Flyback converter circuit, control method, converter, servo motor and driver

Abstract

The application discloses a flyback conversion circuit, a control method, a converter, a servo motor and a driver thereof. One end of a first switch is connected with a bus, and the other end is connected with a second end of a primary coil of a transformer. One end of a second switch is connected with a first end of the primary coil, and the other end is grounded. A first diode is connected in series with a third switch between the bus and the first end of the primary coil. The third switch is connected in parallel with a first absorption circuit. A second diode is connected in series with a fourth switch between the second end of the primary coil and the ground. The fourth switch is connected in parallel with a second absorption circuit. When a bus sampling voltage is greater than a threshold voltage, a voltage comparison circuit controls the third switch and the fourth switch to be turned on, so as to form a first clamping circuit and a second clamping circuit of the primary coil. When the bus sampling voltage is less than the threshold voltage, the voltage comparison circuit controls the third switch and the fourth switch to be turned off, so as to form a first clamping absorption circuit and a second clamping absorption circuit of the primary coil.

Description

Technical Field

[0001] This invention relates to the field of DC-DC converters, and more particularly to a flyback converter circuit, control method, converter, servo motor, and driver thereof. Background Technology

[0002] Based on the number of switches connected in series with the primary coil and the connection structure, flyback converters can be classified into two-tube flyback converters and single-tube flyback converters.

[0003] Figure 1 This is a circuit diagram of a two-transistor flyback converter in the prior art. Because the freewheeling current of the primary winding (caused by the induced electromotive force generated by the leakage inductance of the primary winding, etc.) can be returned to the bus through clamping diodes D1 and D2, the switching transistors Q1 and Q2 only need to withstand a voltage approximately equal to the bus voltage Vin. Therefore, this two-transistor flyback converter is more easily applied to high input voltage situations. However, under low input voltage conditions, i.e., when the bus voltage is lower than the voltage reflected from the secondary winding to the primary winding, the clamping diodes will return the energy that should have been transferred to the secondary winding to the primary winding through a forward converter. Thus, the secondary winding can only output an output voltage slightly lower than the turns ratio of the bus voltage. That is, if the turns ratio of the primary and secondary windings of the transformer is n:1, then the secondary output voltage is: Vo = Vin / n - VD (Vo, Vin, and VD are the output voltage, the bus input voltage, and the voltage drop of the rectifier diode D, respectively).

[0004] Figure 2 This is a circuit diagram of a current-generation single-transistor flyback converter. Because the switches Q1 and Q2, connected in series with the primary winding, need to withstand the combined voltage of the bus voltage, the voltage reflected from the secondary winding to the primary winding through the transformer (i.e., the reflected voltage), and the voltage spike generated when switches Q1 and Q2 are turned off (the induced electromotive force generated by the leakage inductance of the primary winding), the voltage that switches Q1 and Q2 need to withstand is much greater under high input voltage conditions. This significantly limits the maximum input voltage of the single-transistor flyback converter. However, theoretically, with proper design, this circuit can still output normally under extremely low input voltage conditions.

[0005] Existing two-transistor flyback converters exhibit the aforementioned problems at low input voltages. Designers of these converters can only avoid this voltage range and determine the lowest possible input voltage, unable to accommodate both the lowest and highest input voltages across a wide input range. In summary, single-transistor flyback converters offer no advantage at high input voltages, while two-transistor flyback converters suffer from problems at low input voltages.

[0006] For example, supercapacitors are now widely used as backup power sources for servo drives, such as for backup voltage in wind turbine pitch servo drives. When AC power is supplied from the grid, a 400Vac three-phase AC input to the AC rectifier circuit can produce a DC voltage of up to 800Vdc on the bus under extreme conditions. In the event of a grid outage, the backup supercapacitor begins to operate. To maximize the utilization of the supercapacitor's energy, its voltage needs to be released as low as possible (ideally to zero). It can be seen that the operating voltage range of the bus voltage is between tens of volts and 800Vdc, and existing dual-tube and single-tube flyback converters struggle to operate within this range. Summary of the Invention

[0007] Based on the above situation, the main objective of this invention is to provide a flyback converter circuit, control method, converter, servo motor and driver, which can operate normally over a wide range of input voltages, and the withstand voltage values ​​of the first and second switches can be relatively low.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0009] A flyback converter circuit includes a first switch, a second switch, a first diode, and a second diode, and further includes: a third switch, a fourth switch, a voltage comparator circuit, a first absorption circuit, and a second absorption circuit. The first absorption circuit includes a first absorption capacitor and a first absorption resistor, and the second absorption circuit includes a second absorption capacitor and a second absorption resistor. One end of the first switch is connected to a bus, and the other end is connected to the second end of the primary winding of the transformer. One end of the second switch is connected to the first end of the primary winding, and the other end is grounded. The first diode and the third switch are connected in series between the bus and the first end of the primary winding. The third switch is connected in parallel with the first absorption circuit, in which the first absorption capacitor and the first absorption resistor are connected in parallel. The second diode and the fourth switch are connected in series between the second end of the primary winding and ground. The fourth switch is connected in parallel with the second absorption circuit, in which the second absorption capacitor and the second absorption resistor are connected in parallel. The voltage comparator circuit compares the bus sampled voltage with a threshold voltage. When the bus sampled voltage is greater than the threshold voltage, the voltage comparator circuit... The voltage comparator circuit controls the third switch to be turned on, thereby forming a first clamping circuit for the primary coil with the first diode and the third switch. The current direction in the first clamping circuit is from the first end of the primary coil, the anode of the first diode, to the cathode of the first diode, and the third switch short-circuits the first absorption circuit. The voltage comparator circuit also controls the fourth switch to be turned on, thereby forming a second clamping circuit for the primary coil with the second diode and the fourth switch. The current direction in the second clamping circuit is from the anode of the second diode, the cathode of the second diode, to the second end of the primary coil, and the fourth switch short-circuits the second absorption circuit. When the bus sampling voltage is less than the threshold voltage: the voltage comparator circuit controls the third switch to be turned off, thereby forming a first clamping absorption circuit for the primary coil with the first diode and the first absorption circuit. The voltage comparator circuit also controls the fourth switch to be turned off, thereby forming a second clamping absorption circuit for the primary coil with the second diode and the second absorption circuit.

[0010] Preferably, the flyback converter circuit further includes a third diode and a fourth diode. The first absorption circuit is connected in series with the third diode and then in parallel with the third switch. When the third switch is turned on, the third diode is used to prevent the charge of the first absorption capacitor from discharging through the third switch. After the third switch is turned off, the third diode constitutes a component of the first absorption clamping circuit. The second absorption circuit is connected in series with the fourth diode and then in parallel with the fourth switch. When the fourth switch is turned on, the fourth diode is used to prevent the charge of the second absorption capacitor from discharging through the fourth switch. After the fourth switch is turned off, the fourth diode constitutes a component of the second absorption clamping circuit.

[0011] Preferably, the flyback converter circuit further includes a control unit, wherein the secondary winding of the transformer outputs the output voltage through a rectifier diode; the control unit is configured to: when the output voltage of the flyback converter circuit is adjusted to a new voltage value, update the threshold voltage according to the following relationship between the threshold voltage and the output voltage: Vth=k*n*(Vo+Vd); where Vth, Vo, and Vd are respectively: the threshold voltage, the output voltage, and the voltage drop of the rectifier diode, n is the turns ratio of the primary winding and the secondary winding of the transformer, and k is a sampling coefficient with a value range of (0, 1); and output the updated threshold voltage to the voltage comparison circuit.

[0012] Preferably, the flyback converter circuit further includes a control unit, wherein the secondary winding of the transformer outputs the output voltage through a rectifier diode; the control unit is configured to: when the output voltage of the flyback converter circuit is adjusted to a new voltage value, update the threshold voltage according to the following relationship between the threshold voltage and the output voltage: Vth=k*(n*(Vo+Vd)+V1); where Vth, Vo, and Vd are respectively: the threshold voltage, the output voltage, and the voltage drop of the rectifier diode, V1 is a constant between 5V and 10V, n is the turns ratio of the primary winding and the secondary winding of the transformer, and k is a sampling coefficient with a value range of (0, 1); and output the updated threshold voltage to the voltage comparison circuit.

[0013] This invention also provides a control method for a flyback converter circuit. Using the aforementioned flyback converter circuit, the control method includes the following steps: the voltage comparator circuit compares the bus sampled voltage with a threshold voltage. When the bus sampled voltage is greater than the threshold voltage: the voltage comparator circuit controls the third switch to conduct, thereby causing the first diode and the third switch to form a first clamping circuit for the primary coil. The current direction in the first clamping circuit is from the first end of the primary coil, the anode of the first diode, to the cathode of the first diode, and the third switch short-circuits the first absorption circuit; the voltage comparator circuit also controls the fourth switch to conduct, from... The second diode and the fourth switch form a second clamping circuit for the primary coil. The current direction in the second clamping circuit is from the anode and cathode of the second diode to the second end of the primary coil, and the fourth switch short-circuits the second absorption circuit. When the bus sampling voltage is less than the threshold voltage: the voltage comparator circuit controls the third switch to open, so that the first diode and the first absorption circuit form a first clamping absorption circuit for the primary coil. The voltage comparator circuit also controls the fourth switch to open, so that the second diode and the second absorption circuit form a second clamping absorption circuit for the primary coil.

[0014] Preferably, the flyback converter circuit further includes a control unit, and the secondary coil of the transformer outputs the output voltage through a rectifier diode; the control method further includes the following steps: when the output voltage of the flyback converter circuit is adjusted to a new voltage value, the control unit updates the threshold voltage according to the following relationship between the threshold voltage and the output voltage: Vth=k*n*(Vo+Vd); where Vth, Vo and Vd are respectively: the threshold voltage, the output voltage and the voltage drop of the rectifier diode, n is the turns ratio of the primary coil and the secondary coil of the transformer, and k is a sampling coefficient with a value range of (0, 1); the control unit outputs the updated threshold voltage to the voltage comparison circuit.

[0015] Preferably, the flyback converter circuit further includes a control unit, and the secondary coil of the transformer outputs the output voltage through a rectifier diode; the control method further includes the following steps: when the output voltage of the flyback converter circuit is adjusted to a new voltage value, the control unit updates the threshold voltage according to the following relationship between the threshold voltage and the output voltage: Vth=k*(n*(Vo+Vd)+V1); where Vth, Vo and Vd are respectively: the threshold voltage, the output voltage and the voltage drop of the rectifier diode, V1 is a constant between 5V and 10V, n is the turns ratio of the primary coil and the secondary coil of the transformer, and k is a sampling coefficient with a value range of (0, 1); the control unit outputs the updated threshold voltage to the voltage comparison circuit.

[0016] The present invention also provides a flyback converter, including a transformer, and further including any of the flyback converter circuits described above.

[0017] The present invention also provides a servo motor driver, including a transformer and any of the flyback converter circuits described above.

[0018] The present invention also provides a servo motor, including the aforementioned servo motor driver.

[0019] [Beneficial Effects]

[0020] When the bus sampling voltage is greater than the threshold voltage, the voltage comparator circuit controls the third and fourth switches to be turned on, thereby forming a first clamping circuit for the primary coil with the first diode and the third switch, and a second clamping circuit for the primary coil with the second diode and the fourth switch. This is similar to a two-transistor flyback converter, where the withstand voltage values ​​of the first and second switches can be lower. When the bus sampling voltage is less than the threshold voltage, the voltage comparator circuit controls the third and fourth switches to be turned off, thereby forming a first clamping absorption circuit for the primary coil with the first diode and the first absorption circuit, and a second clamping absorption circuit for the primary coil with the second diode and the second absorption circuit. The first and second ends of the transformer primary coil will not be clamped, thus avoiding the problem that "the energy of the secondary coil is fed back to the primary coil through a forward converter, resulting in the secondary coil only receiving an output voltage with a turns ratio slightly lower than the bus voltage." Therefore, this flyback converter circuit can operate normally over a wide range of input voltages, and the withstand voltage values ​​of the first and second switches can be lower.

[0021] Other beneficial effects of the present invention will be explained in detail through the introduction of specific technical features and technical solutions in specific embodiments. Those skilled in the art should be able to understand the beneficial technical effects brought about by these technical features and technical solutions through the introduction of these technical features and technical solutions. Attached Figure Description

[0022] The preferred embodiment of the flyback converter circuit of the present invention will now be described with reference to the accompanying drawings. In the drawings:

[0023] Figure 1 This is a schematic diagram of the circuit topology of a dual-transistor flyback converter circuit in the prior art;

[0024] Figure 2 This is a schematic diagram of the circuit topology of a single-transistor flyback converter circuit in the prior art;

[0025] Figure 3 This is a flyback converter circuit according to a preferred embodiment of the present invention;

[0026] Figure 4 This is a flyback converter circuit according to another preferred embodiment of the present invention;

[0027] Figure 5 This is a flyback converter circuit according to another preferred embodiment of the present invention;

[0028] Figure 6 This is a flyback converter circuit according to another preferred embodiment of the present invention;

[0029] Figure 7 This is a flyback converter circuit according to another preferred embodiment of the present invention;

[0030] Figure 8 This is a flyback converter circuit according to another preferred embodiment of the present invention. Detailed Implementation

[0031] The present invention is described below based on embodiments, but the present invention is not limited to these embodiments. In the following detailed description of the present invention, some specific details are described in detail, but well-known methods, processes, procedures, and elements are not described in detail in order to avoid obscuring the essence of the present invention.

[0032] Furthermore, those skilled in the art should understand that the accompanying drawings provided herein are for illustrative purposes only and are not necessarily drawn to scale.

[0033] Unless the context explicitly requires it, the words "comprising," "including," and similar terms throughout the specification and claims should be interpreted as encompassing rather than being exclusive or exhaustive; that is, meaning "including but not limited to."

[0034] In the description of this invention, it should be understood that the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance. Furthermore, in the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0035] This flyback converter circuit is well-suited for applications with a wide range of input voltage variations. Products that utilize this flyback converter circuit include: switching power supplies, frequency converters, servo drives, UPS, inverters, energy storage devices, etc. Figure 3 This is a flyback converter circuit according to one embodiment of the present invention. The flyback converter circuit is used to convert the voltage on its bus into an output voltage Vo to provide to the load, such as a servo motor (correspondingly, this flyback converter circuit is a component of a servo driver).

[0036] The flyback converter circuit includes a control unit (not shown in the figure), a drive unit (not shown in the figure), a bus capacitor C1, a first switch Q1, a second switch Q2, a first diode D1 (freewheeling diode), a second diode D2 (freewheeling diode), a third switch Q3, a fourth switch Q4, a voltage comparator circuit, a first absorption circuit, a second absorption circuit, a transformer T, a rectifier diode D, and an output filter capacitor C2. The first absorption circuit includes a first absorption capacitor C3 and a first absorption resistor R1, and the second absorption circuit includes a second absorption capacitor C4 and a second absorption resistor R2. The first switch Q1, the second switch Q2, the third switch Q3, and the fourth switch Q4 can be MOSFETs, such as N-channel MOSFETs or P-channel MOSFETs, and IGBTs (Insulated Gate Bipolar Transistors).

[0037] The flyback converter circuit's bus is grounded through bus capacitor C1. The voltage on the bus comes from the output voltage of the preceding stage circuit, which is also the input voltage of the flyback converter circuit. The output voltage of this preceding stage circuit varies considerably, for example, from 20V to 800V. The preceding stage circuit can be a supercapacitor (i.e., a backup power supply) and an AC rectifier circuit, operating under corresponding conditions. When the mains power is available, the AC rectifier circuit operates, converting the AC voltage to DC voltage to supply the bus; when the mains power is depleted, the supercapacitor operates, and its output DC voltage is supplied to the bus.

[0038] The first switch Q1 is connected to the busbar at one end and to the second terminal T2 of the primary coil of the transformer T at the other end; the second switch Q2 is connected to the first terminal T1 of the primary coil at one end and to ground at the other end.

[0039] The first diode D1 and the third switch Q3 are connected in series between the busbar and the first terminal T1 of the primary coil. For example... Figure 3As shown, in one embodiment, the third switch Q3 is connected in series between the first terminal T1 of the primary coil and the anode of the first diode D1; in another embodiment, as... Figure 4 As shown, the third switch Q3 is connected in series between the busbar and the cathode of the first diode D1. The third switch Q3 is connected in parallel with the first absorption circuit, in which the first absorption capacitor C3 and the first absorption resistor R1 are connected in parallel.

[0040] The second diode D2 and the fourth switch Q4 are connected in series between the second terminal T2 of the primary coil and ground. For example... Figure 3 As shown, in one embodiment, the fourth switch Q4 is connected in series between the anode of the second diode D2 and ground. In another embodiment, as... Figure 6 As shown, the fourth switch Q4 is connected in series between the second terminal T2 of the primary coil and the cathode of the second diode D2. The fourth switch Q4 is connected in parallel with the second absorption circuit, in which the second absorption capacitor C4 and the second absorption resistor R2 are connected in parallel.

[0041] The voltage comparator circuit compares the bus sampling voltage (i.e., the sampling voltage of the input voltage) with the threshold voltage. When the bus sampling voltage is greater than the threshold voltage, the voltage comparator circuit controls the third switch Q3 to turn on and the fourth switch Q4 to turn on. This causes the first diode D1 and the third switch Q3 to form the first clamping circuit of the primary coil, and the second diode D2 and the fourth switch Q4 to form the second clamping circuit of the primary coil. The current in the first clamping circuit (also called the follow current, which is the current generated when the first switch Q1 and the second switch Q2 are turned off during the switching cycle of the first switch Q1 and the second switch Q2) is directed from the first terminal T1 of the primary coil, the third switch Q3, and the anode of the first diode D1 to the cathode of the first diode D1, and causes the third switch Q3 to short-circuit the first absorption circuit. The current in the second clamping circuit is directed from the fourth switch Q4, the anode of the second diode D2, and the cathode of the second diode D2 to the second terminal T2 of the primary coil, and causes the fourth switch Q4 to short-circuit the second absorption circuit.

[0042] When the bus sampling voltage is less than the threshold voltage, the voltage comparator circuit controls the third switch Q3 to open and the fourth switch Q4 to open, thereby causing the first diode D1 and the first absorption circuit to form the first clamping absorption circuit of the primary coil, and the second diode D2 and the second absorption circuit to form the second clamping absorption circuit of the primary coil. Figure 3As shown, in one embodiment, the voltage comparison circuit employs a comparator. One end of the comparator receives the bus sampling voltage (i.e., the sampling voltage of the input voltage) V'in, and the other end receives the threshold voltage. The output terminal outputs a comparison result signal. For example, when the input voltage is greater than the threshold voltage, the comparison result signal is high; when it is less than the threshold voltage, the comparison result signal is low. In some embodiments, the flyback converter circuit further includes a drive circuit, which converts the comparison result signal into drive signals for the third switch Q3 and the fourth switch Q4. These signals are input to the control terminals of the third switch Q3 and the fourth switch Q4, respectively, to control the third switch Q3 and the fourth switch Q4 to turn on or off. For example, the third switch Q3 is a MOSFET. The drive signal is input to the gate of the MOSFET, and a resistor R3 is connected between the gate and the source. This provides both a bias voltage to the gate of the third switch Q3 and a fast release path for the accumulated charge on the gate. Similarly, the fourth switch Q4 is a MOSFET. The drive signal is input to the gate of the MOSFET. A resistor R4 is connected between the gate and the source, which can provide a bias voltage to the gate of the fourth switch Q4 and provide a fast release channel for the accumulated charge on the gate.

[0043] One end of the secondary winding of transformer T is connected to the positive output terminal Vo+ through rectifier diode D, and the other end is connected to the negative output terminal Vo-. The two ends of filter capacitor C2 are connected to the positive output terminal Vo+ and the negative output terminal Vo- respectively. The output voltage Vo between the positive output terminal Vo+ and the negative output terminal Vo- is provided to the load.

[0044] When the bus sampling voltage is greater than the threshold voltage, the voltage comparison circuit obtains the comparison result by comparing the bus sampling voltage with the threshold voltage, and then controls the third switch Q3 and the fourth switch Q4 to be turned on respectively. In this way, the third switch Q3 short-circuits the first absorption circuit, and the fourth switch Q4 short-circuits the second absorption circuit. The working process of the flyback converter circuit during the working cycle is described in detail below: (1) The control unit controls the first switch Q1 and the second switch Q2 to be turned on through the drive unit (not shown in the figure). The current flows out from the bus, passes through the first switch Q1, the primary coil and the second switch Q2 and flows into the ground. In this process, the current excites the transformer T, and the electrical energy is converted into magnetic energy. At this time, the rectifier diode D is cut off (i.e., turned off), and there is no current in the secondary coil. At this time, the voltage at the cathode of the second diode D2 is greater than the voltage at its anode, so the second diode D2 is cut off (i.e., turned off); the voltage at the cathode of the first diode D1 is greater than the voltage at its anode, so the first diode D1 is cut off (i.e., turned off); (2) After a certain period of time in step (1), the control unit controls the first switch Q1 and the second switch Q2 to open through the drive unit (not shown in the figure), the magnetic energy in the transformer T begins to be converted into electrical energy, the rectifier diode D is turned on, and there is current in the secondary coil; in addition, since the first switch Q1 and the second switch Q2 are opened instantaneously, the leakage inductance of the primary coil generates a large induced electromotive force; the output voltage Vo of the flyback converter circuit generates a reflected voltage in the primary coil due to the turns ratio of the transformer T (the turns ratio between the primary coil and the secondary coil), so the voltage difference across the primary coil is the sum of the induced electromotive force and the reflected voltage. Due to the clamping effect of the first diode D1, the voltage at the first terminal T1 of the primary coil is clamped at the sum of the input voltage and the voltage drop of the first diode D1 (i.e., Vin + VD1); due to the clamping effect of the second diode D2, the voltage at the second terminal T2 of the primary coil is clamped at the difference between 0 and the voltage drop of the second diode D2 (i.e., -VD2); thus, the freewheeling current in the primary coil flows out from the first terminal T1, flows through the first diode D1 into the bus, charges the bus capacitor C1, and the charging current returns to the second terminal T2 of the primary coil through the bus capacitor C1 and the second diode D2, forming a freewheeling current loop.

[0045] When the bus sampling voltage is less than the threshold voltage, the voltage comparison circuit obtains the comparison result by comparing the bus sampling voltage with the threshold voltage, and then controls the third switch Q3 and the fourth switch Q4 to open respectively, so that the first diode D1 and the first absorption circuit form the first clamping absorption circuit (RCD circuit) of the primary coil, and the second diode D2 and the second absorption circuit form the second clamping absorption circuit (RCD circuit) of the primary coil.

[0046] The following describes in detail the working process of the flyback converter circuit during its working cycle: (1) The control unit controls the first switch Q1 and the second switch Q2 to turn on through the drive unit (not shown in the figure). Current flows out from the bus, passes through the first switch Q1, the primary coil, and the second switch Q2, and flows into the ground. During this process, the current excites the transformer T, and electrical energy is converted into magnetic energy. At this time, the rectifier diode D is cut off (i.e., turned off), and there is no current in the secondary coil. At this time, the voltage of the cathode of the second diode D2 is greater than the voltage of its anode, so the second diode D2 is cut off (i.e., turned off); the voltage of the cathode of the first diode D1 is greater than the voltage of its anode, so the first diode D1 is cut off (i.e., turned off); (2) After a certain period of time in step (1), the control unit controls the first switch Q1 and the second switch Q2 to turn off through the drive unit (not shown in the figure). The magnetic energy in the transformer T begins to be converted into electrical energy, the rectifier diode D turns on, and there is current in the secondary coil; in addition, since the first switch Q1 and the second switch Q2 are turned off instantaneously, the leakage inductance of the primary coil generates a large induced electromotive force; the output current of the flyback converter circuit Due to the turns ratio of transformer T (the turns ratio between the primary and secondary coils), a reflected voltage is generated in the primary coil. That is, the voltage difference across the primary coil is the sum of the induced electromotive force and the reflected voltage. The first diode D1 and the second diode D2 are turned on, and the freewheeling current in the primary coil flows out from the first terminal T1. The first absorption capacitor C3 begins to charge. The charging current flows back to the bus after passing through the first absorption capacitor C3 and the first diode D1, and charges the bus capacitor C1. In addition, the second absorption capacitor C4 also begins to charge. The charging current flows out from the ground, and flows back to the second terminal T2 of the primary coil after passing through the second absorption capacitor C4 and the second diode D2.Due to the charging effect of the first absorption capacitor C3 and the second absorption capacitor C4, the voltage spikes caused by the induced electromotive force in the voltages of the first terminal T1 and the second terminal T2 of the primary coil are also absorbed and become smoother; (3) When the first absorption capacitor C3 is charged to a certain voltage (i.e., it stores a certain corresponding amount of electricity), the voltage difference between its low potential terminal P31 and the bus voltage is less than the forward voltage drop of the first diode D1, and the charging of the first absorption capacitor C3 is cut off (i.e., it is turned off). At this time, the second absorption capacitor C4 is charged to a certain voltage (i.e., it stores a certain corresponding amount of electricity), and the voltage difference between its high potential terminal P33 and the second terminal T2 of the primary coil is less than the forward voltage drop of the second diode D2, and the charging of the second absorption capacitor C4 is cut off (i.e., it is turned off). (4) The first absorption capacitor C3 can be discharged through the first absorption resistor R1. The discharge current flows out from the high potential terminal P32 of the first absorption capacitor C3 (the terminal connected to the first terminal T1 of the primary coil), and after passing through the first absorption resistor R1, it flows into the low potential terminal P31 of the first absorption capacitor C3 (the terminal that shares the same point as the anode of the first diode D1). Similarly, the second absorption capacitor C4 can be discharged through the second absorption resistor R2. The discharge current flows out from the high potential terminal P34 of the second absorption capacitor C4 (the terminal connected to ground), and after passing through the second absorption resistor R2, it flows into the low potential terminal P33 of the second absorption capacitor C4 (the terminal that shares the same point as the anode of the second diode D2). After discharging to a certain voltage value, the flyback converter circuit then... The next cycle begins with steps (1)-(3). In step (1) of this next cycle, the cathode voltage of the first diode D1 is the bus voltage, and its anode voltage is the voltage at the low potential terminal P31. At this time, the first diode D1 is cut off. The cathode voltage of the second diode D2 is the voltage at the second terminal T2 of the primary coil, and its anode voltage is the negative voltage at the low potential terminal P33. At this time, the second diode D2 is cut off. After step (3) of this next cycle, the first absorption capacitor C3 and the second absorption capacitor C4 start charging again. Therefore, when the bus sampling voltage is less than the threshold voltage, the voltage at the low potential terminal P31 of the first absorption capacitor C3 can be stably maintained during the operation of the flyback converter circuit. The voltage at the high potential terminal P32, VC3, is maintained above a certain voltage value (i.e., the first absorption capacitor C3 can store at least a certain amount of electrical energy). Similarly, the voltage at the high potential terminal P32, VC4, is maintained above a certain voltage value. This voltage value is related to the capacitance of the first absorption capacitor C3, the resistance of the first absorption resistor R1, and the duty cycle of the conduction time of the first switch Q1 and the second switch Q2. Likewise, the voltage at the low potential terminal P33, VC4, of the second absorption capacitor C4 is maintained below a certain voltage value (negative value) (i.e., at least a certain amount of electrical energy can be stored). This voltage value is related to the capacitance of the second absorption capacitor C4, the resistance of the second absorption resistor R2, and the duty cycle of the conduction time of the first switch Q1 and the second switch Q2.As can be seen, when the bus sampling voltage is less than the threshold voltage, the voltage difference of the primary coil will not be clamped to the input voltage. Therefore, the flyback converter circuit can work normally and will not have the problem that "the energy of the secondary coil is transferred back to the primary coil through the forward converter, so that the secondary coil can only get an output voltage that is slightly lower than the turns ratio of the bus voltage".

[0047] In some embodiments, the output voltage Vo of the flyback converter circuit (output by the secondary winding of transformer T through rectifier diode D) is typically adjustable. For example, in some scenarios, a 20V output is required, while in others, a 48V output is needed. The control unit can adjust the duty cycle of the first switch Q1 and the second switch Q2 to adjust the output voltage Vo of the flyback converter circuit to the new voltage value. When the output voltage Vo is adjusted to the new voltage value, the control unit updates the threshold voltage and outputs the updated threshold voltage to the voltage comparator circuit. Specifically, when the output voltage Vo is adjusted to a larger voltage value, the control unit updates the threshold voltage to a larger threshold voltage; when the output voltage Vo is adjusted to a smaller voltage value, the control unit updates the threshold voltage to a smaller threshold voltage. Finally, the control unit outputs the updated threshold voltage to the voltage comparator circuit. The voltage comparator circuit controls the third switch Q3 and the fourth switch Q4 to turn on or off based on the updated threshold voltage.

[0048] In some embodiments, the threshold voltage Vth is calculated and determined by the output voltage Vo and the voltage drop VD of the rectifier diode D: Vth = k*n*(Vo+VD); where n is the turns ratio of the primary and secondary windings of the transformer T, and k is the sampling coefficient, ranging from (0, 1), i.e., k = V'in / Vin (Vin is the bus voltage, V'in is the bus sampling voltage). In the above relationship, the instantaneous oscillation or fluctuation of the voltage difference across the primary winding of the transformer T when the first switch Q1 and the second switch Q2 are turned off is ignored. It is generally considered that the threshold voltage Vth = k*n*(Vo+VD) is quite appropriate. The flyback converter circuit works normally in the input voltage range Vin.min-Vth, and the voltage at the second end of the primary winding of the transformer T will not be clamped at -VD2; while in the input voltage range Vth-Vin.max, it has the advantages of a traditional two-transistor flyback converter circuit; where Vin.min and Vin.max are the minimum and maximum values ​​of the input voltage, respectively.

[0049] In some embodiments, if the instantaneous oscillation or fluctuation of the voltage difference across the primary winding of transformer T when the first switch Q1 and the second switch Q2 are turned off is taken into account, some margin can be added to the above threshold voltage Vth. That is, the magnitude of the threshold voltage Vth is calculated and determined by the output voltage Vo and the voltage drop VD of the rectifier diode D: Vth=k*(n*(Vo+VD)+V1); where V1 is a constant between 5V-10V.

[0050] As mentioned above, Figure 4 In the illustrated embodiment, the third switch Q3 can be positioned between the cathode of the first diode D1 and the busbar. The anode of the first diode D1 is connected to the first terminal T1 of the primary coil. The third switch Q3 is connected in parallel with the first absorption circuit, in which the first absorption capacitor C3 and the first absorption resistor R1 are connected in parallel. The fourth switch is positioned between the anode of the second diode D2 and ground. The operation of this flyback converter circuit during its duty cycle is similar to... Figure 3 The working principle of the flyback converter circuit is the same within the working cycle, but the specific process is different. For example, when the bus sampling voltage is less than the threshold voltage, in the working process step (3), when the first absorption capacitor C3 is charged to a certain voltage, the voltage difference between its high potential terminal P32 (correspondingly, P31 is its low potential terminal) and the first terminal T1 of the primary coil is less than the forward voltage drop of the first diode D1, and the charging of the first absorption capacitor C3 is cut off.

[0051] In some embodiments, such as Figure 5As shown, the flyback converter circuit also includes a third diode D3 and a fourth diode D4. A first absorption circuit is connected in series with the third diode D3 and then in parallel with the third switch Q3. At the instant the third switch Q3 is turned on, the third diode D3 prevents the charge of the first absorption capacitor C3 from discharging through the third switch Q3. After the third switch Q3 is turned off, the third diode D3 forms part of the first absorption clamping circuit. For example, the cathode of the third diode D3 is connected to the anode of the first diode D1, and the anode is connected to the low-potential terminal P31 of the absorption circuit. Alternatively, the cathode of the third diode D3 is connected to the high-potential terminal P32, and the anode is connected to the first terminal T1 of the primary coil (not shown in the figure). A second absorption circuit is connected in series with the fourth diode D4 and then in parallel with the fourth switch Q4. At the instant the fourth switch Q4 is turned on, the fourth diode D4 prevents the charge of the second absorption capacitor C4 from discharging through the fourth switch Q4. After the fourth switch Q4 is turned off, the fourth diode D4 forms part of the second absorption clamping circuit. For example, the cathode of the fourth diode D4 is connected to the anode of the second diode D2, and the anode is connected to the high-potential terminal P33 of the absorption circuit. As another example, the cathode of the fourth diode D4 is connected to the high-potential terminal P34 of the absorption circuit, and the anode is connected to ground (not shown in the figure). As mentioned earlier, when the bus sampling voltage is less than the threshold voltage, the first absorption capacitor C3 has a voltage value. When the bus sampling voltage changes to be greater than the threshold voltage, the third switch Q3 is controlled to conduct. Due to the presence of the third diode D3, the voltage on the first absorption capacitor C3 discharges through the first absorption resistor R1. Otherwise, if the third diode D3 is not present, at the instant the third switch Q3 is controlled to conduct, the first absorption capacitor C3 is short-circuited due to the conduction of the third switch Q3. The voltage of the first absorption capacitor C3 is instantaneously applied to the third switch Q3, generating a momentary high voltage, which can damage the third switch Q3. Similarly, when the bus sampling voltage is less than the threshold voltage, the second absorption capacitor C4 has a voltage value. When the bus sampling voltage changes to be greater than the threshold voltage, the third switch Q4 is controlled to conduct. Due to the presence of the fourth diode D4, the voltage on the second absorption capacitor C4 discharges through the second absorption resistor R2. Otherwise, if the fourth diode D4 is not present, at the moment the fourth switch Q4 is controlled to conduct, the second absorption capacitor C4 is short-circuited due to the conduction of the fourth switch Q4. The voltage of the second absorption capacitor C4 is instantaneously applied to the fourth switch Q4, generating a momentary high voltage, which will damage the fourth switch Q4. Likewise, Figure 4 The flyback converter circuit in the circuit may also include a third diode D3 and a fourth diode D4, which will not be elaborated here.

[0052] Figure 6 This is another embodiment of the flyback converter circuit of the present invention, which is related to... Figure 3They are basically similar, with the main differences being the relative positions of the first diode D1 and the third switch Q3, and the relative positions of the second diode D2 and the fourth switch Q4.

[0053] like Figure 6 As shown, specifically, the third switch Q3 is connected in series between the bus and the cathode of the first diode D1, the anode of the first diode D1 is connected to the first end T1 of the primary coil, and the fourth switch Q4 is connected in series between the cathode of the second diode D2 and the second end T2 of the primary coil.

[0054] The voltage comparator circuit compares the bus sampling voltage (i.e., the sampling voltage of the input voltage) V'in with the threshold voltage. When the bus sampling voltage is greater than the threshold voltage, the voltage comparator circuit controls the third switch Q3 to turn on and the fourth switch Q4 to turn on. This causes the first diode D1 and the third switch Q3 to form the first clamping circuit of the primary coil, and the fourth switch Q4 and the second diode D2 to form the second clamping circuit of the primary coil. The current in the first clamping circuit (also called the follow current, which is the current generated when the first switch Q1 and the second switch Q2 are turned off during the switching cycle of the first switch Q1 and the second switch Q2) is directed from the first terminal T1 of the primary coil, the anode of the first diode D1, the cathode of the first diode D1 to the third switch Q3, and causes the third switch Q3 to short-circuit the first absorption circuit. The current in the second clamping circuit is directed from the anode of the second diode D2, the cathode of the second diode D2, and from the fourth switch Q4 to the second terminal T2 of the primary coil, and causes the fourth switch Q4 to short-circuit the second absorption circuit. When the bus sampling voltage is less than the threshold voltage, the voltage comparison circuit controls the third switch Q3 to open and the fourth switch Q4 to open, so that the first diode D1 and the first absorption circuit form the first clamping absorption circuit of the primary coil, and the second diode D2 and the second absorption circuit form the second clamping absorption circuit of the primary coil.

[0055] When the bus sampling voltage is greater than the threshold voltage, the voltage comparison circuit obtains the comparison result by comparing the bus sampling voltage with the threshold voltage, and then controls the third switch Q3 to turn on. The third switch Q3 short-circuits the first absorption circuit, and controls the fourth switch Q4 to turn on. The fourth switch Q4 short-circuits the second absorption circuit. The working process of the flyback converter circuit during the working cycle is described in detail below: (1) The control unit controls the first switch Q1 and the second switch Q2 to turn on through the drive unit (not shown in the figure). The current flows out from the bus, passes through the first switch Q1, the primary coil and the second switch Q2 and flows into the ground. During this process, the current excites the transformer T, and the electrical energy is converted into magnetic energy. At this time, the rectifier diode D is cut off (i.e., turned off), and there is no current in the secondary coil. At this time, the voltage at the cathode of the second diode D2 is greater than the voltage at its anode, so the second diode D2 is cut off (i.e., turned off); the voltage at the cathode of the first diode D1 is greater than the voltage at its anode, so the first diode D1 is cut off (i.e., turned off); (2) After a certain period of time in step (1), the control unit controls the first switch Q1 and the second switch Q2 to open through the drive unit (not shown in the figure), the magnetic energy in the transformer T begins to be converted into electrical energy, the rectifier diode D is turned on, and there is current in the secondary coil; in addition, since the first switch Q1 and the second switch Q2 are opened instantaneously, the leakage inductance of the primary coil generates a large induced electromotive force; the output voltage Vo of the flyback converter circuit generates a reflected voltage in the primary coil due to the turns ratio of the transformer T (the turns ratio between the primary coil and the secondary coil), so the voltage difference across the primary coil is the sum of the induced electromotive force and the reflected voltage. Due to the clamping effect of the first diode D1, the voltage at the first terminal T1 of the primary coil is clamped at the sum of the input voltage and the voltage drop of the first diode D1 (i.e., Vin + VD1); due to the clamping effect of the second diode D2, the voltage at the second terminal T2 of the primary coil is clamped at the difference between 0 and the voltage drop of the second diode D2 (i.e., -VD2); thus, the freewheeling current in the primary coil flows out from the first terminal T1, flows through the first diode D1 into the bus, charges the bus capacitor C1, and the charging current returns to the second terminal T2 of the primary coil through the bus capacitor C1 and the second diode D2, forming a freewheeling current loop.

[0056] When the bus sampling voltage is less than the threshold voltage, the voltage comparison circuit obtains the comparison result by comparing the bus sampling voltage with the threshold voltage, and then controls the third switch Q3 and the fourth switch Q4 to open respectively, so that the first diode D1 and the first absorption circuit form the first clamping absorption circuit (RCD circuit) of the primary coil, and the second diode D2 and the second absorption circuit form the second clamping absorption circuit (RCD circuit) of the primary coil.

[0057] The working process of the flyback converter circuit during the working cycle is described in detail below: (1) The control unit controls the first switch Q1 and the second switch Q2 to be turned on through the drive unit (not shown in the figure). The current flows out from the bus, passes through the first switch Q1, the primary coil and the second switch Q2 and flows into the ground. During this process, the current excites the transformer T, and the electrical energy is converted into magnetic energy. At this time, the rectifier diode D is cut off (i.e., turned off) and there is no current in the secondary coil. At this time, the voltage at the cathode of the second diode D2 is greater than the voltage at its anode, so the second diode D2 is cut off (i.e., turned off); the voltage at the cathode of the first diode D1 is greater than the voltage at its anode, so the first diode D1 is cut off (i.e., turned off); (2) After a certain period of time in step (1), the control unit controls the first switch Q1 and the second switch Q2 to open through the drive unit (not shown in the figure), the magnetic energy in the transformer T begins to be converted into electrical energy, the rectifier diode D is turned on, and there is current in the secondary coil; in addition, since the first switch Q1 and the second switch Q2 are opened instantaneously, the leakage inductance of the primary coil generates a large induced electromotive force; the output voltage Vo of the flyback converter circuit generates a reflected voltage in the primary coil due to the turns ratio of the transformer T (the turns ratio between the primary coil and the secondary coil), that is, the voltage difference across the primary coil is the sum of the induced electromotive force and the reflected voltage. When the first diode D1 is turned on, the first absorption capacitor C3 begins to charge. The charging current flows out from the first terminal T1 of the primary coil, passes through the first diode D1, and charges the first absorption capacitor C3 before flowing back to the second terminal T2 of the primary coil. In addition, when the second diode D2 is turned on, the second absorption capacitor C4 begins to charge. The charging current passes through the second diode D2 and charges the second absorption capacitor C4 before flowing back to the second terminal T2 of the primary coil.Due to the charging effect of the first absorption capacitor C3 and the second absorption capacitor C4, the voltage spikes caused by the induced electromotive force in the voltage of the first terminal T1 and the second terminal T2 of the primary coil are also absorbed and become smooth (3). When the first absorption capacitor C3 is charged to a certain voltage, the voltage difference between its high potential terminal P32 and the first terminal of the primary coil is less than the forward voltage drop of the first diode D1, the charging of the first absorption capacitor C3 is cut off (i.e., turned off). At this time, when the second absorption capacitor C4 is charged to a certain voltage, the voltage difference between its high potential terminal P34 and ground is less than the forward voltage drop of the second diode D2, the charging of the second absorption capacitor C4 is cut off (i.e., turned off); (4) The first absorption capacitor C 3. Discharge can be achieved through the first absorption resistor R1. The discharge current flows out from the high-potential terminal P32 of the first absorption capacitor C3 (the end that shares the same point as the cathode of the first diode), passes through the first absorption resistor R1, and flows into the low-potential terminal P31 of the first absorption capacitor C3 (the end connected to the busbar). Similarly, the second absorption capacitor C4 can be discharged through the second absorption resistor R2. The discharge current flows out from the high-potential terminal P34 of the second absorption capacitor C4 (the end that shares the same point as the cathode of the second diode), passes through the second absorption resistor R2, and flows into the low-potential terminal P33 of the second absorption capacitor C4 (the end connected to the second terminal of the primary coil). After discharging to a certain voltage value, the excitation reverses. The circuit then enters the next cycle's steps (1)-(3). In step (1) of this next cycle, the cathode voltage of the first diode D1 is the voltage of the high-potential terminal P32, and its anode voltage is the voltage of the first terminal T1 of the primary coil. At this time, the first diode D1 is cut off. The cathode voltage of the second diode D2 is the voltage of the high-potential terminal P34, and its anode voltage is ground. At this time, the second diode D2 is cut off. After step (3) of this next cycle, the first absorption capacitor C3 and the second absorption capacitor C4 start charging again. Therefore, when the bus sampling voltage is less than the threshold voltage, the flyback converter circuit will charge the first absorption capacitor during operation. The voltage VC3 at the high-potential terminal P32 of capacitor C3 can be stably maintained above a certain voltage value (i.e., it can store at least a certain amount of electrical energy). This voltage value is related to the capacitance of the first absorption capacitor C3, the resistance of the first absorption resistor R1, and the duty cycle of the conduction time of the first switch Q1 and the second switch Q2. Similarly, the voltage at the low-potential terminal P33 of the second absorption capacitor C4 can be stably maintained below a certain voltage value (negative value) (i.e., it can store at least a certain amount of electrical energy). This voltage value is related to the capacitance of the second absorption capacitor C4, the resistance of the second absorption resistor R2, and the duty cycle of the conduction time of the first switch Q1 and the second switch Q2. Therefore, when the bus sampling voltage is less than the threshold voltage, the voltage difference of the primary winding will not be clamped to the input voltage. Thus, the flyback converter circuit can operate normally, and the problem of "the energy of the secondary winding being transferred back to the primary winding via a forward converter, resulting in the secondary winding only obtaining an output voltage with a turns ratio slightly lower than the bus voltage" will not occur.

[0058] As mentioned above, Figure 7 In the illustrated embodiment, the third switch Q3 can be positioned between the anode of the first diode D1 and the first terminal T1 of the primary winding, with the cathode of the first diode D1 connected to the bus. The fourth switch Q4 can be positioned between the second terminal T2 of the primary winding and the cathode of the second diode D2, with the anode of the second diode D2 grounded. The operation of this flyback converter circuit during its duty cycle is similar to... Figure 6 The working principle of flyback converter circuits is the same within the duty cycle, but the specific processes are different.

[0059] In some embodiments, such as Figure 8 As shown, the flyback converter circuit also includes a third diode D3, a fourth diode D4, a first absorption circuit connected in series with the third diode D3 and then in parallel with the third switch Q3, and the cathode of the third diode D3 and the third switch Q3 share a common terminal. In the first absorption circuit, the current direction is from the anode of the third diode D3 to the cathode of the third diode D3. The function of the fourth diode D4 has been described in detail in the aforementioned related embodiments and will not be repeated here. Similarly, Figure 7 The flyback converter circuit in the circuit may also include a third diode D3 and a fourth diode D4, which will not be elaborated here.

[0060] Those skilled in the art will understand that, without conflict, the above-mentioned preferred solutions can be freely combined and superimposed.

[0061] Those skilled in the art will understand that, without conflict, the above-mentioned preferred solutions can be freely combined and superimposed.

[0062] It should be understood that the above embodiments are merely exemplary and not restrictive. Various obvious or equivalent modifications or substitutions that can be made by those skilled in the art regarding the above details without departing from the basic principles of the present invention will be included within the scope of the claims of the present invention.

Claims

1. A flyback converter circuit, comprising a first switch, a second switch, a first diode, and a second diode, characterized in that, Also includes: The circuit includes a third switch, a fourth switch, a voltage comparison circuit, a first absorption circuit, and a second absorption circuit. The first absorption circuit includes a first absorption capacitor and a first absorption resistor, and the second absorption circuit includes a second absorption capacitor and a second absorption resistor. One end of the first switch is connected to the busbar, and the other end is connected to the second end of the primary winding of the transformer; one end of the second switch is connected to the first end of the primary winding, and the other end is grounded. The first diode and the third switch are connected in series between the busbar and the first end of the primary coil. The third switch is connected in parallel with the first absorption circuit. In the first absorption circuit, the first absorption capacitor and the first absorption resistor are connected in parallel. The second diode and the fourth switch are connected in series between the second end of the primary coil and ground; the fourth switch is connected in parallel with the second absorption circuit, in which the second absorption capacitor and the second absorption resistor are connected in parallel; The voltage comparison circuit compares the bus sample voltage with a threshold voltage. When the bus sample voltage is greater than the threshold voltage: the voltage comparison circuit controls the third switch to turn on, thereby forming a first clamping circuit for the primary coil with the first diode and the third switch. The current direction in the first clamping circuit is from the first end of the primary coil, the anode of the first diode to the cathode of the first diode, and the third switch short-circuits the first absorption circuit. The voltage comparison circuit also controls the fourth switch to turn on, thereby forming a second clamping circuit for the primary coil with the second diode and the fourth switch. The current direction in the second clamping circuit is from the anode of the second diode, the cathode of the second diode to the second end of the primary coil, and the fourth switch short-circuits the second absorption circuit. When the bus sampling voltage is less than the threshold voltage: the voltage comparison circuit controls the third switch to open, thereby causing the first diode and the first absorption circuit to form the first clamping absorption circuit of the primary coil. The voltage comparison circuit also controls the fourth switch to open, thereby causing the second diode and the second absorption circuit to form the second clamping absorption circuit of the primary coil.

2. The flyback converter circuit according to claim 1, characterized in that, It also includes a third diode and a fourth diode. The first absorption circuit is connected in series with the third diode and then in parallel with the third switch. When the third switch is turned on, the third diode is used to prevent the charge of the first absorption capacitor from discharging through the third switch. After the third switch is turned off, the third diode constitutes a component of the first clamping absorption circuit. The second absorption circuit is connected in series with the fourth diode and then in parallel with the fourth switch. When the fourth switch is turned on, the fourth diode is used to prevent the charge of the second absorption capacitor from discharging through the fourth switch. After the fourth switch is turned off, the fourth diode constitutes a component of the second clamping absorption circuit.

3. The flyback converter circuit according to claim 1, characterized in that, It also includes a control unit, wherein the secondary coil of the transformer outputs the output voltage through a rectifier diode; The control unit is used for: When the output voltage of the flyback converter circuit is adjusted to a new voltage value, the threshold voltage is updated according to the following relationship between the threshold voltage and the output voltage: Vth=k*n*(Vo+Vd); where Vth, Vo and Vd are the threshold voltage, the output voltage and the voltage drop of the rectifier diode, respectively, n is the turns ratio of the primary and secondary coils of the transformer, and k is the sampling coefficient, with a value range of (0, 1). The updated threshold voltage is output to the voltage comparison circuit.

4. The flyback converter circuit according to claim 1, characterized in that, It also includes a control unit, wherein the secondary coil of the transformer outputs the output voltage through a rectifier diode; The control unit is used for: When the output voltage of the flyback converter circuit is adjusted to a new voltage value, the threshold voltage is updated according to the following relationship between the threshold voltage and the output voltage: Vth = k*(n*(Vo+Vd)+V1); where Vth, Vo, and Vd are the threshold voltage, the output voltage, and the voltage drop of the rectifier diode, respectively; V1 is a constant between 5V and 10V; n is the turns ratio of the primary and secondary windings of the transformer; and k is a sampling coefficient with a value range of (0, 1). The updated threshold voltage is output to the voltage comparison circuit.

5. A control method for a flyback converter circuit, characterized in that, Using the flyback converter circuit as described in claim 1, the control method includes the following steps: The voltage comparison circuit compares the bus sample voltage with a threshold voltage. When the bus sample voltage is greater than the threshold voltage: the voltage comparison circuit controls the third switch to turn on, thereby causing the first diode and the third switch to form a first clamping circuit for the primary coil. The current direction in the first clamping circuit is from the first end of the primary coil, the anode of the first diode, to the cathode of the first diode, and the third switch short-circuits the first absorption circuit. The voltage comparison circuit also controls the fourth switch to turn on, thereby causing the second diode and the fourth switch to form a second clamping circuit for the primary coil. The current direction in the second clamping circuit is from the anode of the second diode, the cathode of the second diode, to the second end of the primary coil, and the fourth switch short-circuits the second absorption circuit. When the bus sampling voltage is less than the threshold voltage: the voltage comparison circuit controls the third switch to open, thereby causing the first diode and the first absorption circuit to form the first clamping absorption circuit of the primary coil. The voltage comparison circuit also controls the fourth switch to open, thereby causing the second diode and the second absorption circuit to form the second clamping absorption circuit of the primary coil.

6. The control method as described in claim 5, characterized in that, The flyback converter circuit also includes a control unit, and the secondary coil of the transformer outputs the output voltage through a rectifier diode; The control method further includes the following steps: When the output voltage of the flyback converter circuit is adjusted to a new voltage value, the control unit updates the threshold voltage according to the following relationship between the threshold voltage and the output voltage: Vth=k*n*(Vo+Vd); where Vth, Vo, and Vd are the threshold voltage, the output voltage, and the voltage drop of the rectifier diode, respectively; n is the turns ratio of the primary and secondary windings of the transformer; and k is a sampling coefficient with a value range of (0, 1). The control unit outputs the updated threshold voltage to the voltage comparison circuit.

7. The control method according to claim 5, characterized in that, The flyback converter circuit also includes a control unit, and the secondary coil of the transformer outputs the output voltage through a rectifier diode; The control method further includes the following steps: When the output voltage of the flyback converter circuit is adjusted to a new voltage value, the control unit updates the threshold voltage according to the following relationship between the threshold voltage and the output voltage: Vth=k*(n*(Vo+Vd)+V1); where Vth, Vo, and Vd are the threshold voltage, the output voltage, and the voltage drop of the rectifier diode, respectively; V1 is a constant between 5V and 10V; n is the turns ratio of the primary and secondary windings of the transformer; and k is a sampling coefficient with a value range of (0, 1). The control unit outputs the updated threshold voltage to the voltage comparison circuit.

8. A flyback converter, comprising a transformer, characterized in that, It also includes the flyback converter circuit as described in any one of claims 1-4.

9. A servo motor driver, comprising a transformer, characterized in that, It also includes the flyback converter circuit as described in any one of claims 1-4.

10. A servo motor, characterized in that, Includes the servo motor driver as described in claim 9.

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