Resonant state controllable active clamp flyback circuit and device thereof

Abstract

The application provides a resonant state controllable active clamp flyback circuit and a device thereof, which comprises a voltage source, a clamp capacitor, a clamp switch tube loop, a main switch tube loop, a primary winding loop, a secondary winding loop, a secondary rectification switch tube loop, a controllable capacitor switching loop and an LC filter; the voltage source is connected with the clamp capacitor and the primary winding loop; the clamp capacitor is connected with the clamp switch tube loop; the clamp switch tube loop is connected with the primary winding and the main switch tube loop; the secondary rectification switch tube loop is connected in series on the secondary winding loop; and the controllable capacitor switching loop and the LC filter are connected in parallel on the secondary winding loop. In the existing active clamp flyback circuit, soft switching cannot be ensured in the case of large input and output changes, and the voltage stress of the primary main switch tube cannot be considered. According to the scheme, the resonant state can be dynamically adjusted according to the input and output changes, the soft switching can be ensured, and the voltage stress of the primary main switch tube is reduced.

Description

Technical Field

[0001] This invention relates to the field of active clamp flyback converter technology, specifically to an active clamp flyback circuit and device with controllable resonant state. Background Technology

[0002] Active clamp flyback converters are widely used in mobile phone fast charging, computer adapters, and other fields. Active clamp flyback converters can fully utilize the leakage inductance energy of the transformer to achieve soft switching, which helps reduce power loss and increase power density. Currently, commercially available active clamp flyback converters can be divided into two types based on their resonant mode: primary-side resonant and secondary-side resonant. Figure 1 As shown, when C o / n 2 >>C C When it is primary-side resonance, when C o / n 2 < <C C This is a secondary-side resonant circuit. Primary-side resonant circuits have simple parameter design and small effective secondary current, but they suffer from the problem of accidental turn-off of the secondary rectifier diodes. Secondary-side resonant circuits can avoid accidental turn-off, but they produce large output ripple, requiring the addition of an LC filter.

[0003] Existing technologies typically achieve soft switching by dynamically adjusting the dead time of the main switch and clamping switch based on the input voltage and load current. Figure 2 As shown. However, this method still cannot ensure soft switching when the input or output changes significantly, and it cannot adjust the voltage stress on the primary-side main switch when the output load increases. Therefore, it is not applicable in situations with large input-output variations.

[0004] Patent CN 114070090 A proposes a series-type active-clamp flyback converter, such as... Figure 3 As shown, the flyback converter has a capacitor C connected in series with the primary winding. c1 This can reduce the voltage stress on the main switch Q1 to some extent, but compared to traditional active clamp flyback converters, it affects the energy storage process of the magnetizing inductor, leading to control difficulties. Patent CN 111262444 A proposes a control method for the synchronous rectifier diode under active clamp flyback secondary-side resonance conditions, such as... Figure 4 As shown, although this method achieves ZCS turn-off of the secondary rectifier diode, it cannot adjust the voltage stress of the primary main switch.

[0005] Generally, the active clamp flyback converter in the prior art has fixed resonant parameters when the input and output switching frequency parameters are determined, so that the converter can only work in a fixed resonant state. Due to the fixed resonant state, soft switching can only be realized by adjusting the turn-on and turn-off time of the clamp switch tube and the main switch, but in order to ensure the stability of the system, the switching frequency can only be changed within a certain range, and in fact the adjustable range is not high. In the case of large input and output changes, it is impossible to ensure the realization of soft switching; at the same time, due to the fixed resonant mode, the efficiency of the converter and the voltage stress of the primary main switch cannot be balanced and adjusted.

[0006] In view of this, the present application is proposed. SUMMARY

[0007] The purpose of the present application is to provide a resonant state controllable active clamp flyback circuit and its device, which can effectively solve the problems of the active clamp flyback circuit in the prior art, such as low adjustable range, inability to ensure the realization of soft switching in the case of large input and output changes, and inability to balance and adjust the voltage stress of the primary main switch.

[0008] The present application provides a resonant state controllable active clamp flyback circuit, characterized in that it comprises a voltage source, a clamp capacitor, a clamp switch tube circuit, a main switch tube circuit, a primary winding circuit, a secondary winding circuit, a secondary rectifier switch tube circuit, a controllable capacitor switching circuit and an LC filter.

[0009] The positive electrode of the voltage source is electrically connected to one end of the clamp capacitor and the first end of the primary winding circuit, the other end of the clamp capacitor is electrically connected to the first end of the clamp switch tube circuit, the second end of the clamp switch tube circuit is electrically connected to the second end of the primary winding circuit and the first end of the main switch tube circuit, the second end of the main switch tube circuit is grounded, the secondary rectifier switch tube circuit is connected in series on the secondary winding circuit, the controllable capacitor switching circuit and the LC filter are connected in parallel on the secondary winding circuit, and the LC filter is used to be connected with a load.

[0010] The control end of the clamp switch tube circuit, the control end of the main switch tube circuit, the control end of the secondary rectifier switch tube circuit and the control end of the controllable capacitor switching circuit are electrically connected to the output end of the controller.

[0011] Preferably, the clamping switch tube circuit comprises a clamping switch tube, and a clamping switch parasitic capacitor, the other end of the clamping capacitor is electrically connected with the drain of the clamping switch tube, one end of the clamping switch parasitic capacitor, the source of the clamping switch tube, the other end of the clamping switch parasitic capacitor is electrically connected with the second end of the primary winding circuit, and the gate of the clamping switch tube is electrically connected with the output end of the controller.

[0012] Preferably, the main switch tube circuit comprises a main switch tube, and a main switch parasitic capacitor, the drain of the main switch tube, one end of the main switch parasitic capacitor is electrically connected with the second end of the primary winding circuit, the source of the main switch tube, the other end of the main switch parasitic capacitor is grounded, and the gate of the main switch tube is electrically connected with the output end of the controller.

[0013] Preferably, the primary winding circuit comprises an excitation inductor, a leakage inductor, and a primary winding of a transformer, one end of the leakage inductor is electrically connected with the positive electrode of the voltage source, the other end of the leakage inductor is electrically connected with one end of the excitation inductor and the same end of the primary winding, the other end of the excitation inductor and the different end of the primary winding are electrically connected with the second end of the clamping switch tube circuit.

[0014] Preferably, the secondary winding circuit comprises a secondary winding of a transformer, a secondary resonance capacitor, the first end of the secondary resonance capacitor, the first end of the controllable capacitor switching circuit, and the first end of the LC filter are electrically connected with the different end of the secondary winding, the same end of the secondary winding is electrically connected with the first end of the secondary rectification switch tube circuit, the second end of the secondary rectification switch tube circuit, the two ends of the secondary resonance capacitor, the second end of the controllable capacitor switching circuit, and the second end of the LC filter are electrically connected with the second end of the secondary winding.

[0015] Preferably, the secondary rectification switch tube circuit comprises a secondary rectification switch tube, and a secondary rectification switch parasitic capacitor, the same end of the secondary winding is electrically connected with the drain of the secondary rectification switch tube and one end of the secondary rectification switch parasitic capacitor, the source of the secondary rectification switch tube, the other end of the secondary rectification switch parasitic capacitor is electrically connected with one end of the secondary resonance capacitor, and the gate of the secondary rectification switch tube is electrically connected with the output end of the controller.

[0016] Preferably, the controllable capacitor switching circuit comprises a controllable switch tube, and a switchable capacitor, one end of the secondary resonance capacitor is electrically connected with the source of the controllable switch tube, the drain of the controllable switch tube is electrically connected with one end of the switchable capacitor, the other end of the switchable capacitor is electrically connected with the other end of the secondary resonance capacitor, and the gate of the controllable switch tube is electrically connected with the output end of the controller.

[0017] Preferably, the LC filter comprises an output inductor, and an output capacitor, one end of the auxiliary side resonant capacitor is electrically connected with one end of the output inductor, the other end of the output inductor is electrically connected with one end of the output capacitor, the other end of the output capacitor is electrically connected with the other end of the auxiliary side resonant capacitor, and the output capacitor is used in parallel connection with a load.

[0018] The application also provides a resonant state controllable active clamp flyback device, comprising a controller and the resonant state controllable active clamp flyback circuit according to any one of the above, and the output end of the controller is electrically connected with the control end of the clamp switch tube loop, the main switch tube loop, the auxiliary side rectifier switch tube loop and the controllable capacitor switching loop.

[0019] The controllable capacitor switching loop can be composed of one or more same loops in parallel connection, thereby providing one or more resonant states, so that the adjustment of the resonant state is more flexible.

[0020] In summary, the resonant state controllable active clamp flyback circuit and the device thereof provided by the embodiment change the resonant state and the parameter, judge whether to turn on the controllable capacitor switching loop according to the change of the input and output voltage and current, change the resonant state and the resonant mode of the converter, ensure the soft switching of the circuit in the case of wide range of input and output voltage and current, and reduce the voltage stress of the primary side main switch. Thus, the problems in the prior art that the adjustable range is not high, the soft switching cannot be ensured in the case of large output change, and the voltage stress of the primary side main switch cannot be balanced and adjusted are solved. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 FIG. 1 is a circuit schematic diagram of an active clamp flyback converter in the prior art.

[0022] Figure 2 FIG. 2 is a schematic diagram of an active clamp flyback converter with dynamically adjusted dead time in the prior art.

[0023] Figure 3 FIG. 3 is a schematic diagram of a series active clamp flyback converter in the prior art.

[0024] Figure 4 FIG. 4 is a schematic diagram of a synchronous rectifier control method in the case of auxiliary side resonance of an active clamp flyback converter in the prior art.

[0025] Figure 5 FIG. 5 is a circuit schematic diagram of the resonant state controllable active clamp flyback circuit provided by the embodiment of the application.

[0026] Figure 6 is the circuit schematic diagram of the controllable switched capacitor circuit of the present application when Sa is turned on.

[0027] Figure 7 is the circuit schematic diagram of the controllable switched capacitor circuit of the present application when Sa is turned off. DETAILED DESCRIPTION

[0028] In order to make the objects, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the scope of the present application. Therefore, the following detailed description of the embodiments of the present application provided in the drawings is not intended to limit the scope of the claimed present application, but only represents selected embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the scope of the present application.

[0029] The specific embodiments of the present application are described in detail below with reference to the accompanying drawings.

[0030] Please refer to Figure 5 The first embodiment of the present application provides a resonant state controllable active clamp flyback circuit, comprising a voltage source Vin, a clamp capacitor Cc, a clamp switch tube circuit, a main switch tube circuit, a primary winding circuit, a secondary winding circuit, a secondary rectifier switch tube circuit, a controllable capacitor switching circuit and an LC filter.

[0031] The positive electrode of the voltage source Vin is electrically connected with one end of the clamp capacitor Cc and the first end of the primary winding circuit, the other end of the clamp capacitor Cc is electrically connected with the first end of the clamp switch tube circuit, the second end of the clamp switch tube circuit is electrically connected with the second end of the primary winding circuit and the first end of the main switch tube circuit, the second end of the main switch tube circuit is grounded, the secondary rectifier switch tube circuit is connected in series on the secondary winding circuit, the controllable capacitor switching circuit and the LC filter are connected in parallel on the secondary winding circuit, and the LC filter is used to be connected with a load.

[0032] The control end of the clamp switch tube circuit, the control end of the main switch tube circuit, the control end of the secondary rectifier switch tube circuit and the control end of the controllable capacitor switching circuit are used to be electrically connected with the output end of a controller.

[0033] Specifically, in the embodiment, the resonant state controllable active clamp flyback circuit changes the resonant parameters and the resonant state, adds one or more controllable capacitor switching circuits in the secondary side, judges whether to turn on the controllable capacitor switching circuit according to the size of the input voltage output load current, that is, the input and output conditions of the system, dynamically adjusts the resonant state and the resonant mode of the active clamp flyback converter, changes the resonant state and the resonant mode of the converter, ensures the soft switching of the circuit in the wide input and output change range, reduces the voltage stress of the primary side main switch, and reduces the output voltage ripple and other purposes.

[0034] In a possible embodiment of the present application, the clamping switch tube circuit comprises a clamping switch tube SH and a clamping switch parasitic capacitor CH, the other end of the clamping capacitor Cc is electrically connected with the drain of the clamping switch tube SH and one end of the clamping switch parasitic capacitor CH, the source of the clamping switch tube SH and the other end of the clamping switch parasitic capacitor CH are electrically connected with the second end of the primary winding circuit, and the gate of the clamping switch tube SH is electrically connected with the output end of the controller. The main switch tube circuit comprises a main switch tube SL and a main switch parasitic capacitor CL, the drain of the main switch tube SL and one end of the main switch parasitic capacitor CL are electrically connected with the second end of the primary winding circuit, the source of the main switch tube SL and the other end of the main switch parasitic capacitor CL are grounded, and the gate of the main switch tube SL is electrically connected with the output end of the controller. The primary winding circuit comprises an excitation inductor Lm, a leakage inductor Lk and a primary winding of a winding transformer, one end of the leakage inductor Lk is electrically connected with the positive electrode of the voltage source Vin, the other end of the leakage inductor Lk is electrically connected with one end of the excitation inductor Lm and the same end of the primary winding, and the other end of the excitation inductor Lm and the different end of the primary winding are electrically connected with the second end of the clamping switch tube circuit. The secondary winding circuit comprises a secondary winding of a transformer and a secondary resonant capacitor Cf1, the first end of the secondary resonant capacitor Cf1, the first end of the controllable capacitor switching circuit and the first end of the LC filter are electrically connected with the different end of the secondary winding. The same end of the secondary winding is electrically connected with the first end of the secondary rectification switch tube circuit, the second end of the secondary rectification switch tube circuit, the second end of the secondary resonant capacitor Cf1, the second end of the controllable capacitor switching circuit and the second end of the LC filter are electrically connected with the second end of the secondary winding. The secondary rectification switch tube circuit comprises a secondary rectification switch tube SD and a secondary rectification switch parasitic capacitor CD, the same end of the secondary winding is electrically connected with the drain of the secondary rectification switch tube SD and one end of the secondary rectification switch parasitic capacitor CD, the source of the secondary rectification switch tube SD and the other end of the secondary rectification switch parasitic capacitor CD are electrically connected with one end of the secondary resonant capacitor Cf1, and the gate of the secondary rectification switch tube SD is electrically connected with the output end of the controller. The controllable capacitor switching circuit comprises a controllable switch tube Sa and a switchable capacitor Ca, one end of the secondary resonant capacitor Cf1 is electrically connected with the source of the controllable switch tube Sa, the drain of the controllable switch tube Sa is electrically connected with one end of the switchable capacitor Ca, the other end of the switchable capacitor Ca is electrically connected with the other end of the secondary resonant capacitor Cf1, and the gate of the controllable switch tube is electrically connected with the output end of the controller.The LC filter comprises an output inductor Lf1 and an output capacitor Cf2, one end of the output inductor Lf1 is electrically connected to one end of the secondary side resonant capacitor Cf1, the other end of the output inductor Lf1 is electrically connected to one end of the output capacitor Cf2, and the other end of the output capacitor Cf2 is electrically connected to the other end of the secondary side resonant capacitor Cf1, and the output capacitor Cf2 is used in parallel with the load.

[0035] Specifically, in the present embodiment, the output inductor Lf1 and the output capacitor Cf2 constitute the LC filter, the output inductor Lf1 can decouple the output capacitor Cf2 from the primary side capacitor inductance, and reduce the ripple of the output voltage. Wherein, the ratio of the primary side winding to the secondary side winding is n:1, and Cf1 / n2 << Cc. It should be noted that the controllable capacitor loop composed of the switchable capacitor Ca and the controllable switch Sa can be more than one. The resonant state controllable active clamp flyback circuit controls the on-off of the controllable switch Sa according to the input and output changes, and determines whether the switchable capacitor Ca is connected to the circuit, thereby changing the resonant state and resonant mode of the converter, ensuring soft switching of the circuit in a wide input and output change range, and reducing the voltage stress of the primary side main switch.

[0036] In the present embodiment, when the output load current is small, the controllable switch Sa is turned off, as shown in Figure 6 The converter works in the secondary side resonant mode, that is, the leakage inductance Lk resonates with the secondary side resonant capacitor Cf1; the secondary side resonant mode can prevent the false turn-off of the secondary side rectifier switch SD. When the output load current is large, the controllable switch Sa is turned on, and the switchable capacitor Ca participates in the circuit operation, as shown in Figure 7 The converter can work in the primary side resonant mode, and during the resonant process, more energy is stored in the switchable capacitor Ca, reducing the energy stored in the clamp capacitor Cc when the main switch SL is turned off, which can effectively reduce the voltage stress of the main switch SL. Wherein, the controllable capacitor loop composed of the controllable switch Sa and the switchable capacitor Ca can be increased by one or more according to demand, so as to obtain more resonant combinations, so as to ensure the soft switching of the clamp switch SH, the main switch SL and the secondary side rectifier switch SD of the resonant state controllable active clamp flyback circuit.

[0037] For convenience of discussion, the secondary side resonant capacitor Cf1 and the controllable capacitor Ca are converted to the equivalent capacitor of the transformer primary side, which is denoted as Ceq. When the controllable switch Sa is turned off, Ceq=Cf1 / n2; when the controllable switch Sa is turned on, Ceq=(Cf1+Ca) / n2.

[0038] In the embodiment, during the operation of the active clamp flyback circuit with controllable resonant state, when the load current suddenly or gradually increases to a certain threshold, the controllable switch Sa is turned on, the switchable capacitor Ca starts to participate in the operation of the converter, the resonant state changes, and according to the size of the switchable capacitor Ca, Ceq=(Cf1+Ca) / n2 also changes. When Ceq is still much smaller than the clamp capacitor Cc, the circuit still operates in the secondary-side resonant state. When the order of magnitude of Ceq is the same as that of the clamp capacitor Cc, the circuit operates in the primary-secondary-side resonant mode. When Ceq is much larger than the clamp capacitor Cc, the circuit operates in the primary-side resonant mode. The above three cases all increase the capacitance participating in the resonance, thereby reducing the energy obtained by the clamp capacitor Cc, and achieving the effect of reducing the voltage stress of the main switch SL.

[0039] In summary, the active clamp flyback circuit with controllable resonant state reflects a case of changing the resonant state by using a controllable capacitor loop to achieve the system purpose. By increasing one or more controllable capacitor loops in the secondary side, the resonant state and resonant mode of the active clamp flyback converter are dynamically adjusted according to the input and output conditions of the system, that is, whether to switch the capacitor can be determined according to the change of the input and output quantity, and finally the realization of soft switching of the clamp switch SH, the main switch SL and the secondary rectifier switch SD, the reduction of the voltage stress of the main switch SL and the reduction of the output voltage ripple are achieved.

[0040] The above is only a preferred embodiment of the present application, and the protection scope of the present application is not limited to the above-mentioned embodiments. Any technical solution falling within the concept of the present application belongs to the protection scope of the present application.

Claims

1. A resonant state controllable active clamp flyback circuit, characterized in that, The voltage source, the clamping capacitor, the clamping switch tube loop, the main switch tube loop, the primary winding loop, the secondary winding loop, the secondary rectification switch tube loop, the controllable capacitor switching loop and the LC filter are included. The positive pole of the voltage source is electrically connected with one end of the clamping capacitor and the first end of the primary winding loop, the other end of the clamping capacitor is electrically connected with the first end of the clamping switch tube loop, the second end of the clamping switch tube loop is electrically connected with the second end of the primary winding loop and the first end of the main switch tube loop, the second end of the main switch tube loop is grounded, the secondary rectification switch tube loop is connected in series on the secondary winding loop, the controllable capacitor switching loop and the LC filter are connected in parallel on the secondary winding loop, and the LC filter is used to be connected with a load. The control end of the clamping switch tube loop, the control end of the main switch tube loop, the control end of the secondary rectification switch tube loop and the control end of the controllable capacitor switching loop are used to be electrically connected with the output end of a controller. The controllable capacitor switching loop includes a controllable switch tube and a switchable capacitor, one end of a secondary resonance capacitor is electrically connected with the source of the controllable switch tube, the drain of the controllable switch tube is electrically connected with one end of the switchable capacitor, the other end of the switchable capacitor is electrically connected with the other end of the secondary resonance capacitor, and the gate of the controllable switch tube is used to be electrically connected with the output end of a controller.

2. The resonant state controllable active clamp flyback circuit according to claim 1, characterized in that, The clamping switch tube loop includes a clamping switch tube and a clamping switch parasitic capacitor, the other end of the clamping capacitor is electrically connected with the drain of the clamping switch tube and one end of the clamping switch parasitic capacitor, the source of the clamping switch tube and the other end of the clamping switch parasitic capacitor are electrically connected with the second end of the primary winding loop, and the gate of the clamping switch tube is used to be electrically connected with the output end of a controller.

3. The resonant state controllable active clamp flyback circuit according to claim 1, characterized in that, The main switch tube loop includes a main switch tube and a main switch parasitic capacitor, the drain of the main switch tube and one end of the main switch parasitic capacitor are electrically connected with the second end of the primary winding loop, the source of the main switch tube and the other end of the main switch parasitic capacitor are grounded, and the gate of the main switch tube is used to be electrically connected with the output end of a controller.

4. The resonant state controllable active clamp flyback circuit according to claim 1, characterized in that, The primary winding loop includes an excitation inductor, a leakage inductor and a primary winding of a transformer, one end of the leakage inductor is electrically connected with the positive pole of the voltage source, the other end of the leakage inductor is electrically connected with one end of the excitation inductor and the same end of the primary winding, and the other end of the excitation inductor and the different end of the primary winding are electrically connected with the second end of the clamping switch tube loop.

5. The resonant state controllable active clamp flyback circuit according to claim 1, characterized in that, The secondary winding loop comprises a secondary winding of the transformer, a secondary resonance capacitor, a first end of the secondary resonance capacitor, a first end of the controllable capacitor switching loop, a first end of the LC filter, and a homonym end of the secondary winding are electrically connected, a homonym end of the secondary winding and a first end of the secondary rectification switch tube loop are electrically connected, a second end of the secondary rectification switch tube loop, a second end of the secondary resonance capacitor, a second end of the controllable capacitor switching loop, and a second end of the LC filter are electrically connected.

6. The resonant state controllable active clamp flyback circuit according to claim 5, characterized in that, The secondary rectification switch tube loop comprises a secondary rectification switch tube and a secondary rectification switch parasitic capacitor, a homonym end of the secondary winding, a drain of the secondary rectification switch tube, and one end of the secondary rectification switch parasitic capacitor are electrically connected, a source of the secondary rectification switch tube, the other end of the secondary rectification switch parasitic capacitor, and one end of the secondary resonance capacitor are electrically connected, and a gate of the secondary rectification switch tube is electrically connected with an output end of the controller.

7. The resonant state controllable active clamp flyback circuit according to claim 5, characterized in that, The LC filter comprises an output inductor and an output capacitor, one end of the secondary resonance capacitor and one end of the output inductor are electrically connected, the other end of the output inductor and one end of the output capacitor are electrically connected, the other end of the output capacitor and the other end of the secondary resonance capacitor are electrically connected, and the output capacitor is connected in parallel with the load.

8. A resonant state controllable active clamp flyback device, characterized by, The controller and the resonant state controllable active clamp flyback circuit according to any one of claims 1 to 7 are included, and an output end of the controller is electrically connected with control ends of the clamp switch tube loop, the primary switch tube loop, the secondary rectification switch tube loop, and the controllable capacitor switching loop.

Images