FORWARD CONVERTER AND FORWARD POWER FACTOR CORRECTOR

A forward converter includes a voltage conversion device, a switch and an auxiliary device. The voltage conversion device includes a primary winding and a secondary winding, and is configured to convert an input voltage into an output voltage. The switch is connected to the voltage conversion device, and is switched to make the voltage conversion device receive or not receive the input voltage. The auxiliary device is connected to the voltage conversion device. When the switch is cut off, the auxiliary device stores electrical energy released by the voltage conversion device and generates a compensation voltage, and when the switch is turned on, the auxiliary device provides the compensation voltage, wherein the compensation voltage and the input voltage have same polarity. The present disclosure further provides a forward power factor corrector including the forward converter described above and a rectifying device.

BACKGROUND

1. Technical Field

This disclosure relates to a forward converter and forward power factor corrector.

2. Related Art

At present, many electrical appliances use low-voltage direct current. However, since power provided by the supply mains is alternating current (AC), alternating current-direct current conversion is required. In order to reduce the reactive power of the power system and reduce the system interference caused by current harmonics, many electrical appliances are required to have high power factor and low current harmonics, so power factor correctors are widely used.

Based on safety and performance considerations, power factor correctors are required to have high power factor, high conversion efficiency and electrical isolation. Conventional circuit structures such as fly-back structure have poor conversion efficiency; and for conventional forward circuits, when the input AC power is in a low voltage state, if the induced voltage on the secondary side is less than the output voltage of the power factor corrector, the input current cannot be introduced, resulting in a current dead zone. Therefore, the power factor correction effect is compromised, and additional transformer is needed to deal with demagnetization requirement. Other conventional technologies and circuit structures also face different technical bottlenecks and cannot meet increasingly stringent regulatory requirements.

SUMMARY

According to one or more embodiment of this disclosure, a forward converter includes a voltage conversion device, a switch and an auxiliary device. The voltage conversion device includes a primary winding and a secondary winding and is configured to convert an input voltage into an output voltage. The switch is connected to the voltage conversion device and is configured to be switched to make the voltage conversion device receive or not receive the input voltage. The auxiliary device is connected to the voltage conversion device, stores electrical energy released by the voltage conversion device and generating a compensation voltage when the switch is cut off, and providing the compensation voltage when the switch is turned on, wherein the compensation voltage and the input voltage have same polarity.

According to one or more embodiment of this disclosure, a forward power factor corrector includes the forward converter described above and a rectifying device connected to the forward converter and configured to receive and rectify a power source to generate the input voltage.

DETAILED DESCRIPTION

In the following detailed description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the disclosed embodiments. According to the description, claims and the drawings disclosed in the specification, one skilled in the art may easily understand the concepts and features of the present invention. The following embodiments further illustrate various aspects of the present invention, but are not meant to limit the scope of the present invention.

Please refer toFIG.1, whereinFIG.1is a block diagram illustrating a forward converter according to an embodiment of the present disclosure. As shown inFIG.1, the forward converter1includes a switch10, a voltage conversion device20and an auxiliary device30. The switch10is connected to the voltage conversion device20, and the voltage conversion device20is connected to the auxiliary device30.

The switch10is configured to be switched to make the voltage conversion device20receive or not receive an input voltage. For example, the switch10may be an active power switch element, and is configured to be triggered to be cut off or turned on, so that the voltage conversion device20receives or does not receive the input voltage.

The voltage conversion device20includes a primary winding201and a secondary winding202, and the voltage conversion device20is configured to convert the input voltage into the output voltage. The primary winding201and the secondary winding202each includes one or more coils. In an implementation, the voltage conversion device20may further include a fly wheeling diode, an energy storage inductor and an output capacitor. A first terminal of the energy storage inductor may be configured to output the output voltage. A cathode of the fly wheeling diode and a second terminal of the energy storage inductor may be commonly connected to a first node, and the first node may be connected to the auxiliary device30. A terminal of the output capacitor may be connected to another terminal of the energy storage inductor, and another terminal of the output capacitor may be connected to an anode of the fly wheeling diode.

The auxiliary device30may include one or more passive elements. A terminal of the auxiliary device30is connected to the secondary winding202, and another terminal of the auxiliary device30is connected to the second terminal of the energy storage inductor of the voltage conversion device20. Alternatively, a terminal of the auxiliary device30may be configured to receive the input voltage, and another terminal of the auxiliary device30is connected to the primary winding201. When the switch10is cut off, the auxiliary device30stores energy released by the voltage conversion device20and generates a compensation voltage; and when the switch10is turned on, the auxiliary device30provides the compensation voltage, wherein the compensation voltage and the input voltage have same polarity.

By storing energy released by the voltage conversion device when the switch is cut off and generating the compensation voltage, the forward converter may have the function of demagnetization and may provide the compensation voltage when the switch is turned on. Specifically, in the application of an alternating current input, the compensation voltage may ease the situation of current dead zone.

Please refer toFIG.2, whereinFIG.2is a block diagram illustrating a forward power factor corrector according to an embodiment of the present disclosure. As shown inFIG.2, the forward power factor corrector100includes a forward converter1and a rectifying device2. The forward converter1may be the forward converter1shown inFIG.1. The rectifying device2is connected to a power source Vsand the forward converter1. The rectifying device2is configured to receive and rectify the power source Vsto generate the input voltage described above. Specifically, the power source Vsmay provide alternating current, the alternating current is converted into a direct current by the rectifying device2, and the direct current is provided to the forward converter1. The forward converter1converts the input voltage into the output voltage Vo, wherein the output voltage Vomay be output to a load connected to the forward converter1.

Please refer toFIG.3, whereinFIG.3is a block diagram illustrating a forward power factor corrector according to another embodiment of the present disclosure. As shown inFIG.3, the forward power factor corrector100′ includes a forward converter1, a rectifying device2and a filtering device3. The rectifying device2is connected to the forward converter1and the filtering device3, wherein the connection and operation of the forward converter1and the rectifying device2are the same as the embodiment described above, and their detail descriptions are not repeated herein. In this embodiment, the filtering device3is connected between the rectifying device2and the power source Vs, to first filter the alternating current and then transmit the filtered alternating current to the rectifying device2to perform alternating current-direct current conversion.

To further explain circuits of the filtering device3and the rectifying device2, please refer toFIG.4, whereinFIG.4exemplarily illustrates circuit diagrams of the rectifying device2and the filtering device3included in the forward power factor corrector100′ ofFIG.3. As shown inFIG.4, the rectifying device2may include a first diode D21, a second diode D22, a third diode D23and a fourth diode D24. An anode of the first diode D21is connected to a cathode of the third diode D23. A cathode of the first diode D21is connected to a cathode of the second diode D22. An anode of the second diode D22is connected to a cathode of the fourth diode D24. An anode of the third diode D23is connected to an anode of the fourth diode D24. The filtering device3may include a capacitor Dfand an inductor Lf. A first terminal of the capacitor Dfis connected to a first terminal of the inductor Lf, an anode of the first diode D21and a cathode of the third diode D23. A second terminal of the capacitor Dfis connected to the power source Vs, an anode of the second diode D22and a cathode of the fourth diode D24. A second terminal of the inductor Lfis connected to the power source Vs.

The filtering device3is configured to receive and filter the power source Vsto generate the filtered power source Vs. The rectifying device2is configured to receive and rectify the filtered power source Vsto form the input voltage Vibetween the cathode of the second diode D22and the anode of the fourth diode D24. The forward converter1converts the input voltage Viinto the output voltage Vo, wherein the output voltage Vomay be output to a load connected to the forward converter1. It should be noted thatFIG.4illustrates the basic circuit for implementing the rectifying device2and the filtering device3,FIG.4does not intend to limit that the rectifying device2and the filtering device3can only be implemented by the circuit structure shown inFIG.4. In addition, the filtering device3shown inFIG.4is selectively disposed.

The following further explains embodiments for implementing the forward converter1described above. Please refer toFIG.5, whereinFIG.5is a circuit diagram of illustrating the forward converter according to a first embodiment of the present disclosure. As shown inFIG.5, the forward converter1_1includes a switch10_1, a voltage conversion device20_1and an auxiliary device30_1.

The switch10_1includes an active power switch element Q1. The voltage conversion device20_1includes a primary winding N1and a secondary winding N2, the fly wheeling diode D1as described above, an energy storage inductor L1and an output capacitor C1. The auxiliary device30_1includes an auxiliary capacitor Ca.

Specifically, the first terminal of the energy storage inductor L1is configured to output the output voltage Vo, and the second terminal of the energy storage inductor L1is connected to the cathode of the fly wheeling diode D1. A terminal of the auxiliary capacitor Ca of the auxiliary device30_1is connected to the secondary winding N2, and another terminal of the auxiliary capacitor Ca is connected to the second terminal of the energy storage inductor L1and the cathode of the fly wheeling diode D1.

Please refer toFIG.5along withFIG.6AtoFIG.6C, whereinFIG.6AtoFIG.6Cillustrate a first operation mode, a second operation mode and a third operation mode of the forward converter ofFIG.5, respectively.

Please refer toFIG.6A, in the first operation mode, the active power switch element Q1is turned on, and the fly wheeling diode D1is cut off. When the active power switch element Q1is turned on, the input voltage Viis provided to the primary winding N1of the voltage conversion device20_1, the induced voltage of the secondary winding N2and the compensation voltage Vcaof the auxiliary capacitor Ca of the voltage conversion device20_1both charge the output capacitor C1. At the same time, the energy storage inductor L1stores energy, the auxiliary capacitor Ca is in a discharge state. This operation mode continues until the active power switch element Q1is cut off, and the second operation mode is entered.

Please refer toFIG.6B, in the second operation mode, the active power switch element Q1is cut off, and the fly wheeling diode D1is turned on. The magnetized secondary winding N2may be demagnetized through the path formed from the fly wheeling diode D1to the auxiliary capacitor Ca, and the auxiliary capacitor Ca may be charged to build the compensation voltage Vca. The energy storage inductor L1may release energy through the path formed from the output capacitor C1and the fly wheeling diode D1. This operation mode continues until the secondary winding N2and the energy storage inductor L1discharge all energy, and the third operation mode is entered.

Please refer toFIG.6C, in the third operation mode, the active power switch element Q1and the fly wheeling diode D1are cut off, the forward converter does not perform conversion. The energy stored by the output capacitor C1may continue to provide current to the load. Then, when the active power switch element Q1is turned on again, the energy stored by the auxiliary capacitor Ca is used to charge the output capacitor C1. That is, the forward converter1_1returns to the first operation mode ofFIG.6A. In particular, in an application where the forward converter of this embodiment is designed to operate in continuous current mode, the third operation mode may not need to exist. That is, after the second operation mode, the operation may directly return to the first operation mode.

Please refer toFIG.7, whereinFIG.7is a circuit diagram of illustrating the forward converter according to a second embodiment of the present disclosure. As shown inFIG.7, the forward converter1_2includes a switch10_2, a voltage conversion device20_2and an auxiliary device30_2, wherein circuit/device implementations, functions and connections of the switch10_2and the voltage conversion device20_2may all be the same as the switch10_1and the voltage conversion device20_1included in the forward converter1_1ofFIG.5.

The auxiliary device30_2includes an auxiliary capacitor Ca, an auxiliary diode Da1and an auxiliary winding La1. An anode of the auxiliary diode Da1is connected to the first terminal of the auxiliary capacitor Ca. The auxiliary winding La1is inductively coupled to the energy storage inductor L1of the voltage conversion device20_2. A terminal of the auxiliary winding La1is connected to the cathode of the auxiliary diode Da1, and another terminal of the auxiliary winding La1is connected to the second terminal of the auxiliary capacitor Ca.

Please refer toFIG.7andFIG.8AtoFIG.8D, whereinFIG.8AtoFIG.8Dillustrate a first operation mode, a second operation mode, a third operation mode and a fourth operation mode of the forward converter ofFIG.7, respectively.

Please refer toFIG.8A, in the first operation mode, the active power switch element Q1is turned on, the auxiliary diode Da1is cut off, the fly wheeling diode D1is cut off. When the active power switch element Q1is turned on, the input voltage Viis provided to the primary winding N1of the voltage conversion device20_2. The induced voltage of the secondary winding N2and the compensation voltage Vcaof the auxiliary capacitor Ca of the voltage conversion device20_2both charge the output capacitor C1. At the same time, the energy storage inductor L1stores energy, the auxiliary capacitor Ca is in a discharge state, and the compensation voltage Vcadeceases. This operation mode continues until the active power switch element Q1is cut off, and the second operation mode is entered.

Please refer toFIG.8B, in the second operation mode, the active power switch element Q1is cut off, the auxiliary diode Da1is turned on, the fly wheeling diode D1is cut off. The magnetized secondary winding N2may be demagnetized through the path formed from the auxiliary diode Da1to the auxiliary capacitor Ca, and the auxiliary capacitor Ca may be charged to build the compensation voltage Vca, and the compensation voltage Vcaincreases. The energy storage inductor L1may discharge stored energy to the auxiliary capacitor Ca through the auxiliary winding La1. This operation mode continues until the compensation voltage Vcais equal to the first mapped voltage, and the third operation mode is entered. The first mapped voltage is an equivalent voltage of the output voltage Vomapped to the auxiliary winding La1side according to a turn ratio of the energy storage inductor L1and the auxiliary winding La1.

Please refer toFIG.8C, in the third operation mode, the active power switch element Q1is cut off, the auxiliary diode Da1is cut off, the fly wheeling diode D1is turned on. The magnetized secondary winding N2is continuously demagnetized through the path formed from the fly wheeling diode D1to the auxiliary capacitor Ca, and the auxiliary capacitor Ca may be charged to build the compensation voltage Vca. The inductor L1releases the stored energy through the path formed by the fly wheeling diode D1and the output capacitor C1. This operation mode continues until all energy stored in the energy storage inductor L1and the magnetized secondary winding N2is released, and the fourth operation mode is entered.

Please refer toFIG.8D, in the fourth operation mode, the active power switch element Q1, the fly wheeling diode D1and the auxiliary diode Da1are cut off, and the forward converter does not perform conversion. The energy stored by the output capacitor C1may continue to provide current to the load. Then, when the active power switch element Q1is turned on again, energy stored by the auxiliary capacitor Ca is used to charge the output capacitor C1. That is, the forward converter1_2returns to the first operation mode ofFIG.8A. In particular, in an application where the forward converter of this embodiment is designed to operate in continuous current mode, the fourth operation mode may not need to exist. That is, after the third operation mode, the operation may directly return to the first operation mode.

Please refer toFIG.9, whereinFIG.9is a circuit diagram of illustrating the forward converter according to a third embodiment of the present disclosure. As shown inFIG.9, the forward converter1_3includes a switch10_3, a voltage conversion device20_3and an auxiliary device30_3, wherein circuit/device implementations, functions and connections of the switch10_3and the voltage conversion device20_3may all be the same as the switch10_1and the voltage conversion device20_1included in the forward converter1_1ofFIG.5, and their detail descriptions are not repeated herein.

The auxiliary device30_2includes an auxiliary capacitor Ca, an auxiliary diode Da2and an auxiliary winding La2. An anode of the auxiliary diode Da2is connected to the first terminal of the auxiliary capacitor Ca. The auxiliary winding La2is inductively coupled to the primary winding N1and the secondary winding N2. A terminal of the auxiliary winding La2is connected to the cathode of the auxiliary diode Da2, and another terminal of the auxiliary winding La2is connected to the second terminal of the auxiliary capacitor Ca.

Please refer toFIG.9andFIG.10AtoFIG.10C, whereinFIG.10AtoFIG.10Cillustrate a first operation mode, a second operation mode and a third operation mode of the forward converter ofFIG.9, respectively.

Please refer toFIG.10A, in the first operation mode, the active power switch element Q1is turned on, the auxiliary diode Da2is cut off, the fly wheeling diode D1is cut off. When the active power switch element Q1is turned on, the input voltage Viis provided to the primary winding N1of the voltage conversion device20_3. The induced voltage of the secondary winding N2and the compensation voltage Vcaof the auxiliary capacitor Ca of the voltage conversion device20_3both charge the output capacitor C1. At the same time, the energy storage inductor L1stores energy, the auxiliary capacitor Ca is in a discharge state. This operation mode continues until the active power switch element Q1is cut off, and the second operation mode is entered.

Please refer toFIG.10B, in the second operation mode, the active power switch element Q1is cut off, the auxiliary diode Da2is turned on, the fly wheeling diode D1is cut off. Since the auxiliary winding La2is inductively coupled to the primary winding N1and the secondary winding N2, energy stored by the primary winding N1and the secondary winding N2may be released through the auxiliary winding La2to perform demagnetization, and the auxiliary capacitor Ca may be charged to build the compensation voltage Vca. The energy storage inductor L1may release energy through the path formed by the output capacitor C1and the fly wheeling diode D1. This operation mode continues until said demagnetization is completed, and the energy storage inductor L1releases all energy. In particular, in some implementations, the demagnetization performed by the auxiliary winding La2through the auxiliary diode Da2and the auxiliary capacitor Ca and the energy release performed by the energy storage inductor L1through the output capacitor C1and the fly wheeling diode D1may be completed at different timings. When the demagnetization of the auxiliary winding La2and the energy release of the energy storage inductor L1are both completed, the auxiliary device30_2enters the third operation mode.

Please refer toFIG.10C, in the third operation mode, since energy stored by the energy storage inductor L1is completely released, the current on the energy storage inductor L1is reduced to zero, and after energy is completely released from the magnetized secondary winding N2in the second operation mode, the current on the auxiliary capacitor Ca is reduced to zero, and the fly wheeling diode D1and the auxiliary diode Da2both enter the cut-off state, and the active power switch element Q1is still in the cut-off state. The energy stored by the output capacitor C1may continue to provide current to the load. When the active power switch element Q1is triggered to be turned on again, energy stored by the auxiliary capacitor Ca is used to charge the output capacitor C1. That is, the forward converter1_3returns to the first operation mode. In particular, in the application where the forward converter of this embodiment is designed to operate in continuous current mode, the third operation mode may not need to exist. That is, after the second operation mode, the operation may directly return to the first operation mode.

Please refer toFIG.11, whereinFIG.11is a circuit diagram of illustrating the forward converter according to a fourth embodiment of the present disclosure. As shown inFIG.11, the forward converter1_4includes a switch10_4, a voltage conversion device20_4and an auxiliary device30_4, wherein circuit/device implementations, functions and connections of the switch10_4may all be the same as that of the switch10_1included in the forward converter1_1ofFIG.5, and circuit/device implementations, functions and connections of the voltage conversion device20_4may all be the same as that of the voltage conversion device20_2included in the forward converter1_2ofFIG.7, and their detail descriptions are not repeated herein.

The auxiliary device30_4includes an auxiliary capacitor Ca, a first auxiliary diode Da2, a first auxiliary winding La2, a second auxiliary diode Da3and a second auxiliary winding La3. An anode of the first auxiliary diode Da2is connected to the first terminal of the auxiliary capacitor Ca. The first auxiliary winding La2is inductively coupled to the primary winding N1and the secondary winding N2, wherein a terminal of the first auxiliary winding La2is connected to a cathode of the first auxiliary diode Da2, and another terminal of the first auxiliary winding La2is connected to the second terminal of the auxiliary capacitor Ca. An anode of the second auxiliary diode Da3is connected to the first terminal of the auxiliary capacitor Ca. A terminal of the second auxiliary winding La3is connected to a cathode of the second auxiliary diode Da3, and another terminal of the second auxiliary winding La3is connected to the second terminal of the auxiliary capacitor Ca. The second auxiliary winding La3is inductively coupled to the energy storage inductor L1.

Please refer toFIG.11andFIG.12AtoFIG.12D, whereinFIG.12AtoFIG.12Dillustrate a first operation mode, a second operation mode, a third operation mode and a fourth operation mode of the forward converter ofFIG.11, respectively.

Please refer toFIG.12A, in the first operation mode, the active power switch element Q1is turned on, the first auxiliary diode Da2is cut off, the second auxiliary diode Da3is cut off, and the fly wheeling diode D1is cut off. When the active power switch element Q1is turned on, the input voltage Viis provided to the primary winding N1of the voltage conversion device20_4. The induced voltage of the secondary winding N2and the compensation voltage Vcaof the auxiliary capacitor Ca of voltage conversion device20_4both charge the output capacitor C1. At the same time, the energy storage inductor L1stores energy, the auxiliary capacitor Ca is in a discharge state. This operation mode continues until the active power switch element Q1is cut off, and the second operation mode is entered.

Please refer toFIG.12B, in the second operation mode, the active power switch element Q1is cut off, the first auxiliary diode Da2is turned on, the second auxiliary diode Da3is turned on, the fly wheeling diode D1is cut off. Since the first auxiliary winding La2is inductively coupled to the primary winding N1and the secondary winding N2, by the inductor inductively coupled to the first auxiliary winding La2, the magnetized secondary winding N2may release energy through the path formed from the first auxiliary diode Da2to the auxiliary capacitor Ca to perform the demagnetization, and the auxiliary capacitor Ca may be charged to build the compensation voltage Vca. Since the second auxiliary winding La3is inductively coupled to the energy storage inductor L1, energy stored by the energy storage inductor L1may be released from the second auxiliary winding La3to charge the auxiliary capacitor Ca. Therefore, the compensation voltage Vcaincreases. This operation mode continues until the compensation voltage Vcais equal to the second mapped voltage, and the third operation mode is entered. The second mapped voltage is an equivalent voltage of the output voltage Vomapped to the second auxiliary winding La3side according to a turn ratio of the energy storage inductor L1and the second auxiliary winding La3.

Please refer toFIG.12C, in the third operation mode, the active power switch element Q1is cut off, the first auxiliary diode Da2is turned on, the second auxiliary diode Da3is cut off, and the fly wheeling diode D1is turned on. The magnetized secondary winding N2continues to perform the demagnetization through the path formed from the first auxiliary diode Da2to the auxiliary capacitor Ca, and continues to charge the auxiliary capacitor Ca to build the compensation voltage Vca. The energy storage inductor L1continues to release energy to charge the output capacitor C1. This operation mode continues until the magnetized secondary winding N2and energy stored by the energy storage inductor L1is completely released, and the fourth operation mode is entered.

Please refer toFIG.12D, after the magnetized secondary winding N2and the energy storage inductor L1completely releases the stored energy in the third operation mode, the currents on the auxiliary capacitor Ca and the energy storage inductor L1are reduced to zero, and the first auxiliary diode Da2, the second auxiliary diode Da3and the fly wheeling diode D1are all in the cut-off state. The energy stored by the output capacitor C1may continue to provide current to the load. When the active power switch element Q1is triggered to be turned on again, energy stored by the auxiliary capacitor Ca is used to charge the output capacitor C1. That is, the forward converter1_4returns to the first operation mode. In particular, in an application where the forward converter of this embodiment is designed to operate in continuous current mode, the fourth operation mode may not need to exist. That is, after the third operation mode, the operation may directly return to the first operation mode.

Please refer toFIG.13, whereinFIG.13is a circuit diagram of illustrating the forward converter according to a fifth embodiment of the present disclosure. As shown inFIG.13, the forward converter1_5includes a switch10_5, a voltage conversion device20_5and an auxiliary device30_5, wherein circuit/device implementations and functions of the switch10_5may all be the same as that of the switch10_1included in the forward converter1_1ofFIG.5, and their detail descriptions are not repeated herein.

In addition to the elements of the voltage conversion device20_1shown inFIG.5, the voltage conversion device20_5of the forward converter1_5further includes another fly wheeling diode D2. An anode of the fly wheeling diode D2is connected to the secondary winding N2, and a cathode of the fly wheeling diode D2is connected to the second terminal of the energy storage inductor L1.

The auxiliary device30_5is disposed at the primary side of the forward converter1_5. Furthermore, a terminal of the auxiliary device30_5is configured to receive the input voltage Vi, and another terminal of the auxiliary device30_5is connected to the primary winding N1. The auxiliary device30_5includes an auxiliary capacitor Ca, an auxiliary diode Da4and an auxiliary winding La4. The first terminal of the auxiliary capacitor Ca is configured to receive the input voltage Vi, and the second terminal of the auxiliary capacitor Ca is connected to the primary winding N1. An anode of the auxiliary diode Da4is connected to the first terminal of the auxiliary capacitor Ca. The auxiliary winding La4is inductively coupled to the primary winding N1and the secondary winding N2, wherein a terminal of the auxiliary winding La4is connected to a cathode of the auxiliary diode Da4, and another terminal of the auxiliary winding La4is connected to the second terminal of the auxiliary capacitor Ca.

Please refer toFIG.13andFIG.14AtoFIG.14C, whereinFIG.14AtoFIG.14Cillustrate a first operation mode, a second operation mode and a third operation mode of the forward converter ofFIG.13, respectively.

Please refer toFIG.14A, in the first operation mode, the active power switch element Q1is turned on, the auxiliary diode Da4is cut off, the fly wheeling diode D1is cut off, and the fly wheeling diode D2is turned on. When the active power switch element Q1is turned on, the input voltage Viand the auxiliary capacitor Ca charge the primary winding N1of the voltage conversion device20_5. The induced voltage of the secondary winding N2of the voltage conversion device20_5charges the output capacitor C1through the fly wheeling diode D2. At the same time, the energy storage inductor L1stores energy, the auxiliary capacitor Ca is in a discharge state. This operation mode continues until the active power switch element Q1is cut off, and the second operation mode is entered.

Please refer toFIG.14B, in the second operation mode, the active power switch element Q1is cut off, the auxiliary diode Da4is turned on, the fly wheeling diode D1is turned on, and the fly wheeling diode D2is cut off. Since the auxiliary winding La4is inductively coupled to the primary winding N1and the secondary winding N2, energy stored by the primary winding N1and the secondary winding N2may be released from the auxiliary winding La4to perform the demagnetization, and the auxiliary capacitor Ca may be charged to build the compensation voltage Vca. The energy storage inductor L1may release energy through the path formed from the output capacitor C1and the fly wheeling diode D1. This operation mode continues until said demagnetization is completed, and the energy storage inductor L1releases all energy. In particular, in some implementations, the demagnetization performed by the auxiliary winding La4through the auxiliary diode Da4and the auxiliary capacitor Ca and the energy release performed by the energy storage inductor L1through the output capacitor C1and the fly wheeling diode D1may be completed at different timings. When the demagnetization of the auxiliary winding La4and the energy release of the energy storage inductor L1are both completed, the auxiliary device30_5enters the third operation mode.

Please refer toFIG.14C, in the third operation mode, energy stored in the primary winding N1and the secondary winding N2is completely released, and energy stored in the energy storage inductor L1is completely released in the second operation mode, the current on the energy storage inductor L1is reduced to zero, the active power switch element Q1, the fly wheeling diodes D1and D2and the auxiliary diode Da4all enter the cut-off state. When the active power switch element Q1is triggered to be turned on again, energy stored by the auxiliary capacitor Ca is used to charge the output capacitor C1. That is, the forward converter1_5returns to the first operation mode. The energy stored by the output capacitor C1may continue to provide current to the load. In particular, in an application where the forward converter of this embodiment is designed to operate in continuous current mode, the third operation mode may not need to exist. That is, after the second operation mode, the operation may directly return to the first operation mode.

Please refer toFIG.15, whereinFIG.15is a circuit diagram of illustrating the forward converter according to a sixth embodiment of the present disclosure. As shown inFIG.15, the forward converter1_6includes a switch10_6, a voltage conversion device20_6and an auxiliary device30_6, wherein circuit/device implementations and functions of the switch10_6and the voltage conversion device20_6are the same as that of the switch10_5and the voltage conversion device20_5included in the forward converter1_5ofFIG.13, and their detail descriptions are not repeated herein.

The auxiliary device30_6is disposed at the primary side of the forward converter1_6. The auxiliary device30_6includes an auxiliary capacitor Ca, a first auxiliary diode Da4, a second auxiliary diode Da5, a first auxiliary winding La4and a second auxiliary winding La5. The first terminal of the auxiliary capacitor Ca is configured to receive the input voltage Vi, and the second terminal of the auxiliary capacitor Ca is connected to the primary winding N1. An anode of the first auxiliary diode Da4is connected to the first terminal of the auxiliary capacitor Ca. The first auxiliary winding La4is inductively coupled to the primary winding N1and the secondary winding N2. A terminal of the first auxiliary winding La4is connected to a cathode of the first auxiliary diode Da4, and another terminal of the first auxiliary winding La4is connected to the second terminal of the auxiliary capacitor Ca. An anode of the second auxiliary diode Da5is connected to the first terminal of the auxiliary capacitor Ca. The second auxiliary winding La5is inductively coupled to the energy storage inductor L1. A terminal of the second auxiliary winding La5is connected to a cathode of the second auxiliary diode Da5, and another terminal of the second auxiliary winding La5is connected to the second terminal of the auxiliary capacitor Ca.

Please refer toFIG.15andFIG.16AtoFIG.16D, whereinFIG.16AtoFIG.16Dillustrate a first operation mode, a second operation mode, a third operation mode and a fourth operation mode of the forward converter ofFIG.15, respectively.

Please refer toFIG.16A, in the first operation mode, the active power switch element Q1is turned on, the first auxiliary diode Da4is cut off, the second auxiliary diode Da5is cut off, the fly wheeling diode D1is cut off, and the fly wheeling diode D2is turned on. When the active power switch element Q1is turned on, the input voltage Viand the auxiliary capacitor Ca charge the primary winding N1of the voltage conversion device20_6. The induced voltage of the secondary winding N2of the voltage conversion device20_6charges the output capacitor C1. At the same time, the energy storage inductor L1stores energy, the auxiliary capacitor Ca is in a discharge state. This operation mode continues until the active power switch element Q1is cut off, and the second operation mode is entered.

Please refer toFIG.16B, in the second operation mode, the active power switch element Q1is cut off, the first auxiliary diode Da4is turned on, the second auxiliary diode Da5is turned on, the fly wheeling diodes D1and D2are cut off. After the active power switch element Q1is cut off, since the first auxiliary winding La4is inductively coupled to the primary winding N1and the secondary winding N2, energy stored by the primary winding N1and the secondary winding N2may be used to perform the demagnetization through the path formed from the first auxiliary diode Da4to the auxiliary capacitor Ca, and the auxiliary capacitor Ca may be charged to build the compensation voltage Vca. Since the second auxiliary winding La5is inductively coupled to the energy storage inductor L1, energy stored by the energy storage inductor L1may charge the auxiliary capacitor Ca through the second auxiliary winding La5by the path formed from the second auxiliary diode Da5to the auxiliary capacitor Ca to build the compensation voltage Vca. Therefore, the compensation voltage Vcaincreases. This operation mode continues until the compensation voltage Vcais equal to the third mapped voltage, and the third operation mode is entered. The third mapped voltage is an equivalent voltage of the output voltage Vomapped to the second auxiliary winding La5side according to a turn ratio of the energy storage inductor L1and the second auxiliary winding La5.

Please refer toFIG.16C, in the third operation mode, the active power switch element Q1is cut off, the first auxiliary diode Da4is turned on, the second auxiliary diode Da5is cut off, the fly wheeling diode D1is turned on, and the fly wheeling diode D2is cut off. The first auxiliary winding La4continues to perform the demagnetization through the path formed from the first auxiliary diode Da4to the auxiliary capacitor Ca, and continues to charge the auxiliary capacitor Ca to build the compensation voltage Vca. Energy stored by the energy storage inductor L1is released through the fly wheeling diode D1to charge the output capacitor C1. This operation mode continues until energy stored by the first auxiliary winding La4and the energy storage inductor L1is completely released, and the fourth operation mode is entered.

Please refer toFIG.16D, after energy stored in the first auxiliary winding La4and the energy storage inductor L1is completely released in the third operation mode, the currents on the auxiliary capacitor Ca and the energy storage inductor L1are reduced to zero, and the first auxiliary diode Da4, the second auxiliary diode Da5and the fly wheeling diodes D1and D2all enter the cut-off state, and the active power switch element Q1is still in the cut-off state. The energy stored by the output capacitor C1may continue to provide current to the load. When the active power switch element Q1is triggered to be turned on again, energy stored by the auxiliary capacitor Ca is used to charge the output capacitor C1. That is, the forward converter1_6returns to the first operation mode. In particular, in an application where the forward converter of this embodiment is designed to operate in continuous current mode, the fourth operation mode may not need to exist. That is, after the third operation mode, the operation may directly return to the first operation mode.

It may be known from the above embodiments that the forward converter and the auxiliary device of the present disclosure may be summarized into various implementations as follows. In the first implementation, the forward converter and the auxiliary device include the auxiliary capacitor. In the second implementation, the auxiliary device includes the auxiliary capacitor, the auxiliary diode and the auxiliary winding, wherein the anode of the auxiliary diode is connected to the first terminal of the auxiliary capacitor, the auxiliary winding is inductively coupled to the primary winding and the secondary winding, and a terminal of the auxiliary winding is connected to the cathode of the auxiliary diode, and another terminal of the auxiliary winding is connected to the second terminal of the auxiliary capacitor. In the third implementation, the voltage conversion device further includes the energy storage inductor configured to output the output voltage, and the auxiliary device includes the auxiliary capacitor, the auxiliary diode and the auxiliary winding, wherein the anode of the auxiliary diode is connected to the first terminal of the auxiliary capacitor, the auxiliary winding is inductively coupled to the energy storage inductor, a terminal of the auxiliary winding is connected to the cathode of the auxiliary diode, and another terminal of the auxiliary winding is connected to the second terminal of the auxiliary capacitor. In the fourth implementation, the voltage conversion device further includes the energy storage inductor configured to output the output voltage, and the auxiliary device includes the auxiliary capacitor, the first auxiliary diode, the second auxiliary diode, the first auxiliary winding and the second auxiliary winding, the anode of the first auxiliary diode is connected to the first terminal of the auxiliary capacitor, the first auxiliary winding is inductively coupled to the primary winding and the secondary winding, a terminal of the first auxiliary winding is connected to the cathode of the first auxiliary diode, another terminal of the first auxiliary winding is connected to the second terminal of the auxiliary capacitor, the anode of the second auxiliary diode is connected to the first terminal of the auxiliary capacitor, the second auxiliary winding is inductively coupled to the energy storage inductor, a terminal of the second auxiliary winding is connected to the cathode of the second auxiliary diode, and another terminal of the second auxiliary winding is connected to the second terminal of the auxiliary capacitor.

The auxiliary device of the above implementations may be connected to the primary winding or the secondary winding, wherein the primary winding is especially adapted to the second implementation to the fourth implementation. It should be noted that by connecting the auxiliary device to the secondary winding, a diode may not need to be disposed between the energy storage inductor and the secondary winding of the voltage conversion device of the forward converter. Therefore, comparing to the structure of the auxiliary device connected to the primary winding, the present disclosure may have a simpler circuit structure.

Please refer toFIG.17, whereinFIG.17exemplarily presents the waveform diagrams of the voltage and the current at an alternating-current (AC) input terminal the secondary-side current of the forward power factor corrector of the forward converter according to an embodiment of the present disclosure. As shown inFIG.17, the voltage Vs at the AC input terminal and the current Is at the AC input terminal match each other, there is low current harmonics. In addition, according to a demagnetization interval d1of the secondary-side current I2, it may be known that the forward power factor corrector may effectively perform demagnetization.

Please refer toFIG.18, whereinFIG.18exemplarily presents relationship between duty cycle of the switch and the output voltage of the forward power factor corrector according to an embodiment of the present disclosure. The relationship between the duty cycle of the switch and the output voltage of the output voltage may be presented with the following equation 1:

wherein Vois the output voltage, Vsis the voltage of the AC input, as shown inFIG.2, and D is the duty cycle of the switch.

In view of the above description, with the auxiliary device, the forward converter according to one or more embodiments of the present disclosure may have the advantages of high conversion efficiency, meet the demagnetization requirements of the windings of a voltage converter, be able to provide compensation voltage, be smaller in size and light in weight, and may do so without adding additional complex and high-cost structure. The forward power factor corrector including the forward converter described above of the present disclosure, in addition to the above advantageous, may also reduce the current dead zone through the compensation voltage of the auxiliary device, and may achieve the effects of high power factor and low harmonic rate.