TWM641099U - Dual Mode Active Clamp Forward Converter - Google Patents

Abstract

A dual-mode active clamp forward converter includes a transformer circuit, a clamp energy storage circuit and a main switch circuit. The transformer circuit includes an auxiliary winding, a capacitor, and a primary winding. When the load is heavy, the clamping energy storage circuit is turned on and then turned off; when the load is light, the clamping energy storage circuit remains off. When the main switching circuit is turned on, the auxiliary winding discharges energy to the primary side winding. After the clamping energy storage circuit is turned on and then turned off, the main switch circuit enters zero-voltage switching. When the value of the actual output power is smaller than the value of the output power corresponding to the turning point of the conversion efficiency, the load is a light load. When the value of the actual output power is greater than the value of the output power corresponding to the turning point of the conversion efficiency, the load is heavy.

Description

Dual Mode Active Clamp Forward Converter

The invention relates to a dual-mode active-clamp forward converter, especially a dual-mode active-clamp forward converter that can automatically switch operation modes for optimum efficiency corresponding to heavy load or light load.

The forward converter (forward converter) is widely used in medium and low power power conversion systems because of its simple circuit structure, and has the advantages of electrical isolation and adjustable output voltage through the turn ratio. However, due to the existence of transformer leakage inductance, when the switch turns on the primary side magnetizing inductance to store energy, the leakage inductance will also store energy. When the switch cuts off the magnetizing inductance and starts to discharge energy to the secondary side, if there is no release path for the energy of the leakage inductance, it will release energy to the capacitance Cds of the power switch (that is, the parasitic capacitance between the drain and the source), making the drain -The voltage Vds between the sources rises sharply, and a rather high surge voltage appears, causing damage to the power switch. In recent years, in order to improve the above problems, active clamping techniques have been proposed one after another.

As shown in FIG. 1 , it is a circuit diagram of an existing active-clamp forward converter. The leakage inductance energy in the transformer winding can be stored by clamping capacitor Cd, and the energy can be recovered to the input end. As shown in FIG. 2 , it is a circuit diagram of an existing passive forward converter with leakage inductance energy recovery function. The clamp capacitor C1 can store the leakage inductance energy in the transformer winding, and recover the temporarily stored leakage inductance energy to the input terminal during the conduction period of the main switch Q.

The efficiency characteristics of the above two architectures are: the active clamp forward converter in Figure 1 operates under low input voltage and heavy load conditions, and has high conversion efficiency, but when it operates under high input voltage and light load, its conversion efficiency Obviously far inferior to the passive forward converter of Fig. 2.

For this reason, how to design a dual-mode active clamp forward converter, especially a dual-mode active clamp forward converter that can automatically switch the operating mode for optimal efficiency corresponding to heavy load or light load, solves the existing The problems and technical bottlenecks in technology are the important subjects studied by the author of this case.

The purpose of this creation is to provide a dual-mode active clamp forward converter to solve the problems in the prior art.

To achieve the purpose of the foregoing disclosure, the dual-mode active clamp forward converter proposed in this work includes a transformer circuit, a clamp energy storage circuit and a main switch circuit. The transformer circuit is coupled to a load and includes an auxiliary winding, a capacitor and a primary winding. The clamping energy storage circuit is coupled to the transformer circuit. When the load is heavy, the clamping energy storage circuit is turned on and then turned off; when the load is light, the clamping energy storage circuit remains off. The main switch circuit is coupled to the transformer circuit and the clamping energy storage circuit; when the main switch circuit is turned on, the auxiliary winding releases energy to the primary side winding. After the clamping energy storage circuit is turned on and then turned off, the main switch circuit enters zero-voltage switching. The transformer circuit obtains the conversion efficiency turning point according to the conversion efficiency ratio of the load on the transformer circuit. When the value of actual output power is less than the value of output power corresponding to the turning point of conversion efficiency, the load is light load; when the value of actual output power is greater than the value of output power corresponding to the turning point of conversion efficiency, the load is heavy load.

In one embodiment, the transformer circuit further includes a secondary winding. The secondary winding is coupled to a load. The primary side winding is coupled in parallel to the excitation inductance of the transformer circuit, and is coupled to the input voltage through the leakage inductance of the transformer circuit.

In one embodiment, the clamp tank circuit includes a switch and a diode. The switch is coupled to the input voltage and the leakage inductance. The diode is coupled to the auxiliary winding.

In one embodiment, the main switch circuit includes a main switch. One end of the main switch is coupled to the primary side winding, the magnetizing inductor and the capacitor, and the other end of the main switch is coupled to the auxiliary winding and the input voltage.

In one embodiment, when the dual-mode active clamp forward converter operates under heavy load, the switch is turned off and the main switch is turned on, the input voltage, the leakage inductance, the primary winding and the main switch form a first loop. As the current flowing through the primary winding increases, the leakage inductance stores energy and the magnetizing inductor excites, and the energy stored in the leakage inductance is transferred to the secondary winding and stores energy in the output inductor coupled to the secondary winding.

In one embodiment, when the dual-mode active clamp forward converter operates under heavy load, the switch is turned on and the main switch is turned off, the leakage inductance, the primary winding, the capacitor and the switch form the second loop. As the current of the leakage inductance flows through the capacitor and the switch, the leakage inductance releases energy, and the magnetizing inductance demagnetizes, and the energy stored in the output inductor coupled to the secondary side winding is transferred to the output capacitor to provide the required power supply for the load .

In one embodiment, when the dual-mode active clamp forward converter operates under heavy load, the switch is turned on and the main switch is turned off, the leakage inductance, the primary winding, the capacitor and the switch form a third loop. The energy stored in the output inductor coupled to the secondary side winding is transferred to the output capacitor to provide power for the load.

In one embodiment, when the dual mode active clamp forward converter is under heavy load operation, the switch is off and the main switch is off, the input voltage, the leakage inductance, the primary side winding and the back-connection parasitic on the main switch The pole body or the main switch constitutes the fourth circuit. Leakage release energy.

In one embodiment, when the dual-mode active clamp forward converter operates under light load, the switch is turned off and the main switch is turned on, the input voltage, the leakage inductance, the primary side winding and the main switch form a first loop. As the current flowing through the primary winding increases, the leakage inductance stores energy and the magnetizing inductor excites, and the energy stored in the leakage inductance is transferred to the secondary winding and stores energy in the output inductor coupled to the secondary winding.

In one embodiment, when the dual-mode active-clamp forward converter is operating at light load, the switch is turned off and the main switch is turned off, the leakage inductance, primary side winding, capacitance, and back-connected diode parasitic on the switch Or switch constitutes the second loop. As the current of the leakage inductance flows through the capacitor and the back-connected diode of the switch or the switch, the leakage inductance releases energy, and the magnetizing inductance demagnetizes, and the energy stored in the output inductor coupled to the secondary winding is transferred to the output capacitor , to provide the required power supply for the load.

In one embodiment, when the dual-mode active clamp forward converter operates under light load, the switch is turned off and the main switch is turned on, the input voltage, the diode, the auxiliary winding, the capacitor and the primary winding form a third loop , and the diode, auxiliary winding, capacitor and main switch constitute the fourth loop. In the third loop, leakage current releases energy. In the fourth loop, the capacitor is discharged to the primary side winding through the auxiliary winding.

With the proposed dual-mode active-clamp forward converter, the technical effect can be achieved: it can automatically switch the operation mode for optimal efficiency corresponding to heavy load or light load, so as to solve the technical problem that the conversion efficiency is difficult to improve, and achieve convenience operation, improving conversion efficiency, and saving power consumption costs. Furthermore, the surge ringing on the switching element can be effectively reduced, the EMI emission energy can be reduced, and the leakage inductance energy on the primary side winding can be recovered, thereby improving efficiency.

In order to further understand the technology, means and effects of this creation to achieve the intended purpose, please refer to the following detailed description and drawings about this creation. For specific understanding, however, the attached drawings are only for reference and illustration, and are not used to limit the creation.

The implementation of this creation is described below through specific specific examples, and those who are familiar with this technology can easily understand other advantages and effects of this creation from the content disclosed in this specification. This creation can also be implemented or applied through other different specific examples, and the details in this creation manual can also be modified and changed based on different viewpoints and applications without departing from the spirit of this creation.

It should be noted that the structure, proportion, size, number of components, etc. shown in the drawings attached to this manual are only used to match the content disclosed in the manual for the understanding and reading of those familiar with this technology, and are not used to limit the possibilities of this creation. The limitations of implementation, so it has no technical significance. Any modification of structure, change of proportional relationship or adjustment of size, without affecting the effect and purpose of this creation, shall fall within the scope of this article. The technical content revealed by the creation must be within the scope covered.

Hereby, the technical content and detailed description of this creation are described as follows with the drawings.

Please refer to Figure 3, which is the circuit diagram of the dual-mode active clamp forward converter created in this paper. The dual-mode active clamp forward converter described in this creation includes a transformer circuit, a clamp energy storage circuit and a main switch circuit. Wherein, the transformer circuit includes a primary winding (providing the first voltage V1), a secondary winding (providing the second voltage V2), an auxiliary winding (providing the third voltage V3), and a winding coupled between the primary winding and the auxiliary winding. Capacitor C1 (also called clamp capacitor). The clamping energy storage circuit includes a switch Q ₂ and a diode D _S2 . Further, when the load R _O is heavy, the clamping energy storage circuit is turned on and then turned off, and when the load R _O is light, the clamping energy storage circuit remains off.

The input side of the transformer circuit is coupled to the clamping energy storage circuit and the main switch circuit; the output side of the transformer circuit is coupled to a load R _O (shown as a resistance element). Under this architecture, the circuit on the primary side is coupled to the input voltage Vin. The clamping energy storage circuit is coupled to the primary winding, the auxiliary winding and the capacitor C1 of the transformer circuit.

The main switching circuit includes a main switch Q ₁ . The main switch circuit is coupled to the primary winding of the transformer circuit, the auxiliary winding, the capacitor C1 and the diode D _S2 of the clamping energy storage circuit.

When the main switch _Q1 of the main switching circuit is turned on, the auxiliary winding is discharged to the primary side winding of the transformer circuit. Wherein, after the clamping energy storage circuit is turned on and then turned off, the main switch circuit enters a zero-voltage switching (ZVS) mode.

Please refer to FIG. 4 , which is a schematic diagram of the conversion efficiency of the dual-mode active-clamp forward converter of this invention. Under the condition of inputting a constant voltage, the transformer circuit obtains a conversion efficiency turning point P _{according to the conversion efficiency ratio of the load R O to} the transformer circuit, that is, the conversion efficiency and the output power ( The unit is the relationship curve E1 of watt, watt), and the relationship curve E2 of the conversion efficiency obtained by the load R _O running in the heavy load mode and the output power. The intersection point generated by overlapping the relationship curve E1 and the relationship curve E2 is the turning point P of the conversion efficiency. When the value of the actual output power is less than the value of the output power corresponding to the turning point P of the conversion efficiency, the load R _O is defined as a light load, and the dual-mode active clamp forward converter of the present invention operates at a light load. Conversely, when the value of the actual output power is greater than the value of the output power corresponding to the turning point P of the conversion efficiency, the load R _O is defined as a heavy load, and the dual-mode active clamp forward converter of the present invention operates under heavy load. When the dual-mode active-clamp forward converter of the present invention switches between heavy load and light load, it only operates on the solid line part of the relationship curve E1 and the relationship curve E2 as shown in FIG. 4 .

Please refer to FIG. 5A to FIG. 5D , which are the first state diagram to the fourth state diagram of the dual-mode active clamp forward converter of the present invention operating under heavy load.

As shown in FIG. 5A , when the dual-mode active clamp forward converter is in the first state of heavy load, the switch _Q2 of the clamp tank circuit is turned off and the main switch _Q1 is turned on. The input voltage Vin, the leakage inductance (not shown), the primary side winding and the main switch _Q1 form a first loop. In the first loop, as the current flowing through the primary winding increases, the leakage inductance of the transformer of the transformer circuit stores energy, and the magnetizing inductor (not shown) excites. At this time, since the diode D1 coupled to the secondary winding is forward-biased, and the diode D2 is reverse-biased, the energy storage of the leakage inductance is transferred through the secondary winding coupled to the primary winding. Passed to the secondary side winding, and store energy on the output inductor L _O.

As shown in FIG. 5B , when the dual-mode active clamp forward converter is in the second state of heavy load, the switch Q ₂ of the clamp tank circuit is turned on and the main switch Q ₁ is turned off. The leakage inductance, the primary side winding, the capacitor C1 of the transformer circuit and the switch _Q2 form a second loop. In the second loop, as the current of the leakage inductance flows through the capacitor C1 and the switch Q ₂ , the leakage inductance is released and the magnetizing inductance is demagnetized. In this state, the winding voltage of the transformer is opposite, the diode D1 is turned off in the reverse bias, and the diode D2 is turned on in the forward bias, so the energy stored in the output inductor _LO is transferred to the output capacitor Co for energy storage to provide the load R _O required for power supply.

As shown in FIG. 5C , when the dual-mode active-clamp forward converter is in the third state of heavy load, the switch _Q2 of the clamp tank circuit is still turned on and the main switch _Q1 is still turned off. In this state, zero voltage soft switching (ZVS) of switch _Q2 is achieved under resonant operation of the resonant element. Therefore, when the maintenance switch _Q2 is turned on and the main switch _Q1 is turned off, the third loop formed is the same as the second state, but the current direction is opposite. In this state, the energy stored in the output inductor L _O is transferred to the output capacitor Co for energy storage to provide power for the load R _O.

As shown in FIG. 5D , when the dual-mode active clamp forward converter is in the fourth state of heavy load, the switch Q ₂ of the clamp tank circuit is turned off and the main switch Q ₁ is turned off. The input voltage Vin, the leakage inductance, the primary side winding and the back-connected diode (not shown) parasitic on the main switch Q ₁ form a fourth loop. It is worth mentioning that the main switch Q ₁ is a traditional power switch element with a back-connected diode, or a gallium nitride (GaN) switch element without a back-connected diode, which is the same below and will not be described again. In the fourth loop, leakage current releases energy. At this time, the current of the leakage inductance is negative, and the leakage inductance releases energy to the parasitic capacitance Cds parasitic on the main switch _Q1 in a series resonance manner, and the voltage of the parasitic capacitance Cds begins to drop until the current of the leakage inductance is cut off, the parasitic capacitance Cds releases energy to the leakage inductance and magnetizing inductance in the form of LC series resonance, and then the voltage of the parasitic capacitor Cds drops to zero, that is, the condition that the main switch _Q1 can perform zero-voltage soft switching (ZVS).

Please refer to FIG. 6A to FIG. 6D , which are the first state diagram to the fourth state diagram of the dual-mode active clamp forward converter of the present invention operating at light load.

As shown in FIG. 6A , when the dual-mode active-clamp forward converter operates in the first light-load state, the switch _Q2 of the clamp tank circuit is turned off and the main switch _Q1 is turned on. The input voltage Vin, the leakage inductance, the primary side winding and the main switch _Q1 form a first loop. In the first loop, as the current flowing through the primary winding increases, the leakage inductance of the transformer of the transformer circuit stores energy, and the magnetizing inductor (not shown) excites. At this time, since the diode D1 coupled to the secondary winding is forward-biased, and the diode D2 is reverse-biased, the energy storage of the leakage inductance is transferred through the secondary winding coupled to the primary winding. Passed to the secondary side winding, and store energy on the output inductor L _O.

As shown in FIG. 6B , when the dual-mode active clamp forward converter operates in the light-load second state, the switch _Q2 of the clamp tank circuit is turned off and the main switch _Q1 is turned off. The leakage inductance, the primary side winding, the capacitor C1 of the transformer circuit and the back-connected diode (not shown) parasitic on the switch _Q2 form a second loop. It is worth mentioning that the switch Q ₂ is a traditional power switch element with a back-connected diode, or a gallium nitride (GaN) switch element without a back-connected diode, which is the same below and will not be described again. In the second loop, as the current of the leakage inductance flows through the capacitor C1 and the back-connected diode of the switch _Q2 , the leakage inductance is discharged, and the magnetizing inductance is demagnetized. Since the back-connected diode of the switch _Q2 is turned on, the parasitic capacitance Cds parasitic on the switch _Q2 is discharged. At this time, if the switch _Q2 is turned on, the zero-voltage switching (ZVS) of the switch _Q2 can be realized. In this state, the winding voltage of the transformer is opposite, the diode D1 is turned off in the reverse bias, and the diode D2 is turned on in the forward bias, so the energy stored in the output inductor _LO is transferred to the output capacitor Co for energy storage to provide the load R _O required for power supply.

As shown in FIG. 6C , when the dual-mode active-clamp forward converter operates in the third light-load state, substantially the same as the light-load second state, the switch _Q2 is turned off and the main switch _Q1 is turned off. However, after the release of the leakage inductance is completed, the energy of the magnetizing inductance continues to be released to the secondary side winding.

As shown in FIG. 6D , when the dual-mode active-clamp forward converter operates in the light-load fourth state, the switch Q ₂ of the clamp tank circuit is turned off and the main switch Q ₁ is turned on. The input voltage Vin, the diode D _S2 of the clamping energy storage circuit, the auxiliary winding, the capacitor C1 and the primary side winding form a third loop. Furthermore, the diode D _S2 of the clamping energy storage circuit, the auxiliary winding, the capacitor C1 and the main switch _Q1 form a fourth loop. In the third loop, leakage current releases energy. In the fourth loop, the capacitor C1 releases energy to the primary winding through the auxiliary winding, which means that the energy of the leakage inductance temporarily stored in the capacitor C1 is transferred back to the input terminal of the transformer circuit.

When using the dual-mode active-clamp forward converter described in this invention, if the load R _O is light-loaded, the switch _Q2 of the clamp energy storage circuit is kept off, so that the light-load operates in pure energy recovery action, That is, the energy of the leakage inductance in the capacitor (clamping capacitor) C1 is released to the primary side winding of the transformer circuit through the auxiliary winding, which can reduce the switching frequency when the main switching circuit operates in valley switching (VVS) (that is, fixed frequency modulation Mode FFM mode) to obtain the best efficiency of light load operation.

If the load R _O is heavy, the clamping energy storage circuit enters the forward active clamping (ACF) mode, that is, the switch _Q2 of the clamping energy storage circuit can be turned on and then turned off, so that the main switch _Q1 of the main switching circuit operates Optimum efficiency for heavy load operation is achieved at zero voltage switching (ZVS). For this reason, the dual-mode active clamp forward converter described in this creation can automatically switch the operation mode for optimal efficiency corresponding to heavy load or light load, so as to solve the technical problem that the conversion efficiency is difficult to improve, and achieve convenient operation and improved Conversion efficiency and the purpose of saving power consumption costs. Furthermore, the surge ringing on the switching element can be effectively reduced, the EMI emission energy can be reduced, and the leakage inductance energy on the primary side winding can be recovered, thereby improving efficiency.

The above is only a detailed description and diagram of a preferred embodiment of this creation, but the characteristics of this creation are not limited to this, and are not used to limit this creation. The entire scope of this creation should be based on the scope of the following patent application As the standard, all embodiments that conform to the spirit of the patent scope of this creation and its similar changes should be included in the scope of this creation. Any person familiar with the technology can easily think of changes or changes in the field of this creation. Modifications can all be covered by the patent scope of the following case.

Vin: Input voltage Q ₁ : Main switch Q ₂ : Switch D _S2 : Diode C1: Capacitor R _O : Load E1: Relationship curve E2: Relationship curve P: Conversion efficiency turning point D1: Diode D2: Diode L _O : output inductance Co: output capacitance Cds: parasitic capacitance

Figure 1: A circuit diagram of an existing active-clamp forward converter.

Figure 2: It is a circuit diagram of an existing passive forward converter with leakage inductance energy recovery function.

Figure 3: The circuit diagram of the dual-mode active-clamp forward converter created for this paper.

Figure 4: Schematic diagram of the conversion efficiency of the dual-mode active-clamp forward converter created by the department.

FIG. 5A : The first state diagram of a dual-mode active-clamp forward converter created for the present invention operating at heavy load.

Fig. 5B: The second state diagram of the dual-mode active-clamp forward converter created for the present invention operating at heavy load.

Fig. 5C: The third state diagram of the presently authored dual-mode active-clamp forward converter operating at heavy load.

Fig. 5D: The fourth state diagram of the dual-mode active-clamp forward converter created for the present invention operating at heavy load.

Fig. 6A: The first state diagram of the dual-mode active-clamp forward converter of the present invention operating at light load.

Fig. 6B: The second state diagram of the dual-mode active-clamp forward converter created for this invention operating at light load.

Fig. 6C: The third state diagram of the dual-mode active-clamp forward converter created for this invention operating at light load.

Fig. 6D: The fourth state diagram of the dual-mode active-clamp forward converter operating at light load based on this creation.

Vin: input voltage

Q ₁ : Main switch

Q ₂ : switch

D _S2 : Diode

C1: capacitance

R _O : load

D1: Diode

D2: Diode

L _O : output inductance

Co: output capacitance

Cds: parasitic capacitance

Claims (11)

A dual-mode active-clamp forward converter consisting of: A transformer circuit, coupled to a load, and including an auxiliary winding, a capacitor and a primary side winding; A clamping energy storage circuit, coupled to the transformer circuit; wherein, when the load is heavy, the clamping energy storage circuit is turned on and then turned off; when the load is light load, the clamping energy storage circuit remains off break; and a main switch circuit, coupled to the transformer circuit and the clamping energy storage circuit; when the main switch circuit is turned on, the auxiliary winding releases energy to the primary side winding; Wherein, when the clamping energy storage circuit is turned on and then turned off, the main switch circuit enters zero-voltage switching; Wherein, the transformer circuit obtains a conversion efficiency turning point according to the conversion efficiency ratio of the load to the transformer circuit; when the value of the actual output power is less than the value of the output power corresponding to the conversion efficiency turning point, the load is light load; when the actual output When the value of the power is greater than the value of the output power corresponding to the turning point of the conversion efficiency, the load is a heavy load. For the dual-mode active-clamp forward converter described in Item 1 of the scope of the patent application, the transformer circuit further includes: A secondary winding is coupled to the load; the primary winding is coupled in parallel to a magnetizing inductance of the transformer circuit, and is coupled to an input voltage through a leakage inductance of the transformer circuit. The dual-mode active clamping forward converter described in item 2 of the scope of the patent application, wherein the clamping energy storage circuit includes: a switch coupled to the input voltage and the leakage inductance; and A diode is coupled to the auxiliary winding. The dual-mode active clamp forward converter described in item 3 of the scope of the patent application, wherein the main switch circuit includes: A main switch, one end of the main switch is coupled to the primary winding, the magnetizing inductor and the capacitor, and the other end of the main switch is coupled to the auxiliary winding and the input voltage. The dual-mode active clamp forward converter as described in item 4 of the scope of the patent application, wherein, when the dual-mode active clamp forward converter is under heavy load operation, when the switch is turned off and the main switch is turned on, The input voltage, the leakage inductance, the primary winding and the main switch form a first loop; Wherein, as the current flowing through the primary side winding increases, the leakage inductance stores energy, and the excitation inductance performs excitation, the stored energy of the leakage inductance is transferred to the secondary side winding, and is coupled to the secondary An output inductance of the side winding stores energy. The dual-mode active clamp forward converter described in item 4 of the scope of the patent application, wherein, when the dual-mode active clamp forward converter is under heavy load operation, when the switch is turned on and the main switch is turned off, The leakage inductance, the primary winding, the capacitor and the switch form a second loop; Wherein, as the current of the leakage inductance flows through the capacitor and the switch, the leakage inductance releases energy, and the magnetizing inductance demagnetizes, and the energy stored in an output inductance coupled to the secondary side winding is transmitted to a output capacitor to provide the required power supply for the load. The dual-mode active clamp forward converter described in item 4 of the scope of the patent application, wherein, when the dual-mode active clamp forward converter is under heavy load operation, when the switch is turned on and the main switch is turned off, The leakage inductance, the primary side winding, the capacitor and the switch form a third loop; Wherein, the energy stored in an output inductor coupled to the secondary side winding is transferred to an output capacitor to provide power for the load. The dual-mode active clamp forward converter as described in item 4 of the scope of the patent application, wherein, when the dual-mode active clamp forward converter is under heavy load operation, the switch is turned off and the main switch is turned off , the input voltage, the leakage inductance, the primary side winding, and a back-connected diode parasitic on the main switch or the main switch form a fourth loop; Wherein, the leakage electric release energy. The dual-mode active clamp forward converter as described in item 4 of the scope of the patent application, wherein, when the dual-mode active clamp forward converter is under light-load operation, when the switch is turned off and the main switch is turned on, The input voltage, the leakage inductance, the primary winding and the main switch form a first loop; Wherein, as the current flowing through the primary side winding increases, the leakage inductance stores energy, and the excitation inductance performs excitation, the stored energy of the leakage inductance is transferred to the secondary side winding, and is coupled to the secondary An output inductance of the side winding stores energy. The dual-mode active clamp forward converter as described in item 4 of the scope of the patent application, wherein, when the dual-mode active clamp forward converter is under light-load operation, the switch is turned off and the main switch is turned off , the leakage inductance, the primary side winding, the capacitor, and a back-connected diode parasitic on the switch or the switch constitute a second loop; Wherein, as the current of the leakage inductance flows through the capacitor and a back-connected diode of the switch or the main switch, the leakage inductance is released, and the magnetizing inductance is demagnetized, and is coupled to the secondary side winding The energy stored in an output inductor is transferred to an output capacitor to provide power for the load. The dual-mode active clamp forward converter as described in item 4 of the scope of the patent application, wherein, when the dual-mode active clamp forward converter is under light-load operation, when the switch is turned off and the main switch is turned on, The input voltage, the diode, the auxiliary winding, the capacitor and the primary winding form a third loop, and the diode, the auxiliary winding, the capacitor and the main switch form a fourth loop; Wherein, in the third loop, the leakage inductance discharges energy; in the fourth loop, the capacitor discharges energy to the primary side winding through the auxiliary winding.

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