Double-loop flyback power supply control circuit

Abstract

The utility model discloses a double-loop flyback power supply control circuit, which comprises a transformer T1, a primary side controller U1, a rectification controller U2, a protocol controller U0, an optical coupler OC1 and an optical coupler OC2, the primary side controller U1 is electrically connected with the primary side of the transformer T1, the rectification controller U2 is electrically connected with the secondary side of the transformer T1, and the protocol controller U0 is electrically connected with the rectification controller U2; the input end of the optical coupler OC1 is electrically connected with the secondary side of the transformer T1, and the output end of the optical coupler OC1 is electrically connected with the primary side controller U1 so as to transmit error signals of primary and secondary side voltages to the primary side controller U1; the input end of the rectifier controller U2 is electrically connected with the rectifier controller U0, the input end of the optocoupler OC2 is electrically connected with the protocol controller U0, the output end of the optocoupler OC2 is electrically connected with the primary side controller U1, and the protocol controller U0 can control the working states of the rectifier controller U2 and the optocoupler OC2 by detecting the level change of the signal end of the protocol controller U0, so that the primary side controller U1 is controlled to enter / exit a standby mode.

Description

Technical Field

[0001] The utility model relates to the technical field of power supply control circuits, in particular to a dual-loop flyback power supply control circuit. Background Art

[0002] As energy efficiency standards become increasingly stringent, power supply products are developing in two directions: higher conversion efficiency and lower standby power consumption. Commonly used switching power supplies use closed-loop control to achieve stable voltage output, usually using optocouplers to transmit the primary-secondary voltage error signal to the primary controller. The typical charger application schematic with PD protocol is shown in the attached figure of the manual. Figure 1 In order to obtain a stable error voltage signal on the primary side, the optocoupler OC1 works in the linear region, that is, a certain current always flows through the optocoupler OC1, which will generate a certain amount of power consumption, making it difficult to achieve low standby power consumption. In order to achieve low standby power consumption, it is necessary to cut off the current in the loop optocoupler OC1. At this time, the output error voltage signal cannot be transmitted to the primary side controller U1 through the optocoupler OC1, and the circuit is in an open-loop state, and the output voltage cannot be stabilized.

[0003] When the existing technical solution realizes low standby power consumption, it usually monitors the output voltage through the secondary synchronous rectification controller U2 after the current of the loop optocoupler OC1 is cut off. When the output voltage is too low, the synchronous rectifier Q2 is short-circuited for a short time through the synchronous rectification controller U2. At this time, the output voltage is added to the secondary winding of the transformer, and the primary auxiliary winding senses a voltage signal related to the output voltage amplitude ratio. After the primary controller U1 detects the signal, it turns on the primary power switch Q1 to supplement the secondary energy. After the existing technical solution enters the standby working state, the stabilization of the secondary output voltage is achieved through the cooperation of the synchronous rectification controller U2 and the primary controller U1. In the standby mode, both controllers cannot be completely turned off (the synchronous rectification controller U2 and the primary controller U1 need to detect the output voltage and the primary auxiliary winding voltage in real time respectively), and the power consumption of the controller cannot be optimized. In addition, the switching logic of the existing technical solution from the normal working mode to the standby working mode can only be implemented through the primary side controller U1, and the primary side controller U1 cannot directly receive the secondary side related signals at this stage, resulting in complex detection and switching logic of the primary side controller U1 and great difficulty in implementation. Utility Model Content

[0004] The purpose of the utility model is to solve at least one of the technical problems existing in the prior art and to provide a dual-loop flyback power supply control circuit which can simplify the switching logic from normal mode to standby mode and reduce the power consumption of the controller after entering the standby mode.

[0005] According to the dual-loop flyback power supply control circuit of the embodiment of the utility model, it includes a transformer T1, a primary side controller U1, a rectifier controller U2, a protocol controller U0, an optocoupler OC1 and an optocoupler OC2, the primary side controller U1 is electrically connected to the primary side of the transformer T1, the rectifier controller U2 is electrically connected to the secondary side of the transformer T1, and the protocol controller U0 is electrically connected to the rectifier controller U2; the input end of the optocoupler OC1 is electrically connected to the secondary side of the transformer T1, and the output end of the optocoupler OC1 is electrically connected to the primary side controller U1 to transmit the error signal of the primary-secondary side voltage to the primary side controller U1; the input end of the optocoupler OC2 is electrically connected to the protocol controller U0, and the output end of the optocoupler OC2 is electrically connected to the primary side controller U1, and the protocol controller U0 can control the working state of the rectifier controller U2 and the optocoupler OC2 by detecting the level change of its signal end, thereby controlling the primary side controller U1 to enter / exit standby mode.

[0006] According to some embodiments of the utility model, the protocol controller U0 includes a signal detection module for detecting the level conversion of the signal end of the protocol controller U0. After the protocol controller U0 enters the standby mode, the signal detection module remains turned on; the primary side controller U1 includes a SLEEP pin detection module for detecting the level change of the output end of the optocoupler OC2. After the primary side controller U1 enters the standby mode, the SLEEP pin detection module remains turned on.

[0007] According to some embodiments of the present invention, it also includes a switch tube Q1 and a switch tube Q2, the switch tube Q1 is electrically connected to the primary side of the transformer T1, and the primary side controller U1 is electrically connected to the switch tube Q1 to control the on and off of the switch tube Q1; the switch tube Q2 is electrically connected to the secondary side of the transformer T1, and the rectifier controller U2 is electrically connected to the switch tube Q2 to control the on and off of the switch tube Q2.

[0008] According to some embodiments of the present invention, a switch tube Q3 is further included. The protocol controller U0 is electrically connected to the switch tube Q3 to control the on and off of the switch tube Q3. The switch tube Q3 is electrically connected to the secondary side of the transformer to output voltage.

[0009] According to some embodiments of the present invention, the primary side controller U1 is a primary side control IC, the rectifier controller U2 is a rectifier control IC, the protocol controller U0 is a PD protocol IC, the primary side control IC includes a SLEEP terminal electrically connected to the output end of the optocoupler OC2, a COMP terminal electrically connected to the output end of the optocoupler OC1, a CS terminal electrically connected to the second end of the switch tube Q1, and a GATE terminal electrically connected to the first end of the switch tube Q1. The rectifier control IC includes an EN terminal and a GATE terminal electrically connected to the first end of the switch tube Q2. The PD protocol IC includes a GPIO terminal electrically connected to the EN terminal of the rectifier control IC, an OPTO terminal electrically connected to the input end of the optocoupler OC1, a SLEEP terminal electrically connected to the input end of the optocoupler OC2, a VG terminal electrically connected to the control end of the switch tube Q3, and a CC signal terminal for detecting level changes.

[0010] According to some embodiments of the present invention, a capacitor Co is further included, one end of the capacitor Co is electrically connected to the switch tube Q2, and the other end of the capacitor Co is electrically connected to the secondary side of the transformer T1.

[0011] According to some embodiments of the present utility model, the switch tube Q1, the switch tube Q2 and the switch tube Q3 are MOS tubes respectively, the gate of the switch tube Q1 is electrically connected to the GATE terminal of the primary control IC, the source of the switch tube Q1 is electrically connected to the CS terminal of the primary control IC, and the drain of the switch tube Q1 is electrically connected to the primary side of the transformer T1; the gate of the switch tube Q2 is electrically connected to the GATE terminal of the rectifier control IC, the source of the switch tube Q2 is electrically connected to one end of the capacitor Co, and the drain of the switch tube Q2 is electrically connected to an output end of the secondary side of the transformer T1; the drain of the switch tube Q3 is electrically connected to the other output end of the secondary side of the transformer T1 and the other end of the capacitor Co respectively, the gate of the switch tube Q3 is electrically connected to the VG terminal of the PD protocol IC, and the source of the switch tube Q3 outputs voltage.

[0012] According to some embodiments of the present invention, the inductor L DM , capacitors C1 and C2, inductor L DM One end of the primary side of the transformer T1 and one end of the capacitor C2 are electrically connected, and the other end of the capacitor C2 is electrically connected to one end of the capacitor C1 and the switch tube Q1, and the other end of the capacitor C1 is electrically connected to the inductor L DM The other end is electrically connected.

[0013] According to some embodiments of the present invention, a rectifier module is further included, wherein the rectifier module includes a diode D1, a diode D2, a diode D3 and a diode D4, wherein the cathode of the diode D1 and the cathode of the diode D4 are connected to the inductor L DMThe other end of the diode D1 is electrically connected to the other end of the power supply, the anode of the diode D1 and the cathode of the diode D2 are electrically connected to one end of the power supply respectively, the cathode of the diode D3 and the anode of the diode D4 are electrically connected to the other end of the power supply respectively, and the anode of the diode D2 and the anode of the diode D3 are grounded respectively.

[0014] According to the dual-loop flyback power supply control circuit of the embodiment of the utility model, at least the following beneficial effects are achieved: the protocol controller U0 is electrically connected to the rectifier controller U2, the optocoupler OC1 and the optocoupler OC2 respectively, and the protocol controller U0 can control the working states of the rectifier controller U2 and the optocoupler OC2 by detecting the level change of its signal end, thereby controlling the primary controller U1 to enter / exit the standby mode; for example, after the level of the signal end of the protocol controller U0 is converted for the first time, the protocol controller U0 enters the standby mode, and at the same time controls the rectifier controller U2 to turn off, controls the optocoupler OC2 to turn on to control the primary controller U1 to enter the standby mode, and then disconnects the optocoupler OC1; after the level of the signal end of the protocol controller U0 is converted for the second time, the protocol controller U0 exits the standby mode, and controls the optocoupler OC2 to turn on to control the primary controller U1 to exit the standby mode, and at the same time controls the rectifier controller U2 to turn on. After the primary controller U1 enters the standby mode, the output voltage slowly drops from Vt0 (usually around 5V). When the output voltage drops to a certain threshold value Vt2, the protocol controller U0 turns on the optocoupler OC2, and the collector voltage of the optocoupler OC2 is pulled down. When the primary controller U1 detects that the collector voltage of the optocoupler OC2 is lower than a certain threshold value Vt3, the primary controller U1 drives to send a pulse, and the secondary output voltage rises to higher than Vt2. This cycle repeats. In the standby mode, the output voltage is maintained at the center value Vt2. Since the optocoupler OC2 is in the switching mode and the turn-on duty cycle is very low, the standby power consumption is reduced. That is, the optocoupler OC1 in this circuit can transmit the error signal of the primary and secondary voltages to the primary controller U1. The optocoupler OC2 is used to control the entry / exit of the standby mode and to achieve output voltage regulation after entering the standby mode, which simplifies the switching logic of entering / exiting the standby mode, and after the protocol controller U0 enters the standby mode, the rectifier controller U2 can be completely turned off to minimize power consumption.

[0015] Additional aspects and advantages of the present invention will be given in part in the following description, and in part will become apparent from the following description, or will be learned through the practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The specific implementation of the utility model is further described below in conjunction with the accompanying drawings;

[0017] Figure 1 It is a schematic diagram of a flyback power supply control circuit in the prior art;

[0018] Figure 2It is the schematic diagram of the dual-loop flyback power supply control circuit;

[0019] Figure 3 It is the logic and working sequence of entering the standby mode;

[0020] Figure 4 It is the standby mode exit logic and normal mode working timing. DETAILED DESCRIPTION

[0021] This section will describe in detail the specific embodiments of the utility model. The preferred embodiments of the utility model are shown in the accompanying drawings. The purpose of the accompanying drawings is to supplement the description of the text part of the specification with graphics, so that people can intuitively and vividly understand each technical feature and the overall technical solution of the utility model, but it cannot be understood as a limitation on the protection scope of the utility model.

[0022] In the description of the present invention, it should be understood that descriptions involving orientation, such as up, down, front, back, left, right, etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0023] In the description of the present utility model, "several" means one or more, "more" means more than two, "greater than", "less than", "exceed" etc. are understood to exclude the number itself, and "above", "below", "within" etc. are understood to include the number itself. If there is a description of "first" or "second", it is only used for the purpose of distinguishing the technical features, and cannot be understood as indicating or implying the relative importance or implicitly indicating the number of the indicated technical features or implicitly indicating the order of the indicated technical features.

[0024] Reference Figures 2 to 4 The utility model discloses a dual-loop flyback power supply control circuit, including a transformer T1, a primary side controller U1, a rectifier controller U2, a protocol controller U0, an optocoupler OC1 and an optocoupler OC2, wherein the primary side controller U1 is electrically connected to the primary side of the transformer T1, the rectifier controller U2 is electrically connected to the secondary side of the transformer T1, and the protocol controller U0 is electrically connected to the rectifier controller U2; the input end of the optocoupler OC1 is electrically connected to the secondary side of the transformer T1, and the output end of the optocoupler OC1 is electrically connected to the primary side controller U1 to transmit the error signal of the primary-secondary side voltage to the primary side controller U1; the input end of the optocoupler OC2 is electrically connected to the protocol controller U0, and the output end of the optocoupler OC2 is electrically connected to the primary side controller U1, and the protocol controller U0 can control the working state of the rectifier controller U2 and the optocoupler OC2 by detecting the level change of its signal end, thereby controlling the primary side controller U1 to enter / exit the standby mode.

[0025] like Figure 2 As shown, it also includes switch tube Q1, switch tube Q2, and switch tube Q3. Switch tube Q1 is electrically connected to the primary side of transformer T1, and primary side controller U1 is electrically connected to switch tube Q1 to control the on and off of switch tube Q1; switch tube Q2 is electrically connected to the secondary side of transformer T1, and rectifier controller U2 is electrically connected to switch tube Q2 to control the on and off of switch tube Q2. Protocol controller U0 is electrically connected to switch tube Q3 to control the on and off of switch tube Q3, and switch tube Q3 is electrically connected to the secondary side of the transformer to output voltage. The primary side controller U1 is a primary side control IC, the rectifier controller U2 is a rectifier control IC, and the protocol controller U0 is a PD protocol IC. The primary side control IC includes a SLEEP terminal electrically connected to the output end of the optocoupler OC2, a COMP terminal electrically connected to the output end of the optocoupler OC1, a CS terminal electrically connected to the second end of the switch tube Q1, and a GATE terminal electrically connected to the first end of the switch tube Q1. The rectifier control IC includes an EN terminal and a GATE terminal electrically connected to the first end of the switch tube Q2. The PD protocol IC includes a GPIO terminal electrically connected to the EN terminal of the rectifier control IC, an OPTO terminal electrically connected to the input end of the optocoupler OC1, a SLEEP terminal electrically connected to the input end of the optocoupler OC2, a VG terminal electrically connected to the control end of the switch tube Q3, and a CC signal terminal for detecting level changes.

[0026] like Figure 3After the level of the CC signal end of the PD protocol IC changes from low level to high level, after a delay time t1, the PD protocol IC enters the standby mode (the protocol IC turns off all other modules and only retains the output voltage and CC signal detection module). At this time, the PD protocol IC turns off the synchronous rectification control IC and turns on the optocoupler OC2 for a certain time t2. The collector voltage of the optocoupler OC2 (the SLEEP pin of the primary control IC) is pulled low. When the primary control IC detects that the voltage of its SLEEP pin is lower than a certain threshold Vt1 and the duration is greater than a certain time t3, the primary control IC enters the standby mode (the primary IC turns off all other modules and only retains the SLEEP pin detection module). At this time, the output voltage slowly drops from Vt0 (usually around 5V). When the output voltage drops to a certain threshold value Vt2, the PD protocol IC turns on the optocoupler OC2 for a certain time t4, and the collector voltage of the optocoupler OC2 (the SLEEP pin of the primary control IC) is pulled down. When the primary control IC detects that the voltage of the primary SLEEP pin is lower than a certain threshold value Vt3, the primary control IC drives the pulse with a pulse width of t5, and the secondary output voltage rises to higher than Vt2. This cycle repeats. In standby mode, the output voltage is maintained at the center value Vt2. Since the optocoupler OC2 is in switching mode and the turn-on duty cycle is very low, the standby power consumption is reduced. That is, the optocoupler OC2 in this circuit is used to control the entry / exit of the standby mode and to achieve output voltage regulation after entering the standby mode, which simplifies the switching logic of entering / exiting the standby mode, and after the protocol controller U0 enters the standby mode, the rectifier controller U2 can be completely turned off to minimize power consumption.

[0027] like Figure 4 , is the switching logic for exiting the standby mode and the timing diagram for entering the normal mode. After the protocol IC detects that the CC signal changes from high level to low level after a delay time t6, the protocol IC enters the low power mode (the protocol IC shuts down some modules and only retains the necessary modules). At this time, the protocol IC enables the optocoupler OC1 and turns on the optocoupler OC2 for a certain time t7. The collector voltage of the optocoupler OC2 (the SLEEP pin of the primary control IC) is pulled low. When the primary control IC detects that the voltage of the SLEEP pin of the primary control IC is lower than a certain threshold Vt1 and the duration is greater than a certain time Vt4, the primary control IC enters the normal mode (the primary IC turns on all modules) to establish the output voltage to the normal value Vt0. After a certain delay time t8 after Vt0 is established, the protocol IC enters the normal working mode (the protocol IC turns on all modules). At a certain moment after the protocol IC enables the optocoupler OC1, the protocol IC turns on the rectifier control IC.

[0028] In some embodiments, a capacitor Co is further included, one end of the capacitor Co is electrically connected to the switch tube Q2, and the other end of the capacitor Co is electrically connected to the secondary side of the transformer T1.

[0029] Furthermore, the switch tube Q1, the switch tube Q2 and the switch tube Q3 are MOS tubes respectively, the gate of the switch tube Q1 is electrically connected to the GATE terminal of the primary control IC, the source of the switch tube Q1 is electrically connected to the CS terminal of the primary control IC, and the drain of the switch tube Q1 is electrically connected to the primary side of the transformer T1; the gate of the switch tube Q2 is electrically connected to the GATE terminal of the rectifier control IC, the source of the switch tube Q2 is electrically connected to one end of the capacitor Co, and the drain of the switch tube Q2 is electrically connected to an output terminal of the secondary side of the transformer T1; the drain of the switch tube Q3 is electrically connected to the other output terminal of the secondary side of the transformer T1 and the other end of the capacitor Co respectively, the gate of the switch tube Q3 is electrically connected to the VG terminal of the PD protocol IC, and the source of the switch tube Q3 outputs a voltage. It also includes an inductor L DM , capacitors C1 and C2, inductor L DM One end of the primary side of the transformer T1 and one end of the capacitor C2 are electrically connected, and the other end of the capacitor C2 is electrically connected to one end of the capacitor C1 and the switch tube Q1, and the other end of the capacitor C1 is electrically connected to the inductor L DM The other end of the transformer T1 is electrically connected to form an LC filtering circuit to filter the primary voltage of the transformer T1.

[0030] Furthermore, a rectifier module is included, the rectifier module includes a diode D1, a diode D2, a diode D3 and a diode D4, the cathode of the diode D1 and the cathode of the diode D4 are respectively connected to the inductor L DM The other end of the diode D1 is electrically connected to the other end of the power supply, the anode of the diode D1 and the cathode of the diode D2 are electrically connected to one end of the power supply respectively, the cathode of the diode D3 and the anode of the diode D4 are electrically connected to the other end of the power supply respectively, and the anode of the diode D2 and the anode of the diode D3 are grounded respectively, so as to realize rectification of the AC voltage input on the primary side.

[0031] It is easy for those skilled in the art to understand that the above preferred embodiments can be freely combined and superimposed without conflict.

[0032] The above are only preferred embodiments of the present invention, and are not intended to limit the patent scope of the present invention. All equivalent structural changes made using the contents of the present invention specification and drawings under the utility model concept, or directly or indirectly applied in other related technical fields are included in the patent protection scope of the present invention.

Claims

1. A dual-loop flyback power supply control circuit, characterized in that: include: Transformer T1, primary side controller U1, rectifier controller U2, protocol controller U0, optocoupler OC1 and optocoupler OC2, the primary side controller U1 is electrically connected to the primary side of the transformer T1, the rectifier controller U2 is electrically connected to the secondary side of the transformer T1, and the protocol controller U0 is electrically connected to the rectifier controller U2; the input end of the optocoupler OC1 is electrically connected to the secondary side of the transformer T1, and the output end of the optocoupler OC1 is electrically connected to the primary side controller U1 to transmit the error signal of the primary-secondary side voltage to the primary side controller U1; the input end of the optocoupler OC2 is electrically connected to the protocol controller U0, and the output end of the optocoupler OC2 is electrically connected to the primary side controller U1, and the protocol controller U0 can control the working status of the rectifier controller U2 and the optocoupler OC2 by detecting the level change of its signal end, thereby controlling the primary side controller U1 to enter / exit standby mode.

2. The dual-loop flyback power supply control circuit according to claim 1, characterized in that: The protocol controller U0 includes a signal detection module for detecting level conversion of the signal end of the protocol controller U0. After the protocol controller U0 enters the standby mode, the signal detection module remains turned on; the primary side controller U1 includes a SLEEP pin detection module for detecting level changes at the output end of the optocoupler OC2. After the primary side controller U1 enters the standby mode, the SLEEP pin detection module remains turned on.

3. The dual-loop flyback power supply control circuit according to claim 1, characterized in that: It also includes a switch tube Q1 and a switch tube Q2. The switch tube Q1 is electrically connected to the primary side of the transformer T1, and the primary side controller U1 is electrically connected to the switch tube Q1 to control the on and off of the switch tube Q1; the switch tube Q2 is electrically connected to the secondary side of the transformer T1, and the rectifier controller U2 is electrically connected to the switch tube Q2 to control the on and off of the switch tube Q2.

4. The dual-loop flyback power supply control circuit according to claim 3, characterized in that: It also includes a switch tube Q3. The protocol controller U0 is electrically connected to the switch tube Q3 to control the on and off of the switch tube Q3. The switch tube Q3 is electrically connected to the secondary side of the transformer to output voltage.

5. The dual-loop flyback power supply control circuit according to claim 4, characterized in that: The primary side controller U1 is a primary side control IC, the rectifier controller U2 is a rectifier control IC, and the protocol controller U0 is a PD protocol IC. The primary side control IC includes a SLEEP terminal electrically connected to the output end of the optocoupler OC2, a COMP terminal electrically connected to the output end of the optocoupler OC1, a CS terminal electrically connected to the second end of the switch tube Q1, and a GATE terminal electrically connected to the first end of the switch tube Q1. The rectifier control IC includes an EN terminal and a GATE terminal electrically connected to the first end of the switch tube Q2. The PD protocol IC includes a GPIO terminal electrically connected to the EN terminal of the rectifier control IC, an OPTO terminal electrically connected to the input end of the optocoupler OC1, a SLEEP terminal electrically connected to the input end of the optocoupler OC2, a VG terminal electrically connected to the control end of the switch tube Q3, and a CC signal terminal for detecting level changes.

6. The dual-loop flyback power supply control circuit according to claim 5, characterized in that: It also includes a capacitor Co, one end of which is electrically connected to the switch tube Q2, and the other end of which is electrically connected to the secondary side of the transformer T1.

7. The dual-loop flyback power supply control circuit according to claim 6, characterized in that: The switch tube Q1, the switch tube Q2 and the switch tube Q3 are MOS tubes respectively. The gate of the switch tube Q1 is electrically connected to the GATE terminal of the primary side control IC, the source of the switch tube Q1 is electrically connected to the CS terminal of the primary side control IC, and the drain of the switch tube Q1 is electrically connected to the primary side of the transformer T1; the gate of the switch tube Q2 is electrically connected to the GATE terminal of the rectifier control IC, the source of the switch tube Q2 is electrically connected to one end of the capacitor Co, and the drain of the switch tube Q2 is electrically connected to an output terminal of the secondary side of the transformer T1; the drain of the switch tube Q3 is electrically connected to the other output terminal of the secondary side of the transformer T1 and the other end of the capacitor Co respectively, the gate of the switch tube Q3 is electrically connected to the VG terminal of the PD protocol IC, and the source of the switch tube Q3 outputs voltage.

8. The dual-loop flyback power supply control circuit according to claim 3, characterized in that: Also includes the inductor L DM , capacitors C1 and C2, inductor L DM One end of the primary side of the transformer T1 and one end of the capacitor C2 are electrically connected, and the other end of the capacitor C2 is electrically connected to one end of the capacitor C1 and the switch tube Q1, and the other end of the capacitor C1 is electrically connected to the inductor L DM The other end is electrically connected.

9. The dual-loop flyback power supply control circuit according to claim 8, characterized in that: The rectifier module includes a diode D1, a diode D2, a diode D3 and a diode D4. The cathode of the diode D1 and the cathode of the diode D4 are connected to the inductor L DM The other end of the diode D1 is electrically connected to the other end of the power supply, the anode of the diode D1 and the cathode of the diode D2 are electrically connected to one end of the power supply respectively, the cathode of the diode D3 and the anode of the diode D4 are electrically connected to the other end of the power supply respectively, and the anode of the diode D2 and the anode of the diode D3 are grounded respectively.

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