a conventional AC source input including an AC power, a full bridge rectifier, etc., wherein a first terminal of the power source 240 may be coupled to a first terminal of the first winding 250 , and a second terminal of the power source 240 may be coupled to the ground GND. A second terminal of the first winding 250 is coupled to the first terminal of the first switch 210 and the input terminal of the controller 230 . A first terminal of the auxiliary power input 260 is coupled to a first terminal of the auxiliary winding 220 , and a second terminal of the auxiliary power input 260 is coupled to the ground GND.

The secondary side 300 is coupled to the primary side 200 and includes a second switch 310 and a pulse transformer 320 coupled to the second switch 310 . Specifically, the second switch 310 may be an SRMOS (which operates as a body diode 312 when being turned off) and has a first terminal, a second terminal, and a control terminal. The pulse transformer 320 has a first input terminal coupled to the first terminal of the second switch 310 , a second input terminal coupled to the second output terminal of the controller 230 , an output terminal coupled to the control terminal of the second switch 310 , and a ground terminal coupled to the ground GND. In one embodiment, the pulse transformer 320 turns off the second switch 310 in response to a command CMD from the controller 230 .

The secondary side 300 may further include a second winding 330 and an output capacitor 340 . The second winding 330 has a first terminal and a second terminal, wherein the second terminal of the second winding 330 is coupled to the second terminal of the second switch 310 . The output capacitor 340 has a first terminal and a second terminal, wherein the first terminal of the output capacitor 340 is coupled to the first terminal of the second winding 330 , and the second terminal of the output capacitor 340 is coupled to the first terminal of the second switch 310 .

FIG. 4 shows an operation mode of the converter of FIG. 3 without a zero voltage switching. FIG. 5 shows an operation mode of the converter of FIG. 3 with a zero voltage switching. In FIG. 4 , while in operating the converter in FIG. 3 , firstly, the first switch 210 is turned on then turned off (duration from a timing point t 0 to a timing point t 1 ) for storing energy and the controller 230 retrieves the first voltage V 1 as a specific voltage. And then, the second switch 310 is turned on then turned off (duration from the timing point t 1 to a timing point t 2 ) for transferring the stored energy in the converter, an oscillation waveform of the specific voltage is generated after the second switch 310 is turned off in a cycle 1 . In FIG. 4 , when the first switch 210 is turned on again in a next cycle (cycle 2 ), a relatively high voltage exists, thereby inducing a turn-on loss (or switch loss), therefore the zero voltage switching is not achieved. In FIG. 5 , an extra energy is injected into the converter by re-opening the second switch 310 (i.e. at a timing point t 3 , after closing the second switch 310 in the cycle 1 ), synchronously with the converter oscillations, and then the second switch 310 is turned off (i.e. before re-opening the first switch 310 in the cycle 2 ) to increase levels of oscillation (or from another view, to produce new oscillations in addition to the original converter oscillations). The increased level of the oscillations is generated due to extra oscillations generated by injecting an extra energy into the converter. When the first switch 210 is turned on again during the increased levels of the oscillations, a relatively low voltage exists thereby reducing energy consumption so that a turn-on loss (a switch loss) of the first switch S 1 can be reduced. The time that the first switch 310 re-opened in the cycle 2 is determined by detecting a lowest voltage value when the extra oscillations started.

FIG. 6 shows a circuit topology of a converter that utilizing the method of FIG. 2 .

In FIG. 6 , a converter includes a primary side circuit and a secondary side circuit. The primary side circuit includes a first controller 101 and a first switch S 1 controlled by the first controller 101 . The secondary side circuit includes a second controller 102 and a second switch S 2 controlled by the second controller 102 .

The second controller 102 controls the second switch S 2 to be turned on or turned off to feedback a message to the primary side circuit; and the first controller 101 controls the first switch S 1 to be turned on or turned off to transfer energy to the secondary side circuit if the first controller 101 receives the message. In one example, the first switch S 1 or the second switch S 2 may be a MOSFET, and when the first switch S 1 is turned on, the second switch S 2 should be turned off to prevent the damage of the MOSFET.

The primary side circuit includes a first winding 201 and an auxiliary winding 203 . The first winding 201 is coupled with the first switch S 1 and the first controller 101 . The auxiliary winding 203 is coupled with the first controller 101 .

The secondary side circuit includes a second winding 202 . The second winding 202 is coupled with the second switch S 2 .

The first winding 201 of the primary side circuit is coupled with the second winding 202 of the secondary side circuit to transfer energy from the primary side circuit to the secondary side circuit.

The message is transferred from the primary side circuit to the secondary side circuit through the coupling between the second winding 202 and the auxiliary winding 203 .

In the converter of FIG. 6 , the message is exchanged between the first controller 101 and the second controller 102 , thereby alternately dominating a regulation of an output voltage between the primary side circuit and the secondary side circuit in accordance with the message. Furthermore, the primary side circuit dominates the regulation of the output voltage in an initial state, and the secondary side circuit dominates the regulation of the output voltage in a steady state. Initially, when a pre-determined secondary side circuit modulation voltage is greater than a pre-determined primary side circuit modulation voltage; the first controller 101 and the second controller 102 are not in operation, and the primary side circuit is activated through a charging procedure (i.e., in FIG. 6 , when the input voltage VIN is received in the primary side circuit, the capacitor C 1 is charged through the resistance R 1 to provide the required electric power to activate the primary side circuit). Then, the output voltage Vo is increased to the pre-determined primary side circuit modulation voltage. Meanwhile, the primary side circuit dominates the modulation of the output voltage Vo, and the secondary side circuit is not in operation. When the output voltage Vo is greater than a threshold voltage level, the secondary side circuit starts to operate and dominate the modulation of the output voltage Vo. At this moment, the primary side circuit is passive, and the secondary circuit is active. The secondary side circuit turns on then turns off the second switch S 2 to transmit the message to the primary side circuit, and the primary side circuit turns on then turns off the first switch S 1 to transmit energy to the secondary side circuit after receiving the message. And then, the output voltage Vo can be increased to the pre-determined secondary side circuit modulation voltage after receiving the energy.

More specifically, in the converter of FIG. 6 , the energy is transmitted from the primary side circuit to the secondary side circuit through a coupling of the first winding 201 and the second winding 202 . The message is fed back to the primary side circuit through the coupling between the second winding 202 and the auxiliary winding 203 . The first switch S 1 is coupled to a control terminal gate of the first controller 101 , and the second switch S 2 is coupled to a control terminal gate of the second controller 102 . In FIG. 6 , the second controller 102 can be a synchronous rectifier (SR) controller.

In the flowing FIG. 7 , FIG. 8 , FIG. 9 and FIG. 10 , the symbol Tonp indicates that the period that the first switch S 1 is turned on; the symbol Tons indicates that the period that the second switch S 2 is turned on; the symbol Toff indicates that both of the first switch S 1 and the second switch S 2 are turned off.

FIG. 7 shows the converter of FIG. 6 operated under a heavy load without a zero voltage switching. FIG. 8 shows the converter of FIG. 6 operated under a light load without a zero voltage switching. The operation procedure of the converter of FIG. 6 has been described in the aforementioned paragraphs. The situations that the converter operated with and without a zero voltage switching will be then described.

FIG. 7 and FIG. 8 show the converter of FIG. 6 operated under a heavy load and a light load respectively. In FIG. 7 and FIG. 8 , in the situation that without a zero voltage switching, the first switch S 1 is turned on then turned off for storing an energy in the converter, and then the second switch S 2 is turned then turned off for transferring the stored energy in the converter. At the time, it can be observed that the oscillations of the converter are generated. In FIG. 7 and FIG. 8 , the oscillation frequency and the oscillation amplitude are different under a heavy load and a light load respectively. When in the next cycle that the first switch S 1 turned on again, a relatively high voltage exists, thereby inducing a turn-on loss (or switch loss), therefore the zero voltage switching is not achieved.

FIG. 9 shows the converter of FIG. 6 operated under a heavy load with a zero voltage switching. FIG. 10 shows the converter of FIG. 6 operated under a light load with a zero voltage switching. For reducing the turn-on loss in FIG. 7 and FIG. 8 , an extra procedure that achieving the zero voltage switching (ZVS) is used. In FIG. 9 and FIG. 10 , when the second switch S 2 is turned off, the second switch S 2 is turned on again for injecting energy into the converter, synchronously with the converter oscillations and then the second switch S 2 is turned off to increase levels of oscillations. Therefore, in the next cycle, when the first switch S 1 is turned on again during the increased levels of the oscillations, a relatively low voltage exists thereby reducing energy consumption so that a turn-on loss (a switch loss) of the first switch S 1 can be reduced. Accordingly, the ZVS allows the first switch S 1 to turn on using minimal energy, while a non ZVS of the first switch S 1 turned on is energy dissipative according to the voltage levels across the first switch S 1 . Furthermore, a capacitor Coss is disposed at a drain and a source of the first switch S 1 , thereby absorbing an energy by the capacitor when the first switch S 1 is turned off for recovering at turn on. In detail, the energy is injected into the converter in the form of an inductor current, and then turning off the second switch S 2 . With the second switch S 2 turned off, the continuous current from the inductor will now discharge the capacitance Coss across the first switch S 1 in the primary side circuit, and induce an extra oscillation which is used as near zero voltage switching of the first switch S 1 in the primary side circuit.

FIG. 11 is a waveform diagram showing a zero voltage switching operation of the converter of FIG. 6 . It is clearly shown that by introducing the method mentioned above, a voltage value of the primary side VDS(=VIN) is achieved to zero at a valley. While Q total-loss =Frequency×Coss×VIN (VDS), therefore the Q total-loss =Frequency×Coss×0 V=0. Therefore, energy consumption can be reduced.

Although the present disclosure has been described in considerable detail with reference to certain embodiments thereof, other embodiments are possible. Therefore, the spirit and scope of the appended claims should not be limited to the description of the embodiments contained herein.

It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present disclosure without departing from the scope or spirit of the disclosure. In view of the foregoing, it is intended that the present disclosure cover modifications and variations of this disclosure provided they fall within the scope of the following claims.