Brushless direct current motor braking circuit
By setting a load branch in the switching branch of the brushless DC motor and controlling the on/off state of the load switch tube, the problems of large weight and high cost in the braking of brushless DC motors are solved, achieving efficient braking and good compatibility of brushless motors.
Patent Information
- Application Number
- CN202423080948.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2024-12-12
- Publication Date
- 2025-11-28
- Estimated Expiration
- 2034-12-12
AI Technical Summary
Existing brushless DC motors suffer from problems of large weight and size when braking via counterweights, and high cost when braking via brake pads.
Design a brushless DC motor braking circuit, including three parallel switch branches, each consisting of an upper switch transistor and a lower switch transistor. By setting a load branch at the connection end of the upper and lower switch transistors, the motor braking is achieved by controlling the on and off of the load switch transistor, thus avoiding the need to add brake pads and counterweights.
It achieves braking of the brushless motor without increasing size and cost, while also providing uniform descent, and achieves good compatibility through PID control and adjustable resistors.
Smart Images
Figure CN223613245U_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The utility model relates to brushless motor braking technical field, concretely relates to a kind of brushless direct current motor braking circuit. BACKGROUND
[0002] Brushless DC motor has been widely used in driving power field due to its advantages of high efficiency, fast speed, good durability, long life, high reliability, low electrical noise and low interference.
[0003] At present, in the application product of brushless DC motor, for example, in the elevator in vertical shaft, braking deceleration can be carried out by increasing counterweight block;Or in the car, deceleration can be carried out by brake pad.And the way of braking by counterweight block has the problem of increasing product weight and volume, which is not conducive to the application of volume limited scene;In addition, the brake pad is easy to wear and the maintenance cost is high. UTILITY MODEL CONTENTS
[0004] In view of the deficiencies of the background art, the utility model provides a kind of brushless DC motor braking circuit, and the technical problems to be solved are that the existing brushless DC motor exists the problems of large weight and large volume by counterweight block in application, and exists the problem of high cost by brake pad.
[0005] To solve the above technical problems, the utility model provides the following technical scheme: a kind of brushless DC motor braking circuit, including three parallel switch branches, each switch branch includes the upper switch tube and the lower switch tube in series, the input end of the upper switch tube of the switch branch is used to access power supply, and the output end of the lower switch tube of all switch branches is connected to analog ground;
[0006] The connection end of the upper switch tube and the lower switch tube of each switch branch is respectively connected with load branch, and the load branch includes load switch tube and load resistance in series, the input end of the load switch tube is electrically connected with the connection end, and the output end of the load switch tube is connected to analog ground through load resistance.
[0007] In certain embodiments, the upper switch tube and the lower switch tube are both NMOS tubes, the drain of the NMOS tube is the input end of the switch tube, and the source of the NMOS tube is the output end of the switch tube.
[0008] In certain embodiments, the load switch tube is an NMOS tube, the drain of the NMOS tube is the input end of the load switch tube, and the source of the NMOS tube is the output end of the load switch tube.
[0009] In certain embodiments, the resistance of the load resistance is adjustable.
[0010] In certain embodiments, the utility model further include control unit, first isolation unit, first drive unit, second isolation unit and three second drive units;
[0011] The control unit is electrically connected with the first drive unit through the first isolation unit, inputs the first control signal of controlling upper and lower switch tubes to the first isolation unit, and the first drive unit inputs corresponding switch control signals to the upper and lower switch tubes based on the first isolation control signal output by the first isolation unit;
[0012] The control unit is electrically connected with three second drive units through the second isolation unit, inputs the second control signal of controlling load switch tubes to the second isolation unit, and three second drive units input load switch control signals to three load switch tubes based on the second isolation control signal output by the second isolation unit.
[0013] In certain embodiments, the first isolation unit includes isolation chip U5 with model CA-IS3760LN, the first isolation chip No. and sixteen No. are used to input working voltage, the second isolation chip U5 No. three No. four No. five No. six No. and seven No. are electrically connected with the control unit respectively for inputting the first control signal, the eighth No. of the isolation chip U5 connects digital ground, the ninth No. of the isolation chip U5 connects analog ground, the tenth No. of the isolation chip U5 eleven No. twelve No. thirteen No. fourteen No. and fifteen No. are used to output isolation control signal.
[0014] In certain embodiments, the first drive unit includes first drive chip U6 with model FD6288, the first drive chip U6 No. two No. three No. four No. five and six No. are electrically connected with the fifteenth No. of isolation chip U5 fourteen No. thirteen No. twelve No. eleven No. and tenth No. respectively;
[0015] The seventh No. of the first drive chip U6 is used to input the working voltage, and is connected with analog ground through capacitor C28 and capacitor C29 respectively, and the eighth No. of first drive chip U6 connects analog ground;
[0016] Also included are diode D19, diode D20 and diode D21, the anode of diode D19 is respectively electrically connected with the anode of diode D20 and the anode of diode D21, for inputting working voltage; the cathode of diode D19 is respectively electrically connected with the positive electrode of capacitor E26 and the twenty number pin of first driving chip U6, the negative electrode of capacitor E26 is electrically connected with the eighteen number pin of first driving chip U6; the cathode of diode D20 is respectively electrically connected with the positive electrode of capacitor E27 and the seventeen number pin of first driving chip U6, the negative electrode of capacitor E27 is electrically connected with the fifteen number pin of first driving chip U6; the cathode of diode D21 is respectively electrically connected with the positive electrode of capacitor E28 and the fourteen number pin of first driving chip U6, the negative electrode of capacitor E28 is electrically connected with the twelve number pin of first driving chip U6;
[0017] The nineteen number pin, sixteen number pin and thirteen number pin of first driving chip U6 are respectively electrically connected with the control end of three upper switch tubes, the eleven number pin, ten number pin and nine number pin of first driving chip U6 are respectively electrically connected with the control end of three lower switch tubes.
[0018] In certain embodiments, the second isolation unit also includes isolation chip U7 with model number CA-IS3760LN; the control unit is electrically connected with the two number pin, three number pin and four number pin of isolation chip U7;
[0019] The second driving unit includes second driving chip U8 with model number ZXGD3009DY, the two number pin of three second driving chip U8 is respectively electrically connected with the fifteen number pin, fourteen number pin and thirteen number pin of isolation chip U7, the one number pin of second driving chip U8 is used for inputting working voltage, and is connected with analog ground through capacitor C30, the three number pin of second driving chip U8 is connected with analog ground, the six number pin of second driving chip U8 is electrically connected with the control end of load switch tube, and load switch control signal is inputted to the control end of load switch tube.
[0020] In certain embodiments, the output end of lower switch tube of each switch branch is respectively electrically connected with one end of sampling resistor, the other end of sampling resistor is connected with ground;
[0021] Also included are isolation differential operational amplifier unit and secondary operational amplifier unit, the isolation differential operational amplifier unit is electrically connected with the sampling resistor, and the voltage on the sampling resistor is sampled, the input end of secondary operational amplifier unit is electrically connected with the isolation differential operational amplifier unit, and the output end of secondary operational amplifier unit is connected with the control unit.
[0022] In certain embodiments, the control end of each upper switch tube, the control end of each lower switch tube and the control end of each load switch tube are respectively electrically connected with a discharge circuit, the discharge circuit comprising a diode D10 and a resistor R20, the anode of the diode D10 and one end of the resistor R20 being electrically connected with the control end of the corresponding tube, the cathode of the diode D10 and the other end of the resistor R20 being electrically connected;
[0023] The anode of the diode D10 is also electrically connected with the output end of the corresponding switch tube through a resistor R100.
[0024] The utility model has the beneficial effects compared with prior art: firstly, the connection ends of the upper switch tubes and the lower switch tubes of the three switch branches are respectively electrically connected with the three windings of the brushless DC motor, and the utility model sets up the load branch at the connection ends of the upper switch tubes and the lower switch tubes, and controls whether the load resistor is connected by controlling the on-off of the load switch tube, thereby realizing the braking of the brushless motor, and without increasing the brake pad and the counterweight, the utility model has small occupied area and low cost.
[0025] Secondly, the on-off of the load switch tube can be controlled by using the PID regulation mode, and the uniform speed descending can be realized.
[0026] Finally, the resistance size in the load branch can be adjusted according to actual demand by setting the digital potentiometer, and the utility model has good compatibility. BRIEF DESCRIPTION OF DRAWINGS
[0027] Figure 1 It is the circuit diagram of the three switch branches and the three load branches of the utility model and the brushless motor.
[0028] Figure 2 It is the structural schematic view of the control unit, the first isolation unit, the first driving unit, the second isolation unit, the second driving unit, the isolation differential operational amplifier unit and the two-stage operational amplifier unit.
[0029] Figure 3 It is the circuit diagram of the first isolation unit and the first driving unit in the embodiment.
[0030] Figure 4 It is the circuit diagram of the second isolation unit in the embodiment.
[0031] Figure 5 It is the circuit diagram of the second driving unit in the embodiment.
[0032] Figure 6 It is the circuit diagram of the discharge circuit and the switch tube in the embodiment. DETAILED DESCRIPTION
[0033] The present invention will now be described in further detail with reference to the accompanying drawings. These drawings are simplified schematic diagrams, illustrating only the basic structure of the present invention, and therefore only show the components relevant to the present invention.
[0034] To address the shortcomings of using counterweights and brake pads for brushless motor braking, such as Figure 1 As shown, this embodiment provides a brushless DC motor braking circuit, including three parallel switching branches 1. Each switching branch 1 includes an upper switching transistor and a lower switching transistor connected in series. The input terminal of the upper switching transistor of the switching branch 1 is used to connect to the power supply VM, and the output terminal of the lower switching transistor of all switching branches 1 is connected to analog ground. In addition, in order to ensure the stability of the power supply VM, a filter capacitor can be set at the input terminal of each switching branch 1 for filtering. The number of filter capacitors is not limited. When the number of filter capacitors is greater than 1, all filter capacitors are set in parallel, that is, one end of all filter capacitors is electrically connected to the input terminal of the corresponding switching branch, and the other end of all filter capacitors is grounded.
[0035] by Figure 1 Taking the leftmost switch branch 1 as an example, the switch branch 1 includes an upper switch HU and a lower switch LU connected in series;
[0036] exist Figure 1 In the middle, the upper and lower switch tubes of each switch branch 1 are connected to load branch 2 respectively. The load branch 2 includes a load switch tube and a load resistor connected in series. The input terminal of the load switch tube is electrically connected to the connection terminal of the upper and lower switch tubes, and the output terminal of the load switch tube is connected to analog ground through the load resistor.
[0037] Similarly, with Figure 1 Taking the leftmost load branch 2 as an example, this load branch 2 includes a load switch LU1 and a load resistor RPU.
[0038] In practical use, the connection terminals of the upper and lower switching transistors of the three switching branches 1 of this utility model are respectively used for electrical connection with the three windings of the brushless DC motor. Figure 1 Nodes U, V, and W are used to connect to the three windings of the brushless DC motor. This invention sets up a load branch 2 at the connection end of the upper and lower switching tubes. By controlling the on / off state of the load switching tube, the load resistor can be controlled to achieve braking of the brushless motor. Moreover, there is no need to add brake pads and counterweights, so it occupies a small area and has low cost.
[0039] Specifically, in this embodiment, the upper and lower switching transistors in each switching branch 1 are NMOS transistors. The drain of the NMOS transistor is the input terminal of the switching transistor, the source of the NMOS transistor is the output terminal of the switching transistor, and the gate of the NMOS transistor is the control terminal of the switching transistor.
[0040] In addition, in this embodiment, the load switch in each load branch 2 is an NMOS transistor, the drain of the NMOS transistor is the input terminal of the load switch transistor, the source of the NMOS transistor is the output terminal of the load switch transistor, and the gate of the NMOS transistor is the control terminal of the load switch transistor.
[0041] In addition, in this embodiment, the resistance value of the load resistor is adjustable, and the load resistor can be a digital potentiometer. In actual use, the resistance value in load branch 2 can be adjusted according to actual needs by setting the digital potentiometer, offering good compatibility. Furthermore, other models of digital potentiometers can be selected according to actual requirements.
[0042] like Figure 2 As shown, in this embodiment, the present invention also includes a control unit 3, a first isolation unit 4, a first drive unit 5, a second isolation unit 10, and three second drive units 6;
[0043] The control unit 3 is electrically connected to the first drive unit 5 through the first isolation unit 4, and inputs a first control signal to the first isolation unit 5 to control the upper and lower switching transistors. The first drive unit 5 inputs corresponding switching control signals to the upper and lower switching transistors based on the isolation control signal output by the first isolation unit 4. The switching control signals are used to control the on and off of the upper and lower switching transistors.
[0044] The control unit 3 is electrically connected to the three second drive units 6 through the second isolation unit 10, and inputs a second control signal to the second isolation unit 10 to control the load switch transistor. The three second drive units 6 input load switch control signals to the three load switch transistors based on the second isolation control signal output by the second isolation unit 10. The load switch control signal is used to control the on and off of the load switch transistor.
[0045] Specifically, in this embodiment, as Figure 3 As shown, the first isolation unit 4 includes an isolation chip U5 of model CA-IS3760LN. Pins 1 and 16 of the isolation chip are used to input the working voltage. Pins 2, 3, 4, 5, 6, and 7 of the isolation chip U5 are electrically connected to the control unit and are used to input the first control signal. Pin 8 of the isolation chip U5 is connected to digital ground, pin 9 of the isolation chip U5 is connected to analog ground, and pins 10, 11, 12, 13, 14, and 15 of the isolation chip U5 are used to output the isolation control signal.
[0046] exist Figure 3In the configuration, the isolation control signal output from pin 15 of isolation chip U5 corresponds to the first control signal input from pin 2 of isolation chip U5; the isolation control signal output from pin 14 of isolation chip U5 corresponds to the first control signal input from pin 3 of isolation chip U5; the isolation control signal output from pin 13 of isolation chip U5 corresponds to the first control signal input from pin 3 of isolation chip U5; the isolation control signal output from pin 12 of isolation chip U5 corresponds to the first control signal input from pin 5 of isolation chip U5; the isolation control signal output from pin 11 of isolation chip U5 corresponds to the first control signal input from pin 6 of isolation chip U5; and the isolation control signal output from pin 10 of isolation chip U5 corresponds to the first control signal input from pin 7 of isolation chip U5.
[0047] In this embodiment, as Figure 3 As shown, the first driving unit 3 includes a first driving chip U6 of model FD6288. Pins 1, 2, 3, 4, 5 and 6 of the first driving chip U6 are electrically connected to pins 15, 14, 13, 12, 11 and 10 of the isolation chip U5, respectively.
[0048] Pin 7 of the first driver chip U6 is used to input the working voltage and is connected to analog ground through capacitors C28 and C29 respectively. Pin 8 of the first driver chip U6 is connected to analog ground.
[0049] It also includes diodes D19, D20, and D21. The anode of diode D19 is electrically connected to the anodes of diodes D20 and D21, respectively, for inputting the working voltage. The cathode of diode D19 is electrically connected to the positive terminal of capacitor E26 and pin 20 of the first driver chip U6, and the negative terminal of capacitor E26 is electrically connected to pin 18 of the first driver chip U6. The cathode of diode D20 is electrically connected to the positive terminal of capacitor E27 and pin 17 of the first driver chip U6, and the negative terminal of capacitor E27 is electrically connected to pin 15 of the first driver chip U6. The cathode of diode D21 is electrically connected to the positive terminal of capacitor E28 and pin 14 of the first driver chip U6, and the negative terminal of capacitor E28 is electrically connected to pin 12 of the first driver chip U6.
[0050] Pins 19, 16, and 13 of the first driver chip U6 are electrically connected to the control terminals of the three upper switching transistors, respectively. Pins 11, 10, and 9 of the first driver chip U6 are electrically connected to the control terminals of the three lower switching transistors, respectively. Specifically, pins 19 and 11 of the first driver chip U6 are used to control the upper and lower switching transistors of one switching branch; pins 16 and 10 of the first driver chip U6 are used to control the upper and lower switching transistors of another switching branch; and pins 13 and 9 of the first driver chip U6 are used to control the upper and lower switching transistors of the remaining switching branch.
[0051] In this embodiment, as Figure 4 As shown, the second isolation unit 10 also includes an isolation chip U7 of model CA-IS3760LN; the control unit 3 is electrically connected to pins 2, 3 and 4 of the isolation chip U7.
[0052] In this embodiment, as Figure 5 As shown, the second drive unit 6 includes a second drive chip U8 of model ZXGD3009DY. The second pin of the three second drive chips U8 is electrically connected to the fifteenth, fourteenth and thirteenth pins of the isolation chip U7, respectively. The second pin of the second drive chip U8 is electrically connected to the control unit 3. The first pin of the second drive chip U8 is used to input the working voltage and is connected to the analog ground through capacitor C30. The third pin of the second drive chip U8 is connected to the analog ground. The sixth pin of the second drive chip U8 is electrically connected to the control terminal of the load switch transistor and inputs the load switch control signal to the control terminal of the load switch transistor.
[0053] In this embodiment, the operating voltage is 5V.
[0054] In addition, in this embodiment, such as Figure 1 As shown, the output terminal of the lower switching transistor in each switching branch is electrically connected to one end of the sampling resistor RS1, and the other end of the sampling resistor RS1 is grounded. In actual use, overcurrent protection can be achieved by setting the sampling resistor RS1.
[0055] In addition Figure 2 In addition, this utility model also includes an isolation differential operational amplifier unit 7 and a secondary operational amplifier unit 8. The isolation differential operational amplifier unit 7 is electrically connected to the sampling resistor RS1 to sample the voltage on the sampling resistor RS1. The input terminal of the secondary operational amplifier unit 8 is electrically connected to the isolation differential operational amplifier unit 7, and the output terminal of the secondary operational amplifier unit 8 is electrically connected to the control unit 3.
[0056] Specifically, in the embodiment, each of the isolation differential operational amplifier unit 7 and the secondary operational amplifier unit 8 is a prior art circuit, wherein the isolation differential operational amplifier unit 7 can include an operational amplifier chip of model CA-IS1200G, and the secondary operational amplifier unit 8 can include an amplifier chip of model LM358.
[0057] In actual use, when the control unit 3 detects that the current on the sampling resistor RS1 is too large through the isolation differential operational amplifier unit 7 and the secondary operational amplifier unit 8, the corresponding load switch control signal can be output by the second driving unit 6 to brake.
[0058] In the embodiment, the control end of each upper switch tube, the control end of each lower switch tube and the control end of each load switch tube are respectively electrically connected with a discharge circuit 9, so that Figure 1 Taking the leftmost switch branch 1 as an example, as shown in the figure, the discharge circuit 9 includes a diode D10 and a resistor R20, the anode of the diode D10 and one end of the resistor R20 are electrically connected with the control end of the corresponding tube, and the cathode of the diode D10 and the other end of the resistor R20 are electrically connected. Figure 6
[0059] The anode of the diode D10 is also electrically connected with the output end of the corresponding switch tube through a resistor R100.
[0060] According to the above description, relevant personnel can make various changes and modifications without deviating from the technical idea of the utility model. The technical scope of the utility model is not limited to the content of the specification, and must be determined according to the scope of the claims.
Claims
1. A brushless DC motor braking circuit, characterized by, The switch branch includes three parallel switch branches, each of which includes a series connection of an upper switch tube and a lower switch tube, and the input end of the upper switch tube of the switch branch is used for accessing a power supply, and the output end of the lower switch tube of all switch branches is connected to an analog ground; The connection end of the upper switch tube and the lower switch tube of each switch branch is connected with a load branch, and the load branch includes a series connection of a load switch tube and a load resistor, the input end of the load switch tube is electrically connected with the connection end, and the output end of the load switch tube is connected to the analog ground through the load resistor.
2. A brushless DC motor braking circuit according to claim 1, wherein, The upper switch tube and the lower switch tube are both NMOS tubes, the drain of the NMOS tube is the input end of the switch tube, and the source of the NMOS tube is the output end of the switch tube.
3. A brushless DC motor braking circuit according to claim 1, wherein, The load switch tube is an NMOS tube, the drain of the NMOS tube is the input end of the load switch tube, and the source of the NMOS tube is the output end of the load switch tube.
4. A brushless DC motor braking circuit according to claim 1, wherein, The resistance of the load resistor is adjustable.
5. A brushless DC motor braking circuit according to claim 1, wherein, The control unit, the first isolation unit, the first driving unit, the second isolation unit and the three second driving units are further included. The control unit is electrically connected with the first driving unit through the first isolation unit, inputs a first control signal for controlling the upper switch tube and the lower switch tube to the first isolation unit, and inputs corresponding switch control signals to the upper switch tube and the lower switch tube based on the first isolation control signal output by the first isolation unit. The control unit is electrically connected with the three second driving units through the second isolation unit, inputs a second control signal for controlling the load switch tube to the second isolation unit, and inputs load switch control signals to the three load switch tubes based on the second isolation control signal output by the second isolation unit.
6. A brushless DC motor braking circuit as claimed in claim 5, wherein, The first isolation unit includes an isolation chip U5 with a model number of CA-IS3760LN, the first pin and the sixteenth pin of the isolation chip are used for inputting a working voltage, the second pin, the third pin, the fourth pin, the fifth pin, the sixth pin and the seventh pin of the isolation chip U5 are electrically connected with the control unit and used for inputting the first control signal, the eighth pin of the isolation chip U5 is connected to a digital ground, the ninth pin of the isolation chip U5 is connected to an analog ground, and the tenth pin, the eleventh pin, the twelfth pin, the thirteenth pin, the fourteenth pin and the fifteenth pin of the isolation chip U5 are used for outputting an isolation control signal.
7. A brushless DC motor braking circuit as claimed in claim 6, wherein, The first driving unit includes a first driving chip U6 with a model number of FD6288, the first pin, the second pin, the third pin, the fourth pin, the fifth pin and the sixth pin of the first driving chip U6 are electrically connected with the fifteenth pin, the fourteenth pin, the thirteenth pin, the twelfth pin, the eleventh pin and the tenth pin of the isolation chip U5, respectively; The seventh pin of the first driving chip U6 is used for inputting the working voltage and is connected to the analog ground through the capacitor C28 and the capacitor C29, respectively, and the eighth pin of the first driving chip U6 is connected to the analog ground; Also includes diode D19, diode D20 and diode D21, the anode of diode D19 is respectively connected with the anode of diode D20 and the anode of diode D21, for input working voltage;The cathode of diode D19 is respectively connected with the positive electrode of capacitor E26 and the twenty number pin of first drive chip U6, the negative electrode of capacitor E26 is connected with the eighteen number pin of first drive chip U6;The cathode of diode D20 is respectively connected with the positive electrode of capacitor E27 and the seventeen number pin of first drive chip U6, the negative electrode of capacitor E27 is connected with the fifteen number pin of first drive chip U6;The cathode of diode D21 is respectively connected with the positive electrode of capacitor E28 and the fourteen number pin of first drive chip U6, the negative electrode of capacitor E28 is connected with the twelve number pin of first drive chip U6; The nineteen number pin, sixteen number pin and thirteen number pin of the first drive chip U6 are respectively connected with the control end of three upper switch tubes, and the eleven number pin, ten number pin and nine number pin of the first drive chip U6 are respectively connected with the control end of three lower switch tubes.
8. A brushless DC motor braking circuit as claimed in claim 5, wherein, The second isolation unit also includes isolation chip U7 with model CA-IS3760LN;The control unit is connected with the second number pin, third number pin and fourth number pin of the isolation chip U7; The second drive unit includes second drive chip U8 with model ZXGD3009DY, and the second number pin of three second drive chips U8 is respectively connected with the fifteen number pin, fourteen number pin and thirteen number pin of the isolation chip U7, the first number pin of the second drive chip U8 is used for input working voltage, and is connected with analog ground through capacitor C30, the third number pin of the second drive chip U8 is connected with analog ground, and the sixth number pin of the second drive chip U8 is connected with the control end of load switch tube, and load switch control signal is input to the control end of load switch tube.
9. A brushless DC motor braking circuit as claimed in claim 5, wherein, The output end of the lower switch tube of each switch branch is respectively connected with one end of sampling resistor, and the other end of the sampling resistor is connected with ground; Also includes isolation differential operational amplifier unit and secondary operational amplifier unit, the isolation differential operational amplifier unit is connected with the sampling resistor, and the voltage on the sampling resistor is sampled, and the input end of the secondary operational amplifier unit is connected with the isolation differential operational amplifier unit, and the output end of the secondary operational amplifier unit is connected with the control unit.
10. A brushless DC motor braking circuit as claimed in claim 1, wherein, The control end of each upper switch tube, the control end of lower switch tube and the control end of load switch tube are respectively connected with discharge circuit, and the discharge circuit includes diode D10 and resistor R20, the anode of diode D10 and one end of resistor R20 are connected with the control end of corresponding tube, and the cathode of diode D10 and the other end of resistor R20 are connected. The anode of diode D10 is also connected with the output end of corresponding switch tube through resistor R100.