Hybrid flyback circuit and control method

Abstract

The present disclosure relates to a hybrid flyback circuit and a control method. The hybrid flyback circuit includes: an upper-arm and a lower-arm switch; a transformer; a resonant circuit; a sampling circuit that samples the primary current of the transformer and outputs a sampling signal; a control unit, which includes: an output voltage feedback unit that generates a first feedback signal based on a reference voltage and an output voltage; a peak current comparison unit that turns off the upper-arm switch when the sampling signal is equal to the first feedback signal; a first dead-time delay unit that turns on the lower-arm switch after the upper-arm switch is turned off and after a first dead time; a negative peak current feedback unit that generates a second feedback signal based on a negative peak current value and a reference current; a conduction control unit that controls the turning off of the lower-arm switch based on the second feedback signal; a second dead-time delay unit that turns on the upper-arm switch after the lower-arm switch is turned off and after a second dead time.

Description

Technical Field

[0001] The present disclosure relates to a hybrid flyback circuit, and particularly to a hybrid flyback circuit and a control method that take into account output dynamic response and efficiency. Background Art

[0002] Research in recent years has found that the hybrid flyback circuit has excellent characteristics similar to those of the LLC resonant converter, that is, the primary-side switch of the hybrid flyback circuit is turned on with zero voltage (ZVS), and the secondary-side switch of the hybrid flyback circuit is turned off with zero current (ZCS). At the same time, the hybrid flyback circuit also has good ability to regulate the output voltage, so it is suitable for USB PD Type-C applications.

[0003] The hybrid flyback circuit usually includes a resonant circuit, a half-bridge switch circuit, a transformer, and a rectifier circuit, and the resonant circuit also includes a resonant inductor and a resonant capacitor, etc. When the hybrid flyback circuit starts to work, in order to achieve zero-voltage turn-on of the upper-arm switch of the half-bridge switch circuit, the magnetizing current in the magnetizing inductor needs to rise from a negative peak value, and the negative peak value needs to be large enough to achieve zero-voltage turn-on. However, once the negative peak value is too large, it will cause additional losses in the hybrid flyback circuit, thereby reducing the efficiency of the hybrid flyback circuit. Therefore, how to precisely control the negative peak value of the magnetizing current so that it can exactly achieve zero-voltage turn-on of the upper-arm switch of the half-bridge switch circuit is the key to the optimization control of the hybrid flyback circuit.

[0004] In order to control the magnitude of the negative peak value of the magnetizing current, the control strategy of the traditional hybrid flyback circuit is to perform in an adaptive successive approximation manner, that is, turn off the upper-arm switch of the half-bridge switch circuit, and after the dead time, turn on the lower-arm switch of the half-bridge switch circuit with zero voltage. The turn-off moment of the lower-arm switch of the half-bridge switch circuit is adaptively adjusted by detecting whether the turn-on moment of the upper-arm switch is zero-voltage turn-on. The specific method of adaptive adjustment is that after the lower-arm switch is turned off, directly or indirectly detect whether the upper-arm switch can achieve zero-voltage turn-on after the dead time. If the upper-arm switch cannot achieve zero-voltage turn-on, the turn-on time of the lower-arm switch in the next switching period will increase by a regulation unit time on the basis of the previous switching period, so as to increase the negative peak value of the magnetizing current, thereby achieving zero-voltage turn-on of the upper-arm switch. After going through one or more switching periods like this, the upper-arm switch can finally achieve zero-voltage turn-on. In addition, if the upper-arm switch can already achieve zero-voltage turn-on, the turn-on time of the lower-arm switch in the next switching period will decrease by a regulation unit time on the basis of the previous switching period, so as to reduce the negative peak value of the magnetizing current. After going through one or more switching periods like this, the upper-arm switch can finally get out of the condition of zero-voltage turn-on. Finally, the negative peak value of the magnetizing current can be dynamically maintained near the ideal value required to achieve zero-voltage turn-on of the half-bridge switch circuit.

[0005] Although the traditional control method of the above-mentioned hybrid flyback circuit can achieve zero-voltage turn-on and control the negative peak value of the magnetizing current near the ideal value, it also has obvious disadvantages. First, only when the output current of the hybrid flyback circuit is constant can the negative peak value of the magnetizing current always be maintained near the ideal value. Once the output current changes, the negative peak value of the magnetizing current will change, resulting in the need to go through another dynamic adjustment of the negative peak value to return to the ideal value. In terms of dynamic adjustment, if the selected adjustment unit time is small, the same current value deviation requires more switching cycles to adjust the negative peak value of the magnetizing current to the ideal value. If the output current of the hybrid flyback circuit is in a fast dynamic process, the adjustment speed of the negative peak value of the magnetizing current will not be able to meet the dynamic requirements of the hybrid flyback circuit, resulting in a decline in the performance of the hybrid flyback circuit. On the contrary, if the selected adjustment unit time is large, although the adjustment speed of the negative peak value of the magnetizing current can be increased, it will also cause the finally adjusted negative peak value of the magnetizing current to deviate greatly from its ideal value, affecting the steady-state efficiency.

[0006] Therefore, how to develop a hybrid flyback circuit and control method that overcomes the above disadvantages is an urgent need at present. Summary of the Invention

[0007] The purpose of the present disclosure is to provide a hybrid flyback circuit and a control method. The hybrid flyback circuit can meet the requirements of output dynamics and achieve good steady-state efficiency at the same time.

[0008] To achieve the above object, a broader embodiment of the present disclosure provides a hybrid flyback circuit, comprising: a half-bridge switching circuit including an upper-arm switch and a lower-arm switch connected in series; a transformer including a primary winding and a secondary winding; a resonant circuit connected in series with the primary winding; a current sampling circuit for sampling the primary current of the transformer and outputting a current sampling signal; a rectifying circuit connected to the secondary winding; and a control unit for controlling the operation of the half-bridge switching circuit, and comprising: an output voltage feedback unit for generating a first voltage feedback signal according to a reference voltage and the output voltage output by the hybrid flyback circuit; a peak current comparison unit for comparing the current sampling signal and the first voltage feedback signal, and driving the control unit to control the upper-arm switch to turn off when the current sampling signal is equal to the first voltage feedback signal; a first dead-time delay unit for driving the control unit to control the lower-arm switch to turn on after the upper-arm switch turns off and after a first dead-time; a negative peak current feedback unit for obtaining a negative peak current value of the primary current according to the current sampling signal, and generating a second voltage feedback signal according to the negative peak current value and a reference current; a conduction control unit for controlling the conduction time length of the lower-arm switch according to the second voltage feedback signal, and driving the control unit to control the lower-arm switch to turn off; and a second dead-time delay unit for driving the control unit to control the upper-arm switch to turn on after the lower-arm switch turns off and after a second dead-time.

[0009] To achieve the above object, another broader embodiment of the present disclosure provides a control method applied to a hybrid flyback circuit, wherein the hybrid flyback circuit further comprises a half-bridge switching circuit, a transformer, a resonant circuit, and a current sampling circuit. The half-bridge switching circuit includes an upper-arm switch and a lower-arm switch, the transformer includes a primary winding and a secondary winding, and the resonant circuit is connected in series with the primary winding. The control method comprises: (S1) sampling the output voltage output by the hybrid flyback circuit, and generating a first voltage feedback signal according to a reference voltage and the output voltage; (S2) sampling the primary current of the transformer and outputting a current sampling signal; (S3) comparing the current sampling signal and the first voltage feedback signal, and controlling the upper-arm switch to turn off when the current sampling signal is equal to the first voltage feedback signal; (S4) controlling the lower-arm switch to turn on after the upper-arm switch turns off and after a first dead-time; (S5) obtaining a negative peak current value of the primary current according to the current sampling signal, and generating a second voltage feedback signal according to the negative peak current value and a reference current; (S6) controlling the conduction time length of the lower-arm switch according to the second voltage feedback signal, and controlling the lower-arm switch to turn off; and (S7) controlling the upper-arm switch to turn on after the lower-arm switch turns off and after a second dead-time. Description of the Drawings

[0010] Figure 1 Schematic diagram of the circuit architecture of the hybrid flyback circuit according to a preferred embodiment of the present disclosure;

[0011] Figure 2 For Figure 1 the voltage and current timing schematic diagram of the hybrid flyback circuit shown;

[0012] Figure 3 shows Figure 1 the detailed circuit structure schematic diagram of the conduction control unit of the hybrid flyback circuit shown;

[0013] Figure 4 This is for the application of the preferred embodiment of the present disclosure to Figure 1 the step flow schematic diagram of the control method in the control unit of the hybrid flyback circuit shown.

[0014] Symbol description

[0015] 1: Hybrid flyback circuit

[0016] V in : Input voltage

[0017] V o : Output voltage

[0018] 2: Half-bridge switch circuit

[0019] T r : Transformer

[0020] 3: Resonant circuit

[0021] 4: Current sampling circuit

[0022] 5: Rectifier circuit

[0023] 6: Control unit

[0024] S1: Upper-arm switch

[0025] S2: Lower-arm switch

[0026] N p : Primary winding

[0027] N s : Secondary winding

[0028] C r : Resonant capacitor

[0029] L r : Resonant inductor

[0030] L m : Magnetizing inductor

[0031] I Lr : Current sampling signal

[0032] S R : Rectifier switch

[0033] Co : Output capacitor

[0034] 60: Output voltage feedback unit

[0035] 61: Peak current comparison unit

[0036] 62: First dead time delay unit

[0037] 63: Negative peak current feedback unit

[0038] 64: Conduction control unit

[0039] 65: Second dead time delay unit

[0040] V o_ref : Reference voltage

[0041] V FB : First voltage feedback signal

[0042] S 1off 、S 2off : Turn-off control signal

[0043] S 1on 、S 2on : Turn-on control signal

[0044] I neg_ref : Reference current

[0045] V Ineg : Second voltage feedback signal

[0046] C oss1 : First parasitic capacitance

[0047] C oss2 : Second parasitic capacitance

[0048] 66: Current holding unit

[0049] T: Second set time

[0050] i Lr : Current flowing through the resonant inductor

[0051] i Lm : Current flowing through the resonant inductor

[0052] 640: Conduction comparison unit

[0053] 641: Conduction timing unit

[0054] S1~S7: Step flow of the control method Specific implementation manner

[0055] Some exemplary embodiments embodying the features and advantages of the present disclosure will be described in detail in the following description. It should be understood that the present disclosure can have various variations in different embodiments, all of which do not depart from the scope of the present disclosure, and the descriptions and drawings therein are essentially for illustrative purposes and not for limiting the present disclosure.

[0056] Please refer to Figure 1 and Figure 2 , Figure 1 , which is a schematic diagram of the circuit architecture of the hybrid flyback circuit according to a preferred embodiment of the present disclosure. Figure 2 is Figure 1 a schematic diagram of the voltage and current timing of the hybrid flyback circuit shown in. The hybrid flyback circuit 1 of the present embodiment receives an input voltage V in at the input terminal, and the hybrid flyback circuit 1 converts the input voltage V in into an output voltage V o , and outputs the output voltage V o at the output terminal of the hybrid flyback circuit 1. In addition, the hybrid flyback circuit 1 includes a half-bridge switch circuit 2, a transformer T r , a resonant circuit 3, a current sampling circuit 4, a rectifier circuit 5, and a control unit 6.

[0057] The half-bridge switch circuit 2 is electrically connected to the input terminal of the hybrid flyback circuit 1 to receive the input voltage V in , and includes an upper-arm switch S1 and a lower-arm switch S2. The upper-arm switch S1 and the lower-arm switch S2 are connected in series and electrically connected to the midpoint. The transformer T r includes a primary winding N p and a secondary winding N s , and the turns ratio of the primary winding N p to the secondary winding N s is N:1, where N is a positive number.

[0058] The resonant circuit 3 is connected in series with the primary winding N p , and is electrically connected to the half-bridge switch circuit 2. In some embodiments, as Figure 1 shown, the resonant circuit 3 is electrically connected to the midpoint between the upper-arm switch S1 and the lower-arm switch S2.

[0059] In some embodiments, the resonant circuit 3 may include a resonant capacitor C r and a resonant inductor L r . The resonant capacitor C r is connected in series with the resonant inductor L r between the half-bridge switch circuit 2 and the primary winding N p .

[0060] The current sampling circuit 4 is used to sample the primary current of the transformer T r , and outputs a current sampling signal ILr 。In some embodiments, the current sampling circuit 4 may be, but is not limited to, composed of a resistor, a Hall sensor, etc. In addition, the primary side current of the transformer T r may refer to the current flowing through the resonant capacitor C r and the resonant inductor L r . Therefore, the electrical connection position of the current sampling circuit 4 can be as Figure 1 shown, electrically connected to the negative pole of the half-bridge switching circuit 2, the excitation inductor L m and the primary winding N p , but not limited thereto, and there may be other implementation manners. For example, the current sampling circuit 4 may also be arranged at the midpoint between, for example, the upper-arm switch S1 and the lower-arm switch S2 and the resonant capacitor C r .

[0061] The rectifier circuit 5 is electrically connected to the secondary winding N r of the transformer T s and the output terminal of the flyback hybrid circuit 1 for rectification operation. In some embodiments, the rectifier circuit 5 includes at least one rectifier switch S R and an output capacitor C o . The rectifier switch S R is electrically connected to the secondary winding N r of the transformer T s . The output capacitor C o is electrically connected to the rectifier switch S R and the output terminal of the flyback hybrid circuit 1.

[0062] The control unit 6 is electrically connected to the half-bridge switching circuit 2 and the current sampling circuit 4. The control unit 6 is used to output different control signals to control the operation of the upper-arm switch S1 and the lower-arm switch S2 of the half-bridge switching circuit 2 respectively, so that the upper-arm switch S1 and the lower-arm switch S2 are complementarily turned on, and includes an output voltage feedback unit 60, a peak current comparison unit 61, a first dead-time delay unit 62, a negative peak current feedback unit 63, a conduction control unit 64 and a second dead-time delay unit 65.

[0063] The output voltage feedback unit 60 is electrically connected to the output terminal of the flyback hybrid circuit 1 and is used to generate a first voltage feedback signal V o_ref according to the reference voltage V o and the output voltage V FB output by the flyback hybrid circuit 1. The peak current comparison unit 61 is electrically connected to the output voltage feedback unit 60 and the current sampling circuit 4 and is used to compare the current sampling signal I Lr with the first voltage feedback signal V FB , and when the current sampling signal I Lr is equal to the first voltage feedback signal V FB , generate a turn-off control signal S 1off, the driving control unit 6 controls the upper-arm switch S1 to turn off.

[0064] The first dead-time delay unit 62 is electrically connected to the peak current comparison unit 61, and is used to generate a turn-on control signal S after the upper-arm switch S1 turns off and after a first dead time. 2on , the driving control unit 6 controls the lower-arm switch S2 to turn on. In some embodiments, the turn-off control signal S output by the peak current comparison unit 61 1off is provided to the first dead-time delay unit 62, so that the first dead-time delay unit 62 generates a turn-on control signal S after the upper-arm switch S1 turns off and after a first dead time. 2on , the driving control unit 6 controls the lower-arm switch S2 to turn on.

[0065] The negative peak current feedback unit 63 is used to obtain the negative peak current value of the primary-side current according to the current sampling signal I Lr , and generate a second voltage feedback signal V according to the negative peak current value and the reference current I neg_ref . The conduction control unit 64 is electrically connected to the negative peak current feedback unit 63, and is used to control the on-time length of the lower-arm switch S2 according to the second voltage feedback signal V Ineg , and generate a turn-off control signal S Ineg , so that the driving control unit 6 controls the lower-arm switch S2 to turn off. The second dead-time delay unit 65 is electrically connected to the conduction control unit 64, and is used to generate a turn-on control signal S after the lower-arm switch S2 turns off and after a second dead time. 2off , so that the driving control unit 6 controls the upper-arm switch S1 to turn on. In some embodiments, the turn-off control signal S output by the conduction control unit 64 1on is provided to the second dead-time delay unit 65, so that the second dead-time delay unit 65 generates a turn-on control signal S after the lower-arm switch S2 turns off and after a second dead time. 2off , so that the driving control unit 6 controls the upper-arm switch S1 to turn on. In addition, in this embodiment, the turn-on control signal S 1on is, for example, a high level, and the turn-off control signal S 1on is, for example, a low level, and the control signal received by the upper-arm switch S1 control unit is composed of the turn-on control signal S 1off and the turn-off control signal S 1on . The turn-on control signal S 1off is, for example, a high level, and the turn-off control signal S 2on is, for example, a low level, and the control signal received by the lower-arm switch S2 control unit is composed of the turn-on control signal S 2off and the turn-off control signal S 2on . 2off

[0066] As can be seen from the above, compared with the adaptive adjustment control method of the traditional flyback circuit, after the lower-arm switch S2 of the half-bridge switch circuit 2 is turned on under zero voltage in the flyback circuit 1 of the present disclosure, the length of the time for turning on the lower-arm switch S2 is controlled in a feedback control manner, and then the lower-arm switch S2 is turned off. In this way, due to the adoption of feedback control, the response speed of the feedback loop is set by adjusting the parameters of the feedback loop, and ideally, the crossover frequency can reach half of the switching frequency. Therefore, the adjustment speed of the negative peak value of the magnetizing current can fully meet the requirements of the output dynamics of the flyback circuit 1 of the present disclosure. At the same time, due to the adoption of feedback control in the flyback circuit 1 of the present disclosure, the negative peak value of the magnetizing current will be locked near the set ideal value, resulting in better steady-state efficiency of the flyback circuit 1 of the present disclosure.

[0067] In the above embodiment, the reference current I neg_ref satisfies the following formula (1):

[0068]

[0069] wherein, Lm is the inductance value of the magnetizing inductor Lm of the resonant circuit 3, I neg_ref is the reference current, C oss1 is the capacitance value of the first parasitic capacitor C oss1 of the upper-arm switch S1, C oss2 is the capacitance value of the second parasitic capacitor C oss2 of the lower-arm switch S2, V in is the input voltage V in received by the flyback circuit 1.

[0070] In addition, in some embodiments, the negative peak current value obtained by the negative peak current feedback unit 63 is equal to the negative peak current value of the primary current after the lower-arm switch S2 is disconnected for a second set time in the previous switching cycle.

[0071] Please refer to Figure 2 , and in cooperation with Figure 1 , Figure 2 is Figure 1 the waveform timing diagram of the control signal received by the lower-arm switch, the resonant current flowing through the resonant inductor, and the magnetizing current flowing through the magnetizing inductor shown. In some embodiments, as Figure 1 shown, the control unit 6 further includes a current holding unit 66. The current holding unit 66 is used to detect the turn-off moment of the lower-arm switch S2. For example, according to the falling edge of the control signal (i.e., the turn-on control signal S 2on ) provided by the control unit 6 to the lower-arm switch S2, the turn-off moment of the lower-arm switch S2 is detected, and after the lower-arm switch S2 is turned off and after a second set time, the negative peak current value of the primary current is obtained according to the current sampling signal I Lr , that is, asFigure 2 As shown, when the falling edge of the turn-on control signal S is detected and after the second set time T has elapsed, the current holding unit 66 obtains the negative peak current value of the primary side current based on the current sampling signal I 2on At this time, the obtained primary side current is the required negative peak current value, and the current holding unit 66 holds this negative peak current value until the next cycle for calculation. In some embodiments, the second set time is less than or equal to 200 ns. In addition, in Lr Figure 2 Figure 2 Figure 2 Lr i is the current flowing through the resonant inductor L r i Lm is the current flowing through the resonant inductor L m

[0072] In addition, in other embodiments, the output voltage V of the flyback hybrid circuit 1 is variable, and the output voltage V o For example, is 5V, 9V, 15V or 20V, but is not limited thereto. o

[0073] Please refer to Figure 3 which shows the detailed circuit structure diagram of the turn-on control unit of the flyback hybrid circuit shown in Figure 1 Figure 1 2on 2on Ineg Ineg Ineg Ineg 2off 2off

[0074] In other embodiments, the turn-on timing unit 641 can be changed to detect the turn-on moment of the lower arm switch S2, and time the length of the turn-on time of the lower arm switch S2, and output the timing result. The turn-on comparison unit 640 is also changed to be based on the second voltage feedback signal V Ineg ​​Set a first set time length, and the conduction comparison unit 640 further confirms whether the time length of the turn-on of the lower-arm switch S2 is equal to the first set time length according to the output timing result output by the conduction timing unit 641. When the time length of the turn-on of the lower-arm switch S2 is equal to the first set time length, the conduction comparison unit 640 generates a turn-off control signal S 2off , so as to drive the control unit 6 to turn off the lower-arm switch S2.

[0075] Please refer to Figure 4 and cooperate with Figure 1 , where Figure 4 is the schematic flow chart of the steps of the control method of the flyback converter circuit applied to the preferred embodiment of the present disclosure Figure 1 shown in. The control method of this embodiment can be applied to, for example, Figure 1 the control unit 6 of the flyback converter circuit 1 shown in. The control method includes the following steps.

[0076] Step S1, the output voltage feedback unit 60 samples the output voltage V output by the flyback converter circuit 1 o , and generates a first voltage feedback signal V according to the reference voltage V o_ref and the output voltage V o . FB。

[0077] Step S2, the current sampling circuit 4 samples the primary current of the transformer Tr and outputs a current sampling signal I Lr .

[0078] Step S3, the peak current comparison unit 61 of the control unit 6 compares the current sampling signal I Lr and the first voltage feedback signal V FB . When the current sampling signal I Lr is equal to the first voltage feedback signal V FB , the peak current comparison unit 61 drives the control unit 6 to control the upper-arm switch S1 to turn off.

[0079] Step S4, the first dead-time delay unit 62 of the control unit 6 drives the control unit 6 to control the lower-arm switch S2 to turn on after the upper-arm switch S1 turns off and passes through the first dead-time.

[0080] Step S5, the negative peak current feedback unit 63 of the control unit 6 obtains the negative peak current value of the primary current according to the current sampling signal I Lr , and generates a second voltage feedback signal V according to the negative peak current value and the reference current I neg_ref . Ineg。

[0081] Step S6: The conduction control unit 64 of the control unit 6 controls the conduction time length of the lower-arm switch S2 according to the second voltage feedback signal, and drives the control unit 6 to turn off the lower-arm switch S2.

[0082] Step S7: The second dead-time delay unit 65 of the control unit 6 drives the control unit 6 to turn on the upper-arm switch S1 after the lower-arm switch S2 is turned off and after a second dead time.

[0083] It should be noted that the sequence of Step S1 and Step S2 is not limited. That is, the output voltage can be sampled first and then the primary current can be sampled, or the primary current can be sampled first and then the output voltage can be sampled. Even in some embodiments, the output voltage and the primary current can be sampled simultaneously.

[0084] In some embodiments, Step S6 may further include a first sub-step and a second sub-step. The first sub-step is that the conduction timing unit 641 of the conduction control unit 64 detects the conduction moment of the lower-arm switch S2 to generate a voltage signal reflecting the conduction time length of the lower-arm switch S2. The second sub-step is that the conduction comparison unit 640 of the conduction control unit 64 compares the voltage signal with the second voltage feedback signal V Ineg and when the voltage signal is equal to the second voltage feedback signal V Ineg , the conduction comparison unit 640 generates a turn-off control signal S 2off to drive the control unit 6 to turn off the lower-arm switch S2.

[0085] In other embodiments, Step S6 is not limited to including the above first sub-step and second sub-step, but instead includes a third sub-step and a fourth sub-step. The third sub-step is that the conduction timing unit 641 of the conduction control unit 64 detects the conduction moment of the lower-arm switch S2, and measures the conduction time length of the lower-arm switch S2 and outputs a measurement result. The fourth sub-step is that the conduction comparison unit 640 of the conduction control unit 64 sets a first set time length according to the second voltage feedback signal V Ineg and when the measurement result is equal to the first set time length, the conduction comparison unit 640 generates a turn-off control signal S 2off to drive the control unit 6 to turn off the lower-arm switch S2.

[0086] In summary, the present disclosure provides a hybrid flyback circuit and a control method. After turning on the lower-arm switch of the half-bridge switching circuit under zero voltage, the hybrid flyback circuit and the control method of the present disclosure control the on-time length of the lower-arm switch in a feedback control manner, and then turn off the lower-arm switch. In this way, due to the adoption of feedback control, the response speed of the feedback loop is set by adjusting the parameters of the feedback loop, and ideally, the crossover frequency can reach half of the switching frequency. Therefore, the adjustment speed of the negative peak value of the magnetizing current can fully meet the requirements of the output dynamics of the hybrid flyback circuit 1. At the same time, since the hybrid flyback circuit 1 of the present disclosure adopts feedback control, the negative peak value of the magnetizing current will be locked near the set ideal value, resulting in better steady-state efficiency of the hybrid flyback circuit of the present disclosure.

Claims

1. A hybrid flyback circuit, comprising: A half-bridge switching circuit, including an upper-arm switch and a lower-arm switch; A transformer, including a primary winding and a secondary winding; A resonant circuit, serially electrically connected to the primary winding; A current sampling circuit, configured to sample a primary current of the transformer and output a current sampling signal; A rectifying circuit is electrically connected to the secondary winding; And A control unit, configured to control the operation of the half-bridge switching circuit, and including: An output voltage feedback unit, configured to generate a first voltage feedback signal according to a reference voltage and an output voltage output by the hybrid flyback circuit; A peak current comparison unit, configured to compare the current sampling signal with the first voltage feedback signal, and drive the control unit to control the turn-off of the upper-arm switch when the current sampling signal is equal to the first voltage feedback signal; A first dead-time delay unit, configured to drive the control unit to control the turn-on of the lower-arm switch after the upper-arm switch is turned off and after a first dead-time; A negative peak current feedback unit, configured to obtain a negative peak current value of the primary current according to the current sampling signal, and generate a second voltage feedback signal according to the negative peak current value and a reference current; A conduction control unit, configured to control the conduction time length of the lower-arm switch according to the second voltage feedback signal, and drive the control unit to control the turn-off of the lower-arm switch; And A second dead-time delay unit, configured to drive the control unit to control the turn-on of the upper-arm switch after the lower-arm switch is turned off and after a second dead-time.

2. The flyback hybrid circuit according to claim 1, wherein, The conduction control unit includes: A conduction timing unit, detecting the turn-on moment of the lower-arm switch to generate a voltage signal reflecting the conduction time length of the lower-arm switch; A conduction comparison unit, comparing the voltage signal with the second voltage feedback signal, and when the second voltage feedback signal is equal to the voltage signal, driving the control unit to control the turn-off of the lower-arm switch.

3. The flyback hybrid circuit according to claim 1, wherein, The conduction control unit includes: A conduction timing unit, detecting the turn-on moment of the lower-arm switch, timing the conduction time length of the lower-arm switch, and outputting a timing result; A conduction comparison unit, configured to set a first set time length according to the second voltage feedback signal, and driving the control unit to control the turn-off of the lower-arm switch when the timing result is equal to the first set time length.

4. The hybrid flyback circuit according to claim 1, wherein the control unit further includes a current holding unit, configured to detect the turn-off moment of the lower-arm switch, and after the lower-arm switch is turned off and after a second set time, obtaining the negative peak current value of the primary current according to the current sampling signal.

5. The flyback hybrid circuit according to claim 4, wherein, The second set time is less than or equal to 200 ns.

6. The hybrid flyback circuit according to claim 1, wherein the reference current satisfies: where Lm is an inductance value of an excitation inductor of the resonant circuit, I neg_ref is the reference current, C oss1 is a capacitance value of a first parasitic capacitance of the upper-arm switch, C oss2 is a capacitance value of a second parasitic capacitance of the lower-arm switch, V in is an input voltage received by the flyback hybrid circuit.

7. The hybrid flyback circuit according to claim 1, the negative peak current value obtained by the negative peak current feedback unit is equal to the primary current after the lower-arm switch is turned off for a second set time in the previous switching cycle.

8. The flyback hybrid circuit as claimed in claim 7, wherein the second set time is set to be less than or equal to 200 ns.

9. A control method applied to a flyback hybrid circuit, wherein the flyback hybrid circuit further comprises a half-bridge switching circuit, a transformer, a resonant circuit, and a current sampling circuit. The half-bridge switching circuit comprises an upper-arm switch and a lower-arm switch. The transformer comprises a primary winding and a secondary winding. The resonant circuit is serially electrically connected to the primary winding. The control method comprises the following steps: (S1) Sampling an output voltage output by the flyback hybrid circuit, and generating a first voltage feedback signal according to a reference voltage and the output voltage; (S2) Sampling a primary current of the transformer, and outputting a current sampling signal; (S3) Comparing the current sampling signal with the first voltage feedback signal, and when the current sampling signal is equal to the first voltage feedback signal, controlling the upper-arm switch to turn off; (S4) After the upper-arm switch is turned off and after a first dead time, controlling the lower-arm switch to turn on; (S5) Obtaining a negative peak current value of the primary current according to the current sampling signal, and generating a second voltage feedback signal according to the negative peak current value and a reference current; (S6) Controlling a turn-on time length of the lower-arm switch according to the second voltage feedback signal, and controlling the lower-arm switch to turn off; and (S7) After the lower-arm switch is turned off and after a second dead time, controlling the upper-arm switch to turn on.

10. The control method according to claim 9, wherein, Step (S6) further comprises: detecting a turn-on moment of the lower-arm switch to generate a voltage signal reflecting the turn-on time length of the lower-arm switch; and comparing the voltage signal with the second voltage feedback signal, and when the voltage signal is equal to the second voltage feedback signal, controlling the lower-arm switch to turn off.

11. The control method according to claim 9, wherein, Step (S6) further comprises: detecting a turn-on moment of the lower-arm switch, timing the turn-on time length of the lower-arm switch, and outputting a timing result; and setting a first set time length according to the second voltage feedback signal, and when the timing result is equal to the first set time length, controlling the lower-arm switch to turn off.

12. The control method as claimed in claim 9, wherein in step (S5), the negative peak current value obtained by the current sampling signal is the primary current after the lower-arm switch is turned off for a second set time in a previous switching cycle.

13. The control method as claimed in claim 12, wherein the second set time is set to be less than or equal to 200 ns.

14. The control method as claimed in claim 9, wherein the reference current satisfies: where Lm is the inductance value of an excitation inductor of the resonant circuit, I neg is the reference current, C oss1 is the capacitance value of a first parasitic capacitor of the upper-arm switch, C oss2 is the capacitance value of a second parasitic capacitor of the lower-arm switch, V bus is an input voltage received by the flyback converter circuit.

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