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. The first switch has one end connected with a bus and the other end connected with the second end of a primary winding of a transformer. The second switch has one end connected with the first end of the primary winding and the other end grounded. The anode of the first diode is connected with the first end of the primary winding, and the cathode is connected with the bus. The second diode is connected in series with the third switch between the second end of the primary winding and the ground. The third switch is connected in parallel with an absorption circuit, and the absorption capacitor and the absorption resistor in the absorption circuit are connected in parallel. When the bus sampling voltage is greater than a threshold voltage, the voltage comparison circuit controls the third switch to be turned on, so that the second diode and the third switch form a clamping circuit of the primary winding, and the third switch short-circuits the absorption circuit. When the bus sampling voltage is less than the threshold voltage, the voltage comparison circuit controls the third switch to be turned off, so that the second diode and the absorption circuit form a clamping absorption circuit of the primary winding.

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] Flyback converter topologies are widely used in low-power switching power supplies (below 200W) and auxiliary power supplies for various electronic devices due to their low cost, high reliability, and excellent performance. Flyback converters can be further classified into single-transistor flyback converters and two-transistor flyback converters based on the number of switches connected in series with the primary coil and the different connection structures.

[0003] In a single-transistor flyback converter, the switching transistor connected in series with the primary winding needs 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 the transistor is turned off (induced electromotive force generated by the leakage inductance of the primary winding). Under high input voltage conditions, the switching transistor needs to withstand higher voltage ratings, which significantly limits the maximum input voltage of this topology. However, with proper design, theoretically, a single-transistor flyback converter can still output normally at extremely low input voltages.

[0004] In a two-transistor flyback converter, 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 input bus through the clamping diodes. This allows the switching transistors to only withstand the bus voltage, making this topology easier to apply under high input voltage conditions. However, at low input voltages, 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 via a forward converter. This results in the secondary winding only outputting a 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, where Vo, Vin, and VD are the output voltage, the bus input voltage, and the voltage drop across the rectifier diodes, respectively.

[0005] Traditional two-transistor flyback converters have problems with low input voltage. Designers can only avoid this range and determine the minimum input voltage at the beginning of the design. Even so, it is impossible to take into account both the minimum and maximum input voltages with a wide range of inputs.

[0006] It can be seen that single-transistor flyback converters have no advantage at high input voltages, while dual-transistor flyback converters have problems at low input voltages.

[0007] As an example, supercapacitors are now widely used as backup power in servo drive applications, especially in wind turbine pitch servo drives. When the grid is powered, three-phase 400Vac AC power is input to the AC rectifier circuit, and the bus voltage after rectification can reach 800Vdc under extreme conditions. When the grid is de-energized, and the supercapacitor is needed as a backup power source, its voltage needs to be released as low as possible to maximize the utilization of its energy, ideally to zero. Therefore, the operating voltage range of the bus voltage is between tens of volts and 800Vdc, a requirement that current single-tube and dual-tube flyback converters cannot meet. Summary of the Invention

[0008] 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.

[0009] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0010] A flyback converter circuit includes a first switch, a second switch, a first diode, and a second diode, characterized in that it further includes: a third switch, a voltage comparator circuit, and an absorption circuit, wherein the absorption circuit includes an absorption capacitor and an 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 a transformer; one end of the second switch is connected to the first end of the primary winding, and the other end is grounded; the anode of the first diode is connected to the first end of the primary winding, and the cathode is connected to the bus; the second diode and the third switch are connected in series between the second end of the primary winding and ground; the third switch is connected in parallel with the absorption circuit, wherein the absorption capacitor and absorption resistor in the absorption circuit... The voltage comparison circuit compares the bus sampling voltage with the threshold voltage. When the bus sampling voltage is greater than the threshold voltage, the voltage comparison circuit controls the third switch to turn on, thereby forming a clamping circuit for the primary coil with the second diode and the third switch. The current direction in the clamping circuit is from the anode and cathode of the second diode to the second end of the primary coil, and the third switch short-circuits the absorption circuit. When the bus sampling voltage is less than the threshold voltage, the voltage comparison circuit controls the third switch to turn off, thereby forming a clamping absorption circuit for the primary coil with the second diode and the absorption circuit.

[0011] Preferably, the flyback converter circuit further includes a third diode. The 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 absorption capacitor from discharging through the third switch. After the third switch is turned off, the third diode constitutes a component of the absorption clamping circuit.

[0012] Preferably, the flyback converter circuit further includes a control unit. When the output voltage of the flyback converter circuit is adjusted to a new voltage value, the control unit updates the threshold voltage and outputs the updated threshold voltage to the voltage comparison circuit.

[0013] Preferably, the secondary winding of the transformer outputs the output voltage through a rectifier diode. 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 winding and the secondary winding of the transformer, and k is a sampling coefficient with a value range of (0, 1).

[0014] Preferably, the secondary winding of the transformer outputs the output voltage through a rectifier diode. 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 winding and the secondary winding of the transformer; and k is a sampling coefficient with a value range of (0, 1).

[0015] 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 sampling voltage with a threshold voltage. When the bus sampling voltage is greater than the threshold voltage, the voltage comparator circuit controls the third switch to turn on, thereby causing the second diode and the third switch to form a clamping circuit for the primary coil. The current direction in the clamping circuit is from the anode and cathode of the second diode to the second end of the primary coil, and the third switch short-circuits the absorption circuit. When the bus sampling voltage is less than the threshold voltage, the voltage comparator circuit controls the third switch to turn off, thereby causing the second diode and the absorption circuit to form a clamping absorption circuit for the primary coil.

[0016] Preferably, the flyback converter circuit further includes a control unit, and the control method further includes the step of: when the output voltage of the flyback converter circuit is adjusted to a new voltage value, the control unit updates the threshold voltage and outputs the updated threshold voltage to the voltage comparison circuit.

[0017] Preferably, the secondary coil of the transformer outputs the output voltage through a rectifier diode, and 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, and n is the turns ratio of the primary coil and the secondary coil of the transformer.

[0018] Preferably, the secondary winding of the transformer outputs the output voltage through a rectifier diode. 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 winding and the secondary winding of the transformer; and k is a sampling coefficient with a value range of (0, 1).

[0019] This invention also provides a flyback converter circuit, including a first switch, a second switch, a first diode, a second diode, and further comprising: a third switch, a voltage comparator circuit, and an absorption circuit, wherein the absorption circuit includes an absorption capacitor and an 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 cathode of the second diode is connected to the second end of the primary winding, and the anode is grounded; the first diode and the third switch are connected in series between the first end of the primary winding and the bus; the third switch is connected in parallel with the absorption circuit, wherein the absorption capacitor and absorption resistor in the absorption circuit... The resistors are connected in parallel; the voltage comparison circuit compares the bus sampling voltage with the threshold voltage. When the bus sampling voltage is greater than the threshold voltage, the voltage comparison circuit controls the third switch to turn on, thereby forming a clamping circuit for the primary coil with the first diode and the third switch. The current direction in the clamping circuit is from the anode and cathode of the first diode to the bus, and the third switch short-circuits the absorption circuit. When the bus sampling voltage is less than the threshold voltage, the voltage comparison circuit controls the third switch to turn off, thereby forming a clamping absorption circuit for the primary coil with the first diode and the absorption circuit.

[0020] Preferably, the flyback converter circuit further includes a third diode. The 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 absorption capacitor from discharging through the third switch. After the third switch is turned off, the third diode constitutes a component of the absorption clamping circuit.

[0021] Preferably, the flyback converter circuit further includes a control unit. When the output voltage of the flyback converter circuit is adjusted to a new voltage value, the control unit updates the threshold voltage and outputs the updated threshold voltage to the voltage comparison circuit.

[0022] Preferably, the secondary winding of the transformer outputs the output voltage through a rectifier diode. 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 winding and the secondary winding of the transformer, and k is a sampling coefficient with a value range of (0, 1).

[0023] Preferably, the secondary winding of the transformer outputs the output voltage through a rectifier diode. 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 winding and the secondary winding of the transformer; and k is a sampling coefficient with a value range of (0, 1).

[0024] 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 turn on, thereby causing the first diode and the third switch to form a clamping circuit for the primary coil, and the current direction in the clamping circuit is from the anode and cathode of the first diode to the bus, and causing the third switch to short-circuit the absorption circuit; when the bus sampled voltage is less than the threshold voltage, the voltage comparator circuit controls the third switch to turn off, thereby causing the first diode and the absorption circuit to form a clamping absorption circuit for the primary coil.

[0025] Preferably, the flyback converter circuit further includes a control unit, and the control method further includes the step of: when the output voltage of the flyback converter circuit is adjusted to a new voltage value, the control unit updates the threshold voltage and outputs the updated threshold voltage to the voltage comparison circuit.

[0026] Preferably, the secondary winding of the transformer outputs the output voltage through a rectifier diode. 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 winding and the secondary winding of the transformer, and k is a sampling coefficient with a value range of (0, 1).

[0027] Preferably, the secondary winding of the transformer outputs the output voltage through a rectifier diode. 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 winding and the secondary winding of the transformer; and k is a sampling coefficient with a value range of (0, 1).

[0028] The present invention also provides a flyback converter, including a transformer, and further including any of the flyback converter circuits described above.

[0029] The present invention also provides a servo motor driver, including a transformer and any of the flyback converter circuits described above.

[0030] The present invention also provides a servo motor, including the aforementioned servo motor driver.

[0031] [Beneficial Effects]

[0032] When the bus sampling voltage is greater than the threshold voltage, the voltage comparator circuit controls the third switch to turn on, thereby forming a clamping circuit for the primary coil with the second diode and the third switch, similar to a two-transistor flyback converter. The withstand voltage values ​​of the first and second switches can be relatively low. When the bus sampling voltage is less than the threshold voltage, the voltage comparator circuit controls the third switch to turn off, thereby forming a clamping absorption circuit for the primary coil with the second diode and the absorption circuit. The first or second end 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 the forward converter, so that the secondary coil can only get 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 relatively low.

[0033] 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 the technical features and technical solutions through the introduction of these technical features and technical solutions. Attached Figure Description

[0034] 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:

[0035] Figure 1 This is a schematic diagram of the circuit topology of a single-transistor flyback converter circuit in the prior art;

[0036] Figure 2 This is a schematic diagram of the circuit topology of a dual-transistor flyback converter circuit in the prior art;

[0037] Figure 3 This is a flyback converter circuit according to a preferred embodiment of the present invention;

[0038] Figure 4 This is a flyback converter circuit according to another preferred embodiment of the present invention;

[0039] Figure 5 This is a flyback converter circuit according to another preferred embodiment of the present invention;

[0040] Figure 6 This is a flyback converter circuit according to another preferred embodiment of the present invention;

[0041] Figure 7 This is a flyback converter circuit according to another preferred embodiment of the present invention;

[0042] Figure 8 This is a flyback converter circuit according to another preferred embodiment of the present invention. Detailed Implementation

[0043] 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.

[0044] 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.

[0045] 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."

[0046] 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.

[0047] 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).

[0048] 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 voltage comparator circuit, an absorption circuit, a transformer T, a rectifier diode D, and an output filter capacitor C2. The absorption circuit includes an absorption capacitor C3 and an absorption resistor R1. The first switch Q1, the second switch Q2, and the third switch Q3 can be MOSFETs, such as N-channel MOSFETs or P-channel MOSFETs, and IGBTs (Insulated Gate Bipolar Transistors).

[0049] 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.

[0050] The first switch Q1 is connected at one end to the busbar and at the other end to the second terminal T2 of the primary winding of transformer T; the second switch Q2 is connected at one end to the first terminal T1 of the primary winding and at the other end to ground. The anode of the first diode D1 is connected to the first terminal T1 of the primary winding, and the cathode is connected to the busbar. The second diode D2 and the third switch Q3 are connected in series between the second terminal T2 of the primary winding and ground; in one embodiment, as shown... Figure 3 As shown, the third switch Q3 can be positioned between the anode of the second diode D2 and ground, and the cathode of the second diode D2 is connected to the second terminal T2 of the primary coil; in another embodiment, as... Figure 4 As shown, the third switch Q3 can be placed between the cathode of the second diode D2 and the second terminal T2 of the primary coil, with the anode of the second diode D2 grounded. The third switch Q3 is connected in parallel with the absorption circuit, in which the absorption capacitor C3 and the absorption resistor R1 are connected in parallel.

[0051] 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, thereby forming a clamping circuit for the primary coil with the second diode D2 and the third switch Q3. The current in the 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 their switching cycles) is directed from the anode and cathode of the second diode D2 to the second terminal T2 of the primary coil, and causes the third switch Q3 to short-circuit the absorption circuit. When the bus sampling voltage is less than the threshold voltage, the voltage comparator circuit controls the third switch Q3 to turn off, thereby forming a clamping absorption circuit for the primary coil with the second diode D2 and the absorption circuit. Figure 3As shown, in one embodiment, the voltage comparison circuit employs a comparator, with one end receiving the bus sampling voltage (i.e., the sampling voltage of the input voltage) and the other end receiving the threshold voltage. The output terminal outputs a comparison result signal; for example, the comparison result signal is high when the sampling voltage of the input voltage is greater than the threshold voltage, and low when it is less than the threshold voltage. In some embodiments, the flyback converter circuit further includes a drive circuit that converts the comparison result signal into a drive signal for driving the third switch Q3, inputting it to the control terminal of the third switch Q3 to control the third switch Q3 to turn on or off. For example, the third switch Q3 is a MOSFET, and the drive signal is input to the gate of the MOSFET. A resistor R2 is connected between the gate and source, which 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.

[0052] 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 the filter capacitor 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.

[0053] When the bus sampling voltage is greater than the threshold voltage, the voltage comparison circuit controls the third switch Q3 to turn on after obtaining the comparison result by comparing the bus sampling voltage with the threshold voltage. The third switch Q3 short-circuits the 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.

[0054] 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 to open. The second diode D2 and the absorption circuit form a clamping absorption circuit (RCD circuit) for the primary coil, similar to a traditional single-tube flyback converter. 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. Due to the clamping effect of the first diode D1, the voltage at the first terminal T1 of the primary coil is clamped to the sum of the input voltage and the voltage drop across the first diode D1 (i.e., Vin + VD1). The freewheeling current in the primary coil flows out from the first terminal T1, through the first diode D1, and into the bus, charging the bus capacitor C1. Because the voltage at the first terminal T1 of the primary coil is clamped, the voltage at the second terminal T2 of the primary coil (the voltage at the second terminal T2 of the primary coil is negative) is approximately equal to the bus voltage minus the sum of the induced electromotive force and the reflected voltage. The second diode D2 conducts, and the absorption capacitor C3 begins to charge. The charging current flows back to the second terminal T2 of the primary coil after passing through the absorption capacitor C3 and the second diode D2.Due to the charging effect of the absorption capacitor C3, the voltage spike caused by the induced electromotive force in the voltage of the second terminal T2 of the primary coil is also absorbed and becomes smooth; (3) When the absorption capacitor C3 is charged to a certain voltage, the voltage difference between it and the second terminal T2 of the primary coil is less than the forward voltage drop of the second diode D2, the charging of the absorption capacitor C3 is cut off (i.e., turned off); (4) The absorption capacitor C3 can be discharged through the absorption resistor R1. The discharge current flows out from the high potential terminal P32 (the end connected to ground) of the absorption capacitor C3, and flows into the low potential terminal P31 (the end that is common to the anode of the second diode D2) of the absorption capacitor C3 after passing through the absorption resistor R1. After discharging to a certain voltage value, the flyback converter circuit starts to enter the next cycle of steps (1)-(3). In step (1) of the next cycle, the cathode voltage of the second diode D2 is the bus voltage, and its anode voltage is the negative voltage of the low potential terminal P31. At this time, the second diode D2 is turned off; after step (3) of the next cycle, the absorption capacitor C3 starts to charge again. Therefore, when the bus sampling voltage is less than the threshold voltage, during operation of the flyback converter circuit, the voltage VC3 at the low-potential terminal P31 of the absorption capacitor C3 can be stably 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 absorption capacitor C3, the resistance of the absorption resistor R1, and the duty cycle of the conduction time of the first switch Q1 and the second switch Q2. It can be seen that when the bus voltage is less than the threshold voltage, the second terminal T2 of the primary coil will not be clamped to the input voltage. Therefore, the flyback converter circuit can operate normally, and the problem of "the energy of the secondary coil being transferred back to the primary coil through a forward converter, resulting in the secondary coil only obtaining an output voltage with a turns ratio slightly lower than the bus voltage" will not occur.

[0055] 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 output voltage Vo of the flyback converter circuit to the new voltage value by adjusting the duty cycle of the first switch Q1 and the second switch Q2. 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 to turn on or off based on the updated threshold voltage.

[0056] 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.

[0057] 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.

[0058] As mentioned above, Figure 4 In the illustrated embodiment, the third switch Q3 can be positioned between the cathode of the second diode D2 and the second terminal T2 of the primary coil, with the anode of the second diode D2 grounded. 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 in 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 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 ground (voltage is 0) is less than the forward voltage drop of the second diode D2, and the charging of the absorption capacitor C3 is cut off.

[0059] In some embodiments, such as Figure 5As shown, the flyback converter circuit also includes a third diode D3. The absorption circuit is connected in series with the third diode D3 and then in parallel with the third switch Q3. When the third switch Q3 is turned on, the third diode D3 prevents the charge in the absorption capacitor from discharging through the third switch Q3. When the third switch Q3 is turned off, the third diode D3 forms part of the 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 can be connected to the high-potential terminal P32, and the anode can be grounded (not shown in the figure). As mentioned earlier, when the bus sampling voltage is less than the threshold voltage, the 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 absorption capacitor C3 discharges through the absorption resistor R1. Otherwise, if the third diode D3 is not present, at the moment the third switch Q3 is controlled to conduct, the absorption capacitor C3 is short-circuited due to the conduction of the third switch Q3. The voltage of the absorption capacitor C3 is instantaneously applied to the third switch Q3, generating a momentary high voltage, which will damage the third switch Q3. Similarly, Figure 4 The flyback converter circuit in the circuit may also include a third diode D3, which will not be elaborated here.

[0060] Figure 6 This is another embodiment of the flyback converter circuit of the present invention, which is related to... Figure 3 The flyback converter circuit is largely similar.

[0061] 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 and an AC rectifier circuit, which operate under corresponding conditions. When the grid is powered, the AC rectifier circuit operates, converting the AC voltage into DC voltage to supply the bus. When the grid is de-powered, the supercapacitor operates, and its output DC voltage is supplied to the bus.

[0062] The first switch Q1 is connected at one end to the busbar and at the other end to the second terminal T2 of the primary winding of transformer T; the second switch Q2 is connected at one end to the first terminal T1 of the primary winding and at the other end to ground. The cathode of the second diode D2 is connected to the second terminal T2 of the primary winding, and the anode is grounded. The first diode D1 and the third switch Q3 are connected in series between the busbar and the first terminal T1 of the primary winding; in one embodiment, as... Figure 6 As shown, the third switch Q3 can be positioned between the anode of the first diode D1 and the first terminal T1 of the primary coil, with the cathode of the first diode D1 connected to the busbar; in another embodiment, as... Figure 7As shown, the third switch Q3 can be placed between the busbar and the cathode of the first diode D1, and 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 absorption circuit, in which the absorption capacitor C3 and the absorption resistor R1 are connected in parallel.

[0063] 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, thereby forming a clamping circuit for the primary coil with the first diode D1 and the third switch Q3. The current in the 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 their switching cycles) is directed from the anode and cathode of the first diode D1 to the bus, and the third switch Q3 short-circuits the absorption circuit. When the bus sampling voltage is less than the threshold voltage, the voltage comparator circuit controls the third switch Q3 to turn off, thereby forming a clamping absorption circuit for the primary coil with the first diode D1 and the absorption circuit. Figure 6 As 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 sampling voltage of 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 a drive signal for driving the third switch Q3 and inputs it to the control terminal of the third switch Q3 to control the third switch Q3 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 R2 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 channel for the accumulated charge on the gate.

[0064] 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 the filter capacitor 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.

[0065] When the bus sampling voltage is greater than the threshold voltage, the voltage comparison circuit controls the third switch Q3 to turn on after obtaining the comparison result by comparing the bus sampling voltage with the threshold voltage. The third switch Q3 short-circuits the 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.

[0066] 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 to open. The first diode D1 and the absorption circuit form a clamping absorption circuit for the primary coil. 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. 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). The charging current on the bus capacitor C1 flows out from the bus capacitor C1, passes through the second diode D2, and flows into the second terminal T2 of the primary coil. Because the voltage at the second terminal T2 of the primary coil is clamped, the voltage at the first terminal T1 of the primary coil (the voltage at the first terminal T1 of the primary coil is positive) is approximately equal to the sum of the induced electromotive force and the reflected voltage. The first diode D1 conducts, and the absorption capacitor C3 begins to charge. The charging current flows out from the first terminal T1 of the primary coil, passes through the absorption capacitor C3 and the first diode D1, and flows back to the bus to charge the bus capacitor C1.Due to the charging effect of the absorption capacitor C3, the voltage spike caused by the induced electromotive force in the voltage of the first terminal T1 of the primary coil is also absorbed and becomes smooth; (3) When the high potential terminal of the absorption capacitor C3 is charged to a certain voltage, and the voltage difference between the low potential terminal of the absorption capacitor C3 and the bus is less than the forward voltage drop of the second diode D2, the charging of the absorption capacitor C3 is cut off (i.e., turned off); (4) The absorption capacitor C3 can be discharged through the absorption resistor R1, and the discharge current flows from the high potential terminal P32 of the absorption capacitor C3 (connected to the first terminal T1 of the primary coil) to the high potential terminal P32 of the absorption capacitor C3. The current flows out from the end of the capacitor, passes through the absorption resistor R1, and flows into the low potential end P31 of the absorption capacitor C3 (the end that shares the same point as the anode of the first diode D1). After discharging to a certain voltage value, the flyback converter circuit begins to enter the next cycle of steps (1)-(3). In step (1) of the next cycle, the cathode voltage of the first diode D1 is the bus voltage, and its anode voltage is the voltage of the low potential end P31. At this time, the first diode D1 is cut off. After step (3) of the next cycle, the absorption capacitor C3 starts to charge again. Therefore, when the bus sampling voltage is less than the threshold voltage, the voltage VC3 of the high potential end P32 of the absorption capacitor C3 can be stably maintained below a certain voltage value (i.e., at least a certain amount of electrical energy can be stored) during the operation of the flyback converter circuit. This voltage value is related to the capacitance value of the absorption capacitor C3, the resistance value of the absorption resistor R1, 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 at the first terminal T1 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 fed 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".

[0067] Similarly, in some embodiments, when the output voltage Vo is adjusted to a 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 the larger threshold voltage; when the output voltage Vo is adjusted to a smaller voltage value, the control unit updates the threshold voltage to the 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 to turn on or off based on the updated threshold voltage.

[0068] 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. 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. This flyback converter circuit operates normally within the input voltage range Vin.min-Vth, and the voltage at the second terminal of the primary winding of the transformer T will not be clamped at -VD2. Furthermore, within the input voltage range Vth-Vin.max, it possesses 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.

[0069] 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.

[0070] As mentioned above, Figure 7 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 operation of this flyback converter circuit during its operating cycle is similar to... Figure 6 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 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 absorption capacitor C3 is cut off.

[0071] In some embodiments, such as Figure 8As shown, the flyback converter circuit also includes a third diode D3. The absorption circuit is connected in series with the third diode D3 and then in parallel with the third switch Q3. When the third switch Q3 is turned on, the third diode D3 prevents the charge in the absorption capacitor from discharging through the third switch Q3. After the third switch Q3 is turned off, the third diode D3 forms part of the absorption clamping circuit. For example, the cathode of the third diode D3 is connected to the busbar, and the anode is connected to the low-potential terminal P31 of the absorption circuit. Alternatively, the cathode of the third diode D3 can be connected to the high-potential terminal P32, and the anode can be connected to the cathode of the first diode D1 (not shown in the figure). As mentioned earlier, when the bus sampling voltage is less than the threshold voltage, the 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 absorption capacitor C3 discharges through the absorption resistor R1. Otherwise, if the third diode D3 is not present, at the moment the third switch Q3 is controlled to conduct, the absorption capacitor C3 is short-circuited due to the conduction of the third switch Q3. The voltage of the absorption capacitor C3 is instantaneously applied to the third switch Q3, generating a momentary high voltage, which will damage the third switch Q3. Similarly, Figure 7 The flyback converter circuit in the circuit may also include a third diode D3, which will not be elaborated here.

[0072] Those skilled in the art will understand that, without conflict, the above-mentioned preferred solutions can be freely combined and superimposed.

[0073] Those skilled in the art will understand that, without conflict, the above-mentioned preferred solutions can be freely combined and superimposed.

[0074] 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 third switch, voltage comparison circuit, and absorption circuit, wherein the absorption circuit includes an absorption capacitor and an 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 anode of the first diode is connected to the first end of the primary coil, and the cathode is connected to the busbar; The second diode and the third switch are connected in series between the second end of the primary coil and ground; the third switch is connected in parallel with the absorption circuit, in which the absorption capacitor and the absorption resistor are connected in parallel; The voltage comparison circuit compares the bus sampled voltage with the threshold voltage. When the bus sampling voltage is greater than the threshold voltage, the voltage comparison circuit controls the third switch to turn on, so that the second diode and the third switch form a clamping circuit for the primary coil, and the current direction in the clamping circuit is from the anode and cathode of the second diode to the second end of the primary coil, and the third switch short-circuits the 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 second diode and the absorption circuit to form a clamping absorption circuit for the primary coil.

2. The flyback converter circuit according to claim 1, characterized in that, It also includes a third diode. The 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 absorption capacitor from discharging through the third switch. After the third switch is turned off, the third diode constitutes part of the absorption clamping circuit.

3. The flyback converter circuit according to claim 1, characterized in that, It also includes a control unit, When the output voltage of the flyback converter circuit is adjusted to a new voltage value, the control unit updates the threshold voltage and outputs the updated threshold voltage to the voltage comparison circuit.

4. The flyback converter circuit according to claim 3, characterized in that, The secondary winding of the transformer outputs the output voltage through a rectifier diode, and 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); Wherein, 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 the sampling coefficient, with a value range of (0, 1).

5. The flyback converter circuit according to claim 3, characterized in that, The secondary winding of the transformer outputs the output voltage through a rectifier diode, and 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); Wherein, 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 coils of the transformer; and k is the sampling coefficient, with a value range of (0, 1).

6. 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 sampled voltage with the threshold voltage. When the bus sampling voltage is greater than the threshold voltage, the voltage comparison circuit controls the third switch to turn on, so that the second diode and the third switch form a clamping circuit for the primary coil, and the current direction in the clamping circuit is from the anode and cathode of the second diode to the second end of the primary coil, and the third switch short-circuits the 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 second diode and the absorption circuit to form a clamping absorption circuit for the primary coil.

7. The control method as described in claim 6, characterized in that, The flyback converter circuit further includes a control unit, and 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 and outputs the updated threshold voltage to the voltage comparison circuit.

8. The control method as described in claim 7, characterized in that, The secondary winding of the transformer outputs the output voltage through a rectifier diode, and 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); Wherein, Vth, Vo, and Vd are the threshold voltage, the output voltage, and the voltage drop of the rectifier diode, respectively, and n is the turns ratio of the primary and secondary coils of the transformer.

9. The control method according to claim 7, characterized in that, The secondary winding of the transformer outputs the output voltage through a rectifier diode, and 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); Wherein, 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 coils of the transformer; and k is the sampling coefficient, with a value range of (0, 1).

10. A flyback converter circuit, comprising a first switch, a second switch, a first diode, and a second diode, characterized in that, Also includes: The third switch, voltage comparison circuit, and absorption circuit, wherein the absorption circuit includes an absorption capacitor and an 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 cathode of the second diode is connected to the second terminal of the primary coil, and the anode is grounded; The first diode and the third switch are connected in series between the first end of the primary coil and the busbar; the third switch is connected in parallel with the absorption circuit, in which the absorption capacitor and the absorption resistor are connected in parallel; The voltage comparison circuit compares the bus sampled voltage with the threshold voltage. When the bus sampling voltage is greater than the threshold voltage, the voltage comparison circuit controls the third switch to turn on, thereby forming a clamping circuit for the primary coil with the first diode and the third switch. The current direction in the clamping circuit is from the anode of the first diode, the cathode of the first diode to the bus, and the third switch short-circuits the 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 absorption circuit to form a clamping absorption circuit for the primary coil.

11. The flyback converter circuit according to claim 10, characterized in that, It also includes a third diode. The 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 absorption capacitor from discharging through the third switch. After the third switch is turned off, the third diode constitutes part of the absorption clamping circuit.

12. The flyback converter circuit according to claim 10, characterized in that, It also includes a control unit, When the output voltage of the flyback converter circuit is adjusted to a new voltage value, the control unit updates the threshold voltage and outputs the updated threshold voltage to the voltage comparison circuit.

13. The flyback converter circuit according to claim 12, characterized in that, The secondary winding of the transformer outputs the output voltage through a rectifier diode, and 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); Wherein, 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 the sampling coefficient, with a value range of (0, 1).

14. The flyback converter circuit according to claim 12, characterized in that, The secondary winding of the transformer outputs the output voltage through a rectifier diode, and 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); Wherein, 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 coils of the transformer; and k is the sampling coefficient, with a value range of (0, 1).

15. A control method for a flyback converter circuit, characterized in that, Using the flyback converter circuit as described in claim 10, the control method includes the following steps: The voltage comparison circuit compares the bus sampled voltage with the threshold voltage. When the bus sampling voltage is greater than the threshold voltage, the voltage comparison circuit controls the third switch to turn on, thereby forming a clamping circuit for the primary coil with the first diode and the third switch. The current direction in the clamping circuit is from the anode of the first diode, the cathode of the first diode to the bus, and the third switch short-circuits the 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 absorption circuit to form a clamping absorption circuit for the primary coil.

16. The control method according to claim 15, characterized in that, The flyback converter circuit further includes a control unit, and 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 and outputs the updated threshold voltage to the voltage comparison circuit.

17. The control method according to claim 16, characterized in that, The secondary winding of the transformer outputs the output voltage through a rectifier diode, and 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); Wherein, 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 the sampling coefficient, with a value range of (0, 1).

18. The control method according to claim 16, characterized in that, The secondary winding of the transformer outputs the output voltage through a rectifier diode, and 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); Wherein, 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 coils of the transformer; and k is the sampling coefficient, with a value range of (0, 1).

19. A flyback converter, comprising a transformer, characterized in that, It also includes the flyback converter circuit as described in any one of claims 1-5 and 10-14.

20. A servo motor driver, comprising a transformer, characterized in that, It also includes the flyback converter circuit as described in any one of claims 1-5 and 10-14.

21. A servo motor, characterized in that, Includes the servo motor driver as described in claim 20.

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