A forward-flyback hybrid circuit

Abstract

This invention discloses a hybrid forward / flyback circuit, including a primary-side switching circuit. The primary-side switching circuit includes a first primary-side switch and a second primary-side switch connected in series between the input voltage terminal and the primary-side reference ground, and a third primary-side switch and a fourth primary-side switch connected in series between the primary-side capacitor terminal and the primary-side reference ground. The connection point of the first and second primary-side switches is coupled to a first terminal of the primary winding of a transformer, and the connection point of the third and fourth primary-side switches is coupled to a second terminal of the primary winding. The hybrid forward / flyback circuit and its integrated transformer design of this invention combine forward energy transfer with flyback energy storage and release, achieving both high power transfer capability and low component count in a single topology, and significantly reducing the size of magnetic components through an integrated structure.

Description

Technical Field

[0001] This invention relates to electronic circuits. More specifically, this invention relates to a hybrid flyback / flyforward circuit. Background Technology

[0002] In the field of isolated small and medium power converters, forward converters and flyback converters are two commonly used technical solutions.

[0003] Traditional forward converters transfer energy to the load through direct coupling between the primary and secondary windings of a transformer. Their advantages include continuous output current and low output ripple during operation. However, forward converters require a magnetic reset circuit to prevent the magnetizing flux from accumulating in the transformer core and causing saturation. The magnetic reset circuit requires additional components and control, leading to a complex circuit structure and higher cost. Furthermore, the magnetic reset circuit itself incurs energy losses, limiting the converter's power density. In addition, forward converters must be equipped with a large secondary-side filter inductor to achieve continuous output current. Moreover, since energy is transferred directly through the transformer, the primary circuit cannot directly sample the output voltage; therefore, an isolated sampling circuit (such as an optocoupler) is typically added to the secondary circuit, further increasing the complexity of the system structure.

[0004] The working mechanism of a flyback converter differs from that of a forward converter. It transfers energy through the storage and release of energy in the magnetizing inductance of a transformer. Because the transformer simultaneously serves as both an energy storage inductor and an isolation transformer, the flyback converter requires fewer magnetic components than the forward converter, resulting in lower costs. However, flyback converters also have inherent limitations. For example, the transformer experiences a higher peak voltage when the switching transistor is on, leading to increased voltage stress on the transistor; the transformer flux exhibits a unidirectional waveform, utilizing only half of the core's BH curve, resulting in low core utilization; and the flyback energy is released only during the switching transistor's off-state, resulting in discontinuous output current, larger ripple, and significant noise, affecting the system's electromagnetic interference (EMI) performance and dynamic response.

[0005] Therefore, it is necessary to propose a new topology that can effectively combine the advantages of both forward and flyback converters. Summary of the Invention

[0006] This application proposes a hybrid forward / flyback circuit and a magnetically integrated transformer design. By combining forward energy transfer with flyback energy storage and release, it simultaneously achieves the advantages of high power transfer capability and low component count in a single topology, and significantly reduces the size of magnetic components through the magnetically integrated structure. Furthermore, the primary-side sampling mechanism of this invention can accurately adjust the output voltage without relying on isolation devices such as optocouplers, thereby improving reliability.

[0007] According to an embodiment of the present invention, a hybrid flyback / forward circuit is provided, comprising: a primary-side switching circuit including a first primary-side switch, a second primary-side switch, a third primary-side switch, and a fourth primary-side switch. The first and second primary-side switches are connected in series between an input voltage terminal and a primary-side reference ground. The third and fourth primary-side switches are connected in series between a primary-side capacitor terminal and a primary-side reference ground. The connection point of the first and second primary-side switches is coupled to a first terminal of the primary winding of a transformer. The connection point of the third and fourth primary-side switches is coupled to a second terminal of the primary winding of the transformer. The primary-side capacitor terminal is coupled to one terminal of a primary-side capacitor.

[0008] In one embodiment, the aforementioned flyback hybrid circuit further includes a primary-side capacitor coupled between the primary-side capacitor terminal and the primary-side reference ground.

[0009] In one embodiment, the aforementioned flyback hybrid circuit further includes: a transformer having a primary winding, a first secondary winding, and a second secondary winding; and a secondary inductor coupled to the first secondary winding and the second secondary winding via a secondary switching circuit.

[0010] In one embodiment, the aforementioned transformer and secondary inductor are integrated into an integrated transformer, the integrated transformer comprising: an E-shaped structure having a middle post and side posts, wherein the primary winding, the first secondary winding and the second secondary winding of the transformer are wound on the middle post, and the secondary inductor is wound on one of the side posts; and an I-shaped structure having an air gap between the middle post and the side post of the E-shaped structure.

[0011] In one embodiment, the aforementioned flyback hybrid circuit has repeating switching cycles, wherein each switching cycle includes: a first switching interval in which the first primary-side switch and the fourth primary-side switch are turned on, and the second primary-side switch and the third primary-side switch are turned off; a second switching interval in which the second primary-side switch and the third primary-side switch are turned on, and the first primary-side switch and the fourth primary-side switch are turned off; and a third switching interval in which the second primary-side switch and the fourth primary-side switch are turned on, and the first primary-side switch and the third primary-side switch are turned off.

[0012] In one embodiment, the aforementioned flyback hybrid circuit further includes a secondary-side switching circuit coupled to a first secondary winding and a second secondary winding. The secondary-side switching circuit includes: a first secondary-side switch having a first end coupled to a first end of the first secondary winding and a second end coupled to an output voltage terminal; a second secondary-side switch having a first end coupled to a second end of the second secondary winding and a second end coupled to a first end of a secondary inductor, the second end of the secondary inductor being coupled to the output voltage terminal; and a third secondary-side switch having a first end coupled to a secondary-side reference ground and a second end coupled to a second end of the second secondary-side switch; wherein the second end of the first secondary winding and the first end of the second secondary winding are coupled to the secondary-side reference ground, and the first end of the primary winding, the second end of the first secondary winding, and the second end of the second secondary winding are terminals of the same name.

[0013] In one embodiment, the aforementioned flyback-forward hybrid circuit further includes a secondary-side switching circuit coupled to a first secondary winding and a second secondary winding. The secondary-side switching circuit includes: a first secondary-side switch having a first end coupled to a secondary-side reference ground and a second end coupled to a second end of the first secondary winding; a second secondary-side switch having a first end coupled to a first end of a secondary inductor and a second end coupled to a first end of the second secondary winding, the second end of the secondary inductor being coupled to the secondary-side reference ground; and a third secondary-side switch having a first end coupled to the first end of the second secondary switch and a second end coupled to an output voltage terminal. The second end of the second secondary winding and the first end of the first secondary winding are coupled to the output voltage terminal, and the first end of the primary winding, the second end of the first secondary winding, and the second end of the second secondary winding are terminals of the same name.

[0014] In one embodiment, the aforementioned flyback hybrid circuit further includes a voltage detection circuit having an input terminal coupled to the primary-side capacitor terminal and an output terminal providing a voltage detection signal characterizing the output voltage of the flyback hybrid circuit.

[0015] In one embodiment, the aforementioned flyback-flyback hybrid circuit further includes a control circuit that, based on a voltage detection signal, outputs a first primary-side switch control signal, a second primary-side switch control signal, a third primary-side switch control signal, and a fourth primary-side switch control signal to control the on / off states of the first primary-side switch, the second primary-side switch, the third primary-side switch, and the fourth primary-side switch, respectively. Attached Figure Description

[0016] The above and other objects, features and advantages of this application will become clearer from the following description of embodiments with reference to the accompanying drawings:

[0017] Figure 1 This is a schematic diagram of the circuit structure of a flyback-flyback hybrid circuit 10 according to an embodiment of this application;

[0018] Figure 2This is a schematic diagram of the signal waveforms of a flyback-flyback hybrid circuit 10 according to an embodiment of this application;

[0019] Figure 3 This is a schematic diagram of the equivalent circuit structure of the flyback-flyback hybrid circuit 10 according to an embodiment of this application when it is operating in the first switching interval;

[0020] Figure 4 This is a schematic diagram of the equivalent circuit structure of the flyback-flyback hybrid circuit 10 according to an embodiment of this application when it operates in the second switching interval;

[0021] Figure 5 This is a schematic diagram of the equivalent circuit structure of the flyback-flyback hybrid circuit 10 according to an embodiment of this application when it is operating in the third switching interval;

[0022] Figure 6 This is a schematic diagram of the structure of an integrated transformer 60 according to an embodiment of this application;

[0023] Figure 7 This is a schematic diagram of the circuit structure of a flyback-flyback hybrid circuit 70 according to an embodiment of this application. Detailed Implementation

[0024] Specific embodiments of the present invention will now be described in detail. It should be noted that the embodiments described herein are for illustrative purposes only and are not intended to limit the invention. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the invention. However, it will be apparent to those skilled in the art that these specific details are not necessary to practice the invention. In other instances, well-known circuits, materials, or methods have not been specifically described to avoid obscuring the invention.

[0025] The terms "first," "second," etc., used in the following description are for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature specified with "first," "second," etc., may explicitly or implicitly include one or more of that feature. In the description of this application, unless otherwise stated, "multiple" means two or more.

[0026] In this application, unless otherwise expressly specified and limited, the term "connection" should be interpreted broadly. For example, "connection" can be a fixed connection, a detachable connection, or an integral part; it can be a direct connection or an indirect connection through an intermediate medium. Furthermore, the term "coupled" can refer to a method of electrical connection for signal transmission. "Coupled" can be a direct electrical connection or an indirect electrical connection through an intermediate medium.

[0027] Figure 1 This is a schematic diagram of the circuit structure of a flyback-forward hybrid circuit 10 according to an embodiment of this application. Figure 1As shown, the flyback-flyback hybrid circuit 10 includes a transformer T1, a primary-side switching circuit 101, a primary-side capacitor Cd, a secondary-side switching circuit 102, and a secondary-side inductor Lf.

[0028] Transformer T1 includes a primary winding Np, a first secondary winding Ns1, and a second secondary winding Ns2. Figure 1 The inductance Lr shown represents the leakage inductance of transformer T1, and the inductance Lm represents the magnetizing inductance of transformer T1. Figure 1 In this embodiment, the inductance Lr is the parasitic inductance of transformer T1 and does not represent an actual circuit device. In some embodiments, to better achieve the soft-switching function, when the leakage inductance of transformer T1 is insufficient, the leakage inductance Lr can be increased by adding an actual inductor. Therefore, in some embodiments, the inductance Lr can also represent an actual inductor.

[0029] The primary-side switching circuit 101 includes a first primary-side switch M1, a second primary-side switch M2, a third primary-side switch M3, and a fourth primary-side switch M4. The first primary-side switch M1 and the second primary-side switch M2 are connected in series between the input voltage terminal IN1 and the primary-side reference ground PGND. The third primary-side switch M3 and the fourth primary-side switch M4 are connected in series between the primary-side capacitor terminal Tc and the primary-side reference ground GND. The primary-side capacitor Cd is coupled between the primary-side capacitor terminal Tc and the primary-side reference ground GND. The connection point of the first primary-side switch M1 and the second primary-side switch M2 is coupled to the first terminal A of the primary-side winding Np. The connection point of the third primary-side switch M3 and the fourth primary-side switch M4 is coupled to the second terminal B of the primary-side winding Np. The primary-side switches M1-M4 may include controllable switching transistors such as MOSFETs.

[0030] The secondary-side switching circuit 102 is coupled to the first secondary-side winding Ns1 and the second secondary-side winding Ns2. The secondary-side inductor Lf is coupled to the first secondary-side winding Ns1 and the second secondary-side winding Ns2 through the secondary-side switching circuit 102.

[0031] exist Figure 1 In this embodiment, the secondary-side switching circuit 102 includes a first secondary-side switch D1, a second secondary-side switch D2, and a third secondary-side switch D3. The first secondary-side switch D1 has a first terminal coupled to a first terminal C of a first secondary-side winding Ns1, and a second terminal coupled to an output voltage terminal OUT1. The second secondary-side switch D2 has a first terminal coupled to a second terminal D of a second secondary-side winding Ns2, and a second terminal coupled to a first terminal E of a secondary-side inductor Lf. The second terminal F of the secondary-side inductor Lf is coupled to the output voltage terminal OUT1. The third secondary-side switch D3 has a first terminal coupled to the secondary-side reference ground SGND, and a second terminal coupled to a second terminal of the second secondary-side switch D2. The second terminal of the first secondary-side winding Ns1 and the first terminal of the second secondary-side winding Ns2 are coupled together to form an intermediate terminal G, which is coupled to the secondary-side reference ground SGND. Figure 1In this embodiment, the first end A of the primary winding Np, the second end (the middle end G) of the first secondary winding Ns1, and the second end D of the second secondary winding Ns2 are terminals of the same name. Figure 1 In this embodiment, the secondary switches D1-D3 include diodes. In other embodiments, the secondary switches D1-D3 may also include controllable switching transistors. When the secondary switches D1-D3 are diodes, the first terminal of each secondary switch D1-D3 is the anode of the diode, and the second terminal is the cathode of the diode. When the secondary switches D1-D3 are controllable switching transistors, such as N-type MOSFETs, the first terminal of each secondary switch D1-D3 is the drain of the N-type MOSFET, and the second terminal is the source of the N-type MOSFET.

[0032] exist Figure 1 In this circuit, the flyback-flyback hybrid circuit 10 is powered by a power supply Vi, which provides energy to the load represented by the resistor RL. For simplicity, Vi also represents the input voltage of the flyback-flyback hybrid circuit 10. The power supply Vi is coupled between the input voltage terminals IN1 and IN2, where the input voltage terminal IN2 is coupled to the primary-side reference ground PGND. The power supply Vi can be provided by an external power supply or by the preceding circuitry. The output capacitor Co is coupled between the output voltage terminals OUT1 and OUT2 for filtering, where the output voltage terminal OUT2 is coupled to the secondary-side reference ground SGND. The output capacitor Co can be integrated with the flyback-flyback hybrid circuit 10 or can be a discrete device.

[0033] Figure 1 The flyback-forward hybrid circuit 10 of the embodiment further includes a control circuit 103. This control circuit 103 includes a voltage detection circuit 1031. The voltage detection circuit 1031 detects the voltage Vcd across the primary-side capacitor Cd to obtain a voltage detection signal Vs characterizing the output voltage VOUT. Based on this voltage detection signal Vs, the control circuit 103 outputs a first primary-side switch control signal G1, a second primary-side switch control signal G2, a third primary-side switch control signal G3, and a fourth primary-side switch control signal G4, which are used to control the on / off states of primary-side switches M1-M4, thereby adjusting the output voltage Vo.

[0034] Figure 2 This is a schematic diagram of the signal waveforms of a flyback-flyback hybrid circuit 10 according to an embodiment of this application. Figure 3 , Figure 4 and Figure 5 This is a schematic diagram of the equivalent circuit structure of the flyback-flyback hybrid circuit 10 according to an embodiment of this application when it operates in different switching ranges. The following will be combined with... Figures 1-5 The working principle of the flyback-flyback hybrid circuit 10 in the embodiments of this application will be explained.

[0035] In the flyback-flyback hybrid circuit 10, the first primary-side switch M1 and the second primary-side switch M2 are alternately switched on and off, as are the third primary-side switch M3 and the fourth primary-side switch M4. When the flyback-flyback hybrid circuit 10 is operating normally, the primary-side switches M1-M4 are periodically switched on and off. Each switching cycle includes a first switching interval, a second switching interval, a third switching interval, and a ZVS (Zero Voltage Switching) interval between each switching interval, such as... Figure 2 As shown.

[0036] In the first switching interval t1-t2, the first primary-side switch M1 and the fourth primary-side switch M4 are turned on, while the second primary-side switch M2 and the third primary-side switch M3 are turned off. The equivalent circuit is as follows: Figure 3 As shown. Within this switching interval, the power supply Vi energizes the transformer T1, and the energizing current iLm flowing through the energizing inductor Lm rises and reaches its peak value Ipk. Simultaneously, energy is transferred to the load RL through the transformer T1 and the second secondary switch D2. During this process, the current iD2 flowing through the second secondary switch D2 rises, and the secondary inductor Lf stores energy.

[0037] In the second switching interval t3-t4, the second primary-side switch M2 and the third primary-side switch M3 are turned on, while the first primary-side switch M1 and the fourth primary-side switch M4 are turned off. The equivalent circuit is as follows: Figure 4 As shown. Within this switching interval, transformer T1 undergoes magnetic reset, and the magnetizing current iLm flowing through the magnetizing inductor Lm decreases. The secondary inductor Lf supplies power to the load through the third secondary switch D3, and transfers energy to the primary side to charge the primary capacitor Cd through the first secondary switch D1 and the first secondary winding Ns1. At this time, the output voltage Vo is induced to the primary capacitor Cd through transformer T1, and the voltage across the primary capacitor Cd is Vcd = (Np / Ns1) × Vo, where Np also represents the number of turns in the primary winding Np, Ns1 also represents the number of turns in the first secondary winding Ns1, and Vo is the output voltage value. Thus, the output voltage Vo can be detected on the primary side without using coupling devices or other voltage detection circuits. Figure 1 In this embodiment, the voltage Vcd across the primary capacitor Cd is provided to the control circuit 103 and participates in the control of the primary switches M1-M4.

[0038] In the third switching interval t5-t6, the second primary-side switch M2 and the fourth primary-side switch M4 are turned on, while the first primary-side switch M1 and the third primary-side switch M3 are turned off. The equivalent circuit is as follows: Figure 5 As shown. At this time, the primary current iLr of transformer T1 is negative and clamped. This negative current is used for the soft switching of the first primary switch M1 at the beginning of the next switching cycle (time t7).

[0039] like Figure 2As shown, between the first switching interval t1-t2, the second switching interval t3-t4, and the third switching interval t5-t6, there are also ZVS intervals Tzvs1, Tzvs2, and Tzvs3. ZVS interval Tzvs1 is between time t0-t1. At this time, the current iLr flowing through the primary winding Np is a negative current Ineg. This negative current Ineg charges the first terminal A of the primary winding Np, so that before the first primary switch M1 is turned on, the voltage Va at the first terminal A of the primary winding Np is close to the input voltage Vi, achieving zero-voltage conduction of the first primary switch M1. ZVS interval Tzvs2 is between time t2-t3. At this time, the first primary switch M1 and the fourth primary switch M4 are turned off, while the second primary switch M2 and the third primary switch M3 are not yet turned on, and the current iLr flowing through the primary winding Np reaches its peak value. The current iLr discharges at terminal A of the primary winding Np and simultaneously charges terminal B of the primary winding Np. This causes the voltage Va at terminal A of the primary winding Np to be close to the voltage of the primary reference ground PGND before the second primary switch M2 and the third primary switch M3 are turned on, and the voltage Vb at terminal B of the primary winding Np to be close to the primary capacitor voltage Vcd. This achieves zero-voltage conduction of the second primary switch M2 and the third primary switch M3. The ZVS interval Tzvs3 is between time t4 and t5. At this time, the current iLr flowing through the primary winding Np is a negative current Ineg. This negative current Ineg discharges at terminal B of the primary winding Np, causing the voltage Vb at terminal B of the primary winding Np to be close to the voltage of the primary reference ground PGND before the fourth primary switch M4 is turned on, achieving zero-voltage conduction of the fourth primary switch M1. The structure of the flyback-flyback hybrid circuit in this application embodiment effectively achieves zero-voltage conduction of each primary-side switch, reduces switching losses, and improves circuit efficiency.

[0040] Figure 6 This is a schematic diagram of the structure of an integrated transformer 60 according to an embodiment of this application. The integrated transformer 60 integrates, for example... Figure 1 The transformer T1 and secondary inductor Lf are shown. The integrated transformer 60 includes an E-shaped structure 601 and an I-shaped structure 602. The E-shaped structure 601 includes a middle post and side posts, and there is an air gap between the E-shaped structure 601 and the I-shaped structure 602. The primary winding Np, the first secondary winding Ns1, and the second secondary winding Ns2 are wound on the middle post of the E-shaped structure 601, and the secondary inductor Lf is wound on one of the side posts. Figure 6As shown, the magnetic flux directions of the primary winding Np and the first secondary winding Ns1 are aligned, and opposite to the magnetic flux direction of the second secondary winding Ns2. The secondary inductor Lf and the windings of the transformer T1 are located on different magnetic pillars and integrated into a single magnetic element structure. Applying the integrated transformer 60 to the flyback hybrid circuit 10 reduces the number and size of circuit components. The integrated transformer can also have other structures, such as a double-E structure. Furthermore, the directions of the windings can be varied while maintaining alignment with the magnetic flux direction of the primary winding Np and the second secondary winding Ns1. Figure 6 Under the premise that the magnetic flux direction relationship of each winding is consistent in the embodiment, it can be used for Figure 1 The embodiment of the flyback-flyback hybrid circuit.

[0041] Figure 7 This is a schematic diagram of the circuit structure of a flyback / flyforward hybrid circuit 70 according to an embodiment of this application. Figure 7 As shown, the flyback-flyback hybrid circuit 70 includes a transformer T1, a primary-side switching circuit 101, a primary-side capacitor Cd, a secondary-side switching circuit 702, and a secondary-side inductor Lf.

[0042] and Figure 1 Compared to the previous examples, Figure 7 The secondary-side switching circuit 702 of the flyback-reverse hybrid circuit 70 includes a first secondary-side switch D1, a second secondary-side switch D2, and a third secondary-side switch D3. The first secondary-side switch D1 has a first terminal coupled to the secondary-side reference ground SGND and a second terminal coupled to the second terminal C of the first secondary-side winding Ns1. The second secondary-side switch D2 has a first terminal coupled to the first terminal E of the secondary-side inductor Lf and a second terminal coupled to the first terminal D of the second secondary-side winding Ns2. The second terminal F of the secondary-side inductor Lf is coupled to the secondary-side reference ground SGND. The third secondary-side switch D3 has a first terminal coupled to the first terminal of the second secondary-side switch D2 and a second terminal coupled to the output voltage terminal OUT1. The first terminal of the first secondary-side winding Ns1 and the second terminal of the second secondary-side winding Ns2 are coupled together to form an intermediate terminal G, which is coupled to the output voltage terminal OUT1. Figure 7 In the embodiment, the first end A of the primary winding Np, the second end (i.e., the middle end G) of the second secondary winding Ns2, and the second end C of the first secondary winding Ns1 are the same end.

[0043] The working principle of the flyback-flyback hybrid circuit 70 is similar to that of the flyback-flyback hybrid circuit 10, and will not be elaborated here for the sake of brevity.

[0044] In summary, the hybrid flyback / forward circuit provided in this application does not require the reset circuit necessary for a forward topology, thus significantly reducing the number of components and the overall size of the circuit. The hybrid flyback / forward circuit of this application simultaneously achieves direct energy transfer and energy storage / release in two intervals within a single switching cycle, resulting in a significantly improved output capability compared to conventional flyback circuits, while maintaining low ripple and good transient performance.

[0045] Secondly, the hybrid flyback / flyback circuit of this application embodiment possesses primary-side feedback capability, which simplifies the feedback circuit. In the magnetic reset region, the primary-side capacitor voltage directly maps to the output voltage. By acquiring this voltage, the output voltage can be calculated, eliminating the need for an optocoupler-isolated feedback circuit on the secondary side, thus achieving precise output voltage regulation. This primary-side feedback mechanism not only further simplifies the system structure and reduces costs but also significantly improves system reliability and lifespan, making it particularly suitable for applications with extremely high space and reliability requirements.

[0046] Furthermore, the integration technology achieves high power density. The integrated transformer in this application embodiment concentrates the functions that traditionally require two independent magnetic elements into a single magnetic element, greatly reducing the total number and volume of magnetic elements and solving the fundamental bottleneck restricting the improvement of power density.

[0047] In summary, the flyback-flyback hybrid circuit of this application embodiment can significantly improve power density, efficiency and system reliability without increasing the number of components.

[0048] The above description is merely a preferred embodiment of this application and is not intended to limit the application in any way. Although this application has disclosed preferred embodiments above, it is not intended to limit the application. Any person skilled in the art can make many possible variations and modifications to the technical solutions of this application using the methods and techniques disclosed above, or modify them into equivalent embodiments with equivalent changes, without departing from the scope of the technical solutions of this application. Therefore, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of this application without departing from the content of the technical solutions of this application shall still fall within the protection scope of the technical solutions of this application.

Claims

1. A hybrid forward / flyback circuit, comprising: The primary-side switching circuit includes a first primary-side switch, a second primary-side switch, a third primary-side switch, and a fourth primary-side switch. The first and second primary-side switches are connected in series between the input voltage terminal and the primary-side reference ground. The third and fourth primary-side switches are connected in series between the primary-side capacitor terminal and the primary-side reference ground. The connection point of the first and second primary-side switches is coupled to the first terminal of the primary winding of the transformer. The connection point of the third and fourth primary-side switches is coupled to the second terminal of the primary winding of the transformer. The primary-side capacitor terminal is coupled to one end of a primary-side capacitor.

2. The hybrid forward / flyback circuit as described in claim 1, further comprising: The primary capacitor is coupled between the primary capacitor terminal and the primary reference ground.

3. The hybrid forward / flyback circuit as described in claim 1, further comprising: A transformer has a primary winding, a first secondary winding, and a second secondary winding; as well as The secondary inductor is coupled to the first and second secondary windings via a secondary switching circuit.

4. The forward and flyback hybrid circuit of claim 3, wherein, The transformer and the secondary inductor are integrated into an integrated transformer, which includes: The transformer has an E-shaped structure with a middle post and side posts. The primary winding, the first secondary winding, and the second secondary winding are wound around the middle post, and the secondary inductor is wound around one of the side posts. The I-shaped structure has air gaps between the central and side columns of the E-shaped structure.

5. The forward and flyback hybrid circuit of claim 4, wherein, The magnetic flux direction of the primary winding and the first secondary winding is consistent, while the magnetic flux direction of the second secondary winding is opposite.

6. The forward / flyback hybrid circuit of claim 3 further includes a secondary-side switching circuit coupled to the first secondary winding and the second secondary winding, wherein the secondary-side switching circuit includes: The first secondary switch has a first end coupled to the first end of the first secondary winding and a second end coupled to the output voltage terminal; as well as The second secondary switch has a first end coupled to the second end of the second secondary winding, a second end coupled to the first end of the secondary inductor, and the second end of the secondary inductor coupled to the output voltage terminal; as well as The third secondary switch has a first end coupled to the secondary reference ground and a second end coupled to the second end of the second secondary switch; The second end of the first secondary winding and the first end of the second secondary winding are coupled to the secondary reference ground, and the first end of the primary winding, the second end of the first secondary winding and the second end of the second secondary winding are terminals with the same name.

7. The forward / flyback hybrid circuit of claim 3 further includes a secondary-side switching circuit coupled to the first secondary winding and the second secondary winding, wherein the secondary-side switching circuit includes: The first secondary switch has a first end coupled to the secondary reference ground and a second end coupled to the second end of the first secondary winding; The second secondary switch has a first end coupled to a first end of a secondary inductor and a second end coupled to a first end of a second secondary winding, wherein the second end of the secondary inductor is coupled to a secondary reference ground. The third secondary switch has a first terminal coupled to the first terminal of the second secondary switch and a second terminal coupled to the output voltage terminal; The second end of the second secondary winding and the first end of the first secondary winding are coupled to the output voltage terminal, and the first end of the primary winding, the second end of the first secondary winding and the second end of the second secondary winding are terminals with the same name.

8. The hybrid flyback / flyforward circuit as described in claim 6 or 7, wherein: The first secondary switch, the second secondary switch, and the third secondary switch each include a diode. The first terminal of the first secondary switch, the second secondary switch, and the third secondary switch is the anode terminal of each diode, and the second terminal is the cathode terminal of each diode.

9. The hybrid flyback / forward circuit as described in claim 1, wherein: The first primary-side switch, the second primary-side switch, the third primary-side switch, and the fourth primary-side switch include MOSFETs.

10. The flyback-flyback hybrid circuit of claim 1, having repeating switching cycles, wherein each switching cycle includes: In the first switching interval, the first primary-side switch and the fourth primary-side switch are turned on, while the second primary-side switch and the third primary-side switch are turned off. In the second switching interval, the second primary-side switch and the third primary-side switch are turned on, and the first primary-side switch and the fourth primary-side switch are turned off. as well as In the third switching interval, the second primary-side switch and the fourth primary-side switch are turned on, while the first primary-side switch and the third primary-side switch are turned off.

11. The hybrid forward / flyback circuit as described in claim 1, further comprising: The voltage detection circuit has an input terminal coupled to the primary capacitor terminal and an output terminal providing a voltage detection signal characterizing the output voltage of the flyback hybrid circuit.

12. The flyback-flyback hybrid circuit of claim 11, further comprising: The control circuit, based on the voltage detection signal, outputs a first primary-side switch control signal, a second primary-side switch control signal, a third primary-side switch control signal, and a fourth primary-side switch control signal, which control the on / off state of the first primary-side switch, the second primary-side switch, the third primary-side switch, and the fourth primary-side switch, respectively.

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