CN219627567U - Dual mode active clamp forward converter - Google Patents

Abstract

The dual-mode active clamp forward converter comprises 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 side winding. When the load is heavy load, the clamp energy storage circuit is turned on and then turned off; when the load is light, the clamp tank circuit remains off. When the main switching circuit is turned on, the auxiliary winding releases energy to the primary side winding. After the clamp tank 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 light load. When the value of the actual output power is larger than the value of the output power corresponding to the turning point of the conversion efficiency, the load is overloaded.

Description

Dual mode active clamp forward converter

Technical Field

The present utility model relates to a dual-mode active clamp forward converter, and more particularly to a dual-mode active clamp forward converter for improving light load efficiency.

Background

Forward converters are widely used in medium to low power power conversion systems due to their simple circuit architecture, and have advantages such as electrical isolation and adjustable output voltage reduction based on turn ratio. However, due to the presence of transformer leakage inductance, when the switch conducts the primary side magnetized inductance for energy storage, the leakage inductance will also store energy accordingly. When the switch cuts off the magnetization inductance and begins to release energy on the secondary side, if there is no released path for the energy of the leakage inductance, it will release energy on the capacitance Cd (i.e. the parasitic capacitance between the drain source) of the power switch, causing a sharp increase in the voltage Vds between the drain source, resulting in a correspondingly high surge voltage and causing damage to the power switch. In recent years, in order to improve the above problems, active clamping technology has been proposed one after another.

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

The efficiency characteristics of the two frameworks are as follows: the active clamp forward converter of fig. 1 operates at low input voltage and heavy load conditions with higher conversion efficiency, but operates at high input voltage and light load with significantly lower conversion efficiency than the passive forward converter of fig. 2.

Therefore, how to design a dual-mode active clamp forward converter, especially one that can automatically switch the operation mode with optimized efficiency corresponding to heavy load or light load, solves the problems and technical bottlenecks existing in the prior art, and is an important issue studied by the present inventor.

Disclosure of Invention

To solve the above problem, a dual mode active clamp forward converter includes: a transformer circuit coupled to the load and including an auxiliary winding, a capacitor, and a primary side winding;

a clamp tank circuit 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 load, the clamp energy storage circuit is kept off; and

a main switch circuit coupled to the transformer circuit and the clamp tank circuit; when the main switch circuit is turned on, the auxiliary winding releases energy to the primary side winding;

after the clamp energy storage circuit is turned on and turned off, the main switch circuit enters zero-voltage switching;

the transformer circuit obtains a conversion efficiency turning point according to the conversion efficiency proportion of the load on the transformer circuit; 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 larger than the value of the output power corresponding to the turning point of the conversion efficiency, the load is overloaded.

Further, the transformer circuit further includes: a secondary side winding coupled to the load; the primary winding is coupled in parallel with the excitation inductance of the transformer circuit and coupled to the input voltage through the leakage inductance of the transformer circuit.

Further, the clamp tank circuit includes: a switch coupled to the input voltage and the leakage inductance; and a diode coupled to the auxiliary winding.

Further, the main switching circuit includes: one end of the main switch is coupled with the primary side winding, the exciting inductor and the capacitor, and the other end of the main switch is coupled with the auxiliary winding and the input voltage.

Further, when the switch is turned off and the main switch is turned on under heavy load operation of the dual-mode active clamp forward converter, the input voltage, the leakage inductance, the primary winding and the main switch form a first loop;

the leakage inductance stores energy as the current flowing through the primary side winding increases, and the excitation inductance excites, and the energy stored by the leakage inductance is transferred to the secondary side winding and stores energy for an output inductance coupled to the secondary side winding.

Further, when the switch is turned on and the main switch is turned off under heavy load operation of the dual-mode active clamp forward converter, the leakage inductance, the primary winding, the capacitor and the switch form a second loop;

the leakage inductance releases energy and the excitation inductance demagnetizes along with the current of the leakage inductance flowing through the capacitor and the switch, and the energy stored in an output inductance coupled to the secondary side winding is transmitted to the output capacitor to supply power to the load.

Further, when the switch is turned on and the main switch is turned off under heavy load operation of the dual-mode active clamp forward converter, the leakage inductance, the primary winding, the capacitor and the switch form a third loop;

wherein, the energy stored in an output inductor coupled to the secondary winding is transferred to the output capacitor to provide the power supply for the load.

Further, when the switch is turned off and the main switch is turned off in the heavy load operation of the dual-mode active clamp forward converter, the input voltage, the leakage inductance, the primary winding, and a back diode parasitic to the main switch or the main switch form a fourth loop;

wherein the leakage inductance releases energy.

Further, when the switch is turned off and the main switch is turned on under a light load operation of the dual-mode active clamp forward converter, the input voltage, the leakage inductance, the primary side winding and the main switch form a first loop;

the leakage inductance stores energy as the current flowing through the primary side winding increases, and the excitation inductance excites, and the energy stored by the leakage inductance is transferred to the secondary side winding and stores energy for an output inductance coupled to the secondary side winding.

Further, when the switch is turned off and the main switch is turned off in the light load operation of the dual-mode active clamp forward converter, the leakage inductance, the primary winding, the capacitor and the back diode parasitic to the switch or the switch form a second loop;

the leakage inductance releases energy and the excitation inductance demagnetizes along with the current of the leakage inductance flowing through the capacitor and the back diode or the main switch of the switch, and the energy stored by the output inductance coupled with the secondary side winding is transmitted to the output capacitor to supply power to the load.

Further, when the switch is turned off and the main switch is turned on in the light load operation of the dual-mode active clamp forward converter, 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 releases energy; in the fourth loop, the capacitor releases energy through the auxiliary winding to the primary winding.

The beneficial effects of this novel are: the dual mode active clamp forward converter includes a transformer circuit, a clamp tank circuit, and a main switch circuit. The transformer circuit is coupled to the load and includes an auxiliary winding, a capacitor, and a primary winding. The clamping energy storage circuit is coupled with the transformer circuit. When the load is heavy load, the clamp energy storage circuit is turned on and then turned off; when the load is light, the clamp tank circuit remains off. The main switch circuit is coupled with the transformer circuit and the clamping energy storage circuit; when the main switching circuit is turned on, the auxiliary winding releases energy to the primary side winding. After the clamp tank circuit is turned on and then turned off, the main switch circuit enters zero-voltage switching. The transformer circuit obtains a conversion efficiency turning point according to the conversion efficiency proportion of the load on the transformer circuit. 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 larger than the value of the output power corresponding to the turning point of the conversion efficiency, the load is overloaded.

Drawings

Fig. 1 is a circuit diagram of a conventional active clamp forward converter.

FIG. 2 is a circuit diagram of a conventional passive forward converter with leakage inductance energy recovery.

FIG. 3 is a circuit diagram of a dual mode active clamp forward converter according to the present utility model.

FIG. 4 is a schematic diagram illustrating the conversion efficiency of the dual-mode active clamp forward converter according to the present utility model.

FIG. 5A is a first state diagram of the dual mode active clamp forward converter of the present utility model operating in heavy load.

FIG. 5B is a second state diagram of the dual mode active clamp forward converter of the present utility model operating in heavy load.

FIG. 5C is a third state diagram illustrating the operation of the dual mode active clamp forward converter in heavy load according to the present utility model.

FIG. 5D is a fourth state diagram of the application of the dual mode active clamp forward converter operating under heavy load.

FIG. 6A is a first state diagram of the dual-mode active clamp forward converter of the present utility model operating under light load.

FIG. 6B is a second state diagram of the dual mode active clamp forward converter of the present utility model operating under light load.

FIG. 6C is a third state diagram of the dual mode active clamp forward converter of the present utility model operating under light load.

FIG. 6D is a fourth state diagram of the dual mode active clamp forward converter of the present utility model operating under light load.

Wherein: vin is input voltage, Q1 is main switch, Q2 is switch, DS2 is diode, C1 is capacitor, RO is load, E1 is relation curve, E2 is relation curve, P is conversion efficiency turning point, D1 is diode, D2 is diode, LO is output inductance, co is output capacitance, cds is parasitic capacitance.

Detailed Description

The technical content and detailed description of the present utility model are as follows in conjunction with the drawings:

referring to fig. 3, the dual-mode active clamp forward converter includes a transformer circuit, a clamp energy storage circuit, and a main switch circuit. The transformer circuit includes a primary winding (providing a first voltage V1), a secondary winding (providing a second voltage V2), an auxiliary winding (providing a third voltage V3), and a capacitor C1 (which may also be referred to as a clamp capacitor) coupled between the primary winding and the auxiliary winding. The clamp tank circuit includes a switch Q2 and a diode DS2. Further, when the load RO is heavy load, the clamp tank circuit is turned on and turned off, and when the load RO is light load, the clamp tank circuit is kept turned off.

The input side of the transformer circuit is coupled with the clamping energy storage circuit and the main switch circuit; the output side of the transformer circuit is coupled to a load RO (illustrated as a resistive element). Under this architecture, the primary side circuit is coupled to the input voltage Vin. The clamp energy storage circuit is coupled to the primary winding, the auxiliary winding and the capacitor C1 of the transformer circuit.

The main switch circuit includes a main switch Q1. The main switching circuit is coupled to the primary winding, the auxiliary winding, and the capacitor C1 of the transformer circuit and the diode DS2 of the clamp tank circuit.

When the main switch Q1 of the main switch circuit is turned on, the auxiliary winding releases energy to the primary side winding of the transformer circuit. Wherein the main switching circuit enters a zero-voltage switching (ZVS) mode after the clamp tank is turned on and then turned off.

Please refer to fig. 4, which is a schematic diagram illustrating a conversion efficiency of the dual-mode active clamp forward converter. Under the condition of inputting a fixed voltage, the transformer circuit obtains a conversion efficiency turning point P according to the conversion efficiency proportion of the load RO in the transformer circuit, namely a relation curve E1 of the conversion efficiency obtained by the load RO operating in a light load mode and output power (watt unit), and a relation curve E2 of the conversion efficiency obtained by the load RO operating in a heavy load mode. The crossover point generated by overlapping the relationship curve E1 and the relationship curve E2 is the conversion efficiency turning point P. When the value of the actual output power is smaller than the value of the output power corresponding to the conversion efficiency turning point P, the load RO is defined as a light load, and the dual-mode active clamping forward converter operates in the light load. Otherwise, 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 RO is defined as the reload, and the dual-mode active clamp forward converter operates under the reload. The dual-mode active clamp forward converter of the present utility model is only operated on the solid line portion of the relationship curve E1 and the relationship curve E2 shown in FIG. 4 when switching heavy load or light load.

Please refer to fig. 5A-5D, which illustrate a dual-mode active clamp forward converter operating in a first state diagram to a fourth state diagram of 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 is turned off and the main switch Q1 is turned on. The input voltage Vin, leakage inductance (not shown), primary side winding, and main switch Q1 constitute a first loop. In the first loop, as the current flowing through the primary winding increases, the leakage inductance of the transformer circuit stores energy, and the excitation inductance (not shown) excites. At this time, since the diode D1 coupled to the secondary winding is turned on in forward bias and the diode D2 is turned off in reverse bias, the stored energy of the leakage inductance is transferred to the secondary winding through the secondary winding coupled to the primary winding, and the output inductance LO is stored.

As shown in fig. 5B, when the dual-mode active clamp forward converter is in the second state with heavy load, the switch Q2 of the clamp tank is turned on and the main switch Q1 is turned off. The leakage inductance, the primary winding, the capacitance C1 of the transformer circuit and the switch Q2 constitute a second loop. In the second loop, as the current of the leakage inductance flows through the capacitor C1 and the switch Q2, the leakage inductance releases energy, and the excitation inductance demagnetizes. In this state, the winding voltage of the transformer is opposite, the diode D1 is turned off in reverse bias, and the diode D2 is turned on in forward bias, so that the energy stored in the output inductor LO is transferred to the output capacitor Co to store energy, so as to supply the load RO.

As shown in fig. 5C, the switch Q2 of the clamp tank is still turned on and the main switch Q1 is still turned off when the dual-mode active clamp forward converter is in the third heavy-duty state. In this state, zero voltage soft switching (ZVS) of the switch Q2 is achieved under the resonance operation of the resonance element. Therefore, the third loop is configured in the same manner as the second state with the maintenance switch Q2 turned on and the main switch Q1 turned off, but the current direction is opposite. In this state, the energy stored in the output inductor LO is transferred to the output capacitor Co to store energy, so as to provide the power for the load RO.

As shown in fig. 5D, the switch Q2 of the clamp tank is turned off and the main switch Q1 is turned off when the dual-mode active clamp forward converter is in the heavy-duty fourth state. The input voltage Vin, the leakage inductance, the primary winding and a back-connected diode (not shown) parasitic to the main switch Q1 form a fourth loop. It should be noted that the main switch Q1 is a conventional power switch device with a back diode, or may be a gallium nitride (GaN) switch device without a back diode, and the same will not be repeated. In the fourth loop, the leakage inductance releases energy. At this time, the current of the leakage inductance is negative, the leakage inductance releases energy to the parasitic capacitance Cds parasitic to the main switch Q1 in a series resonance mode, and the voltage of the parasitic capacitance Cds begins to decrease until the current of the leakage inductance is cut off, the parasitic capacitance Cds releases energy to the leakage inductance and the excitation inductance in an LC series resonance mode, and then the voltage of the parasitic capacitance Cds decreases to zero, so as to achieve the condition that the main switch Q1 can perform zero voltage soft switching (ZVS).

Referring to fig. 6A to 6D, the dual-mode active clamp forward converter of the present utility model is operated in a first state diagram to a fourth state diagram under light load.

As shown in fig. 6A, when the dual-mode active clamp forward converter is operated in the first state of light load, the switch Q2 of the clamp tank circuit is turned off and the main switch Q1 is turned on. The input voltage Vin, leakage inductance, primary side winding and main switch Q1 constitute a first loop. In the first loop, as the current flowing through the primary winding increases, the leakage inductance of the transformer circuit stores energy, and the excitation inductance (not shown) excites. At this time, since the diode D1 coupled to the secondary winding is turned on in forward bias and the diode D2 is turned off in reverse bias, the stored energy of the leakage inductance is transferred to the secondary winding through the secondary winding coupled to the primary winding, and the output inductance LO is stored.

As shown in fig. 6B, when the dual-mode active clamp forward converter is operated in the second state of light load, the switch Q2 of the clamp tank circuit is turned off and the main switch Q1 is turned off. The leakage inductance, the primary winding, the capacitor C1 of the transformer circuit and a back diode (not shown) parasitic to the switch Q2 form a second loop. It should be noted that the switch Q2 is a conventional power switch device with a back-connected diode, or may be a gallium nitride (GaN) switch device without a back-connected diode, and the same will not be repeated. In the second loop, as the current of the leakage inductance flows through the capacitor C1 and the back diode of the switch Q2, the leakage inductance releases energy, and the excitation inductance demagnetizes. Since the back diode of the switch Q2 is turned on, the parasitic capacitance Cds parasitic to the switch Q2 discharges. At this time, when the switch Q2 is turned on, zero Voltage Switching (ZVS) of the switch Q2 can be achieved. In this state, the winding voltage of the transformer is opposite, the diode D1 is turned off in reverse bias, and the diode D2 is turned on in forward bias, so that the energy stored in the output inductor LO is transferred to the output capacitor Co to store energy, so as to supply the load RO.

As shown in fig. 6C, when the dual-mode active clamp forward converter is operated in the third state of light load, the switch Q2 is turned off and the main switch Q1 is turned off, which is substantially the same as the second state of light load. However, after the energy release of the leakage inductance is completed, the energy of the excitation inductance is continuously released to the secondary side winding.

As shown in fig. 6D, when the dual-mode active clamp forward converter is operating in the fourth state of light load, the switch Q2 of the clamp tank is turned off and the main switch Q1 is turned on. The input voltage Vin, the diode DS2 of the clamp tank, the auxiliary winding, the capacitor C1 and the primary winding form a third loop. Further, the diode DS2, the auxiliary winding, the capacitor C1 and the main switch Q1 of the clamp tank circuit constitute a fourth loop. In the third loop, the leakage inductance releases energy. In the fourth circuit, the capacitor C1 releases energy to the primary winding through the auxiliary winding, i.e. the energy of the leakage inductance temporarily stored in the capacitor C1 is transferred back to the input of the transformer circuit.

When the dual-mode active clamp forward converter is used, if the load RO is a light load, the switch Q2 of the clamp energy storage circuit is kept off, so that the light load operates in a simple energy recovery action, namely, the energy of leakage inductance in the capacitor (clamp capacitor) C1 is released to the primary side winding of the transformer circuit through the auxiliary winding, and the switching frequency (namely, the fixed frequency modulation mode FFM mode) when the main switching circuit operates in a valley switching (VVS) can be reduced, so that the optimal efficiency of the light load operation is obtained.

If the load RO is heavy load, the clamp tank circuit enters a forward Active Clamp (ACF) mode, i.e., the switch Q2 of the clamp tank circuit is turned on and then turned off, so that the main switch Q1 of the main switch circuit operates at Zero Voltage Switching (ZVS) to obtain the optimal efficiency of heavy load operation. Therefore, the dual-mode active clamp forward converter can automatically switch the operation mode with optimized efficiency corresponding to heavy load or light load, so as to solve the technical problem that the conversion efficiency is difficult to be improved, and achieve the purposes of convenient operation, improvement of the conversion efficiency and saving of power consumption cost. 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 the efficiency.

The foregoing detailed description and drawings of the preferred embodiments of the present utility model are provided for illustration only, and not for the purpose of limiting the utility model as defined by the appended claims, as long as they are intended to cover all such modifications and variations as fall within the true spirit and scope of the present utility model.

Claims (11)

1. A dual mode active clamp forward converter comprising: a transformer circuit coupled to the load and including an auxiliary winding, a capacitor, and a primary side winding;

a clamp tank circuit 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 load, the clamp energy storage circuit is kept off; and

a main switch circuit coupled to the transformer circuit and the clamp tank circuit; when the main switch circuit is turned on, the auxiliary winding releases energy to the primary side winding;

after the clamp energy storage circuit is turned on and turned off, the main switch circuit enters zero-voltage switching;

the transformer circuit obtains a conversion efficiency turning point according to the conversion efficiency proportion of the load on the transformer circuit; 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 larger than the value of the output power corresponding to the turning point of the conversion efficiency, the load is overloaded.

2. The dual mode active clamp forward converter of claim 1 wherein: the transformer circuit further includes:

a secondary side winding coupled to the load; the primary winding is coupled in parallel with the excitation inductance of the transformer circuit and coupled to the input voltage through the leakage inductance of the transformer circuit.

3. The dual mode active clamp forward converter of claim 2 wherein: the clamp tank circuit includes: a switch coupled to the input voltage and the leakage inductance; and a diode coupled to the auxiliary winding.

4. A dual mode active clamp forward converter as claimed in claim 3 wherein: the main switching circuit includes: one end of the main switch is coupled with the primary side winding, the exciting inductor and the capacitor, and the other end of the main switch is coupled with the auxiliary winding and the input voltage.

5. The dual mode active clamp forward converter of claim 4 wherein: when the switch is turned off and the main switch is turned on under heavy load operation of the dual-mode active clamp forward converter, the input voltage, the leakage inductance, the primary side winding and the main switch form a first loop;

the leakage inductance stores energy as the current flowing through the primary side winding increases, and the excitation inductance excites, and the energy stored by the leakage inductance is transferred to the secondary side winding and stores energy for an output inductance coupled to the secondary side winding.

6. The dual mode active clamp forward converter of claim 4 wherein: when the switch is turned on and the main switch is turned off under heavy load operation of the dual-mode active clamp forward converter, the leakage inductance, the primary side winding, the capacitor and the switch form a second loop;

the leakage inductance releases energy and the excitation inductance demagnetizes along with the current of the leakage inductance flowing through the capacitor and the switch, and the energy stored in an output inductance coupled to the secondary side winding is transmitted to the output capacitor to supply power to the load.

7. The dual mode active clamp forward converter of claim 4 wherein: when the switch is turned on and the main switch is turned off under heavy load operation of the dual-mode active clamp forward converter, 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 winding is transferred to the output capacitor to provide the power supply for the load.

8. The dual mode active clamp forward converter of claim 4 wherein: when the switch is turned off and the main switch is turned off under the heavy load operation of the dual-mode active clamp forward converter, the input voltage, the leakage inductance, the primary side winding and a back diode parasitic to the main switch or the main switch form a fourth loop;

wherein the leakage inductance releases energy.

9. The dual mode active clamp forward converter of claim 4 wherein: when the switch is turned off and the main switch is turned on under the light load operation of the dual-mode active clamp forward converter, the input voltage, the leakage inductance, the primary side winding and the main switch form a first loop;

the leakage inductance stores energy as the current flowing through the primary side winding increases, and the excitation inductance excites, and the energy stored by the leakage inductance is transferred to the secondary side winding and stores energy for an output inductance coupled to the secondary side winding.

10. The dual mode active clamp forward converter of claim 4 wherein: when the switch is turned off and the main switch is turned off under light load operation of the dual-mode active clamp forward converter, the leakage inductance, the primary side winding, the capacitor and a back diode parasitic to the switch or the switch form a second loop;

the leakage inductance releases energy and the excitation inductance demagnetizes along with the current of the leakage inductance flowing through the capacitor and the back diode or the main switch of the switch, and the energy stored by the output inductance coupled with the secondary side winding is transmitted to the output capacitor to supply power to the load.

11. The dual mode active clamp forward converter of claim 4 wherein: when the switch is turned off and the main switch is turned on in light load operation of the dual-mode active clamp forward converter, the input voltage, the diode, the auxiliary winding, the capacitor and the primary side 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 releases energy; in the fourth loop, the capacitor releases energy through the auxiliary winding to the primary winding.