Capacitive load pre-charging control circuit and system

Abstract

The utility model belongs to the technical field of lithium battery protection boards, and aims to provide a capacitive load pre-charging control circuit and system. The capacitive load pre-charging control circuit comprises a constant current circuit and a charging and discharging control circuit, the constant current circuit comprises a direct current conversion circuit, a switching circuit, a current sampling circuit, a first fly-wheel diode and an energy storage inductor, and the charging and discharging control circuit comprises a charging control circuit and a discharging control circuit. The capacitive load precharge control system includes a capacitive load precharge control circuit. According to the utility model, the current limiting function can be realized through the constant-current circuit, the surge current can be effectively controlled in a limited space, and the effective current limiting function can be realized even in a small space, so that the problem of surge current is avoided, meanwhile, excessive space is not occupied, and the current limiting circuit can be widely applied to the lithium battery protection board.

Description

Technical Field

[0001] The utility model belongs to the technical field of lithium battery protection boards, and in particular relates to a capacitive load pre-charging control circuit and system. Background Art

[0002] Lithium battery protection board is an integrated circuit board that protects rechargeable batteries (generally lithium batteries). In the application process of lithium batteries, their loads usually have large input capacitance (hereinafter referred to as "load capacitance"), which is used to stabilize voltage and absorb instantaneous current fluctuations. If the discharge MOS tube (Metal Oxide semiconductor Field Effect transistor, a switching element) is directly turned on to charge the load capacitance, a very high current will appear instantly, that is, "surge current" will be generated. The surge current can be as high as 1000A or even several thousand amperes, and the high current has certain negative effects on the battery and the load, such as overheating of the battery, shortening of life, or damage to the electronic components of the load.

[0003] In order to deal with surge current, the common solution is to use a load pre-charging circuit. The main function of the pre-charging circuit is to charge the load capacitor with a lower current before the main circuit is connected to avoid excessive surge current when directly connected. In the prior art, it is usually achieved by connecting a current limiting resistor in series in the circuit to suppress the charging current. However, in the process of using the prior art, the inventor found that there are at least the following problems in the prior art:

[0004] When the pre-charging current demand of the load pre-charging circuit is large, a power resistor with a smaller resistance and larger volume is required, but the lithium battery protection board usually does not have such space to place such a high-power resistor. Utility Model Content

[0005] In order to solve the above technical problems at least to a certain extent, the utility model provides a capacitive load pre-charging control circuit and system.

[0006] In order to achieve the above purpose, the utility model adopts the following technical solutions:

[0007] A capacitive load pre-charging control circuit comprises a constant current circuit and a charge and discharge control circuit, wherein the constant current circuit comprises a DC conversion circuit, a switch circuit, a current sampling circuit, a first freewheeling diode and an energy storage inductor, and the charge and discharge control circuit comprises a charging control circuit and a discharging control circuit; the driving end of the DC conversion circuit is connected to the controlled end of the switch circuit, the current sampling end of the DC conversion circuit and the output end of the switch circuit are both connected to the negative electrode of a battery through the current sampling circuit, the input end of the switch circuit is connected to the positive electrode of the battery through the first freewheeling diode, the input end of the switch circuit is also respectively connected to the input end of the charging control circuit and the input end of the discharging control circuit through the energy storage inductor, the output end of the charging control circuit is used to connect to the positive electrode of the battery through a load device, the output end of the discharging control circuit is connected to the negative electrode of the battery, and the controlled end of the DC conversion circuit, the controlled end of the charging control circuit and the controlled end of the discharging control circuit are all connected to a main control circuit.

[0008] In a possible design, the constant current circuit also includes a pre-charge switch control circuit, and the controlled end of the DC conversion circuit is connected to the main control circuit through the pre-charge switch control circuit.

[0009] In one possible design, the pre-charge switch control circuit includes a photocoupler, a fourth resistor, a fifth resistor and a second capacitor. The positive electrode of the light-emitting diode in the photocoupler is connected to the main control circuit, the negative electrode of the light-emitting diode in the photocoupler is grounded through the fourth resistor, the collector of the switch tube in the photocoupler is connected to a 12V power supply, the emitter of the switch tube in the photocoupler is connected to the controlled end of the DC conversion circuit through the fifth resistor and the second capacitor in sequence, the junction point of the fifth resistor and the second capacitor is connected to the power input end of the DC conversion circuit, and the junction point of the second capacitor and the controlled end of the DC conversion circuit is grounded.

[0010] In a possible design, the switching circuit includes a first N-type MOS transistor and a seventh resistor, the gate of the first N-type MOS transistor serving as the controlled end of the switching circuit is connected to the driving end of the DC conversion circuit through the seventh resistor, the source of the first N-type MOS transistor serving as the output end of the switching circuit is connected to the negative electrode of the battery through the current sampling circuit, the drain of the first N-type MOS transistor serving as the input end of the switching circuit is connected to the positive electrode of the battery through the first freewheeling diode, and the drain of the first N-type MOS transistor serving as the input end of the switching circuit is also connected to the input end of the charging control circuit and the input end of the discharging control circuit respectively through the energy storage inductor.

[0011] In one possible design, the current sampling circuit includes a tenth resistor, a twelfth resistor and a sixth capacitor, one end of the tenth resistor is connected to the current sampling end of the DC conversion circuit, the other end of the tenth resistor is connected to the negative electrode of the battery through the twelfth resistor, the junction point of the tenth resistor and the twelfth resistor is connected to the output end of the switching circuit, one end of the sixth capacitor is connected to the current sampling end of the DC conversion circuit, and the other end of the sixth capacitor is connected to the negative electrode of the battery.

[0012] In one possible design, the capacitive load pre-charging control circuit also includes an RCD absorption circuit, which includes a second freewheeling diode, a first capacitor and a third resistor, the positive electrode of the second freewheeling diode is connected to one end of the energy storage inductor, the negative electrode of the second freewheeling diode is connected to the other end of the energy storage inductor through the first capacitor, and the third resistor is connected in parallel with the first capacitor.

[0013] In a possible design, the charging control circuit includes a first resistor, a second resistor and a second N-type MOS transistor, the gate of the second N-type MOS transistor serving as a controlled end of the charging control circuit is connected to the main control circuit through the second resistor, the drain of the second N-type MOS transistor serving as an input end of the charging control circuit is connected to the input end of the switching circuit, the source of the second N-type MOS transistor serving as an output end of the charging control circuit is connected to the load device, and the junction point of the second resistor and the main control circuit is connected to the source of the second N-type MOS transistor through the first resistor.

[0014] In a possible design, the discharge control circuit includes an eighth resistor, a ninth resistor and a third N-type MOS transistor, the gate of the third N-type MOS transistor serving as a controlled end of the discharge control circuit is connected to the main control circuit through the eighth resistor, the junction point between the eighth resistor and the main control circuit is connected to the source of the third N-type MOS transistor through the ninth resistor, the source of the third N-type MOS transistor serving as an output end of the discharge control circuit is connected to the negative electrode of the battery, and the drain of the third N-type MOS transistor serving as an input end of the discharge control circuit is connected to the input end of the switch circuit.

[0015] A capacitive load pre-charging control system comprises the capacitive load pre-charging control circuit as described in any one of the above items.

[0016] In one possible design, the capacitive load pre-charging control system also includes a main control circuit, which includes a main controller and a drive circuit. The main controller is connected to the controlled end of the DC conversion circuit, and the main controller is also connected to the controlled end of the charging control circuit and the controlled end of the discharging control circuit through the drive circuit.

[0017] The beneficial effects of the utility model are concentrated in that the current limiting function can be realized through the constant current circuit, and the surge current can be effectively controlled in a limited space, and thus can be widely used in lithium battery protection boards. Specifically, during the implementation of the utility model, first, the Pre-dischar signal of the controlled end of the DC conversion circuit is pulled high by the preset main control circuit, and the constant current circuit is started to pre-charge the load capacitor in the load device. In this process, the voltage of the load capacitor can be gradually increased to make it close to the battery voltage, thereby avoiding the surge current caused by sudden discharge; when the voltage of the load capacitor reaches the expected value, the Discharge-gate signal of the controlled end of the discharge control circuit is pulled high by the main control circuit, so that the switch circuit is turned on, and at this time, the battery starts to supply power to the load device; finally, the Pre-dischar signal of the controlled end of the DC conversion circuit is pulled low by the main control circuit, and the capacitive load pre-charging control circuit in this embodiment is turned off. In this process, the constant current circuit can ensure the stable output of the current and avoid the influence caused by the instantaneous large current. Therefore, the utility model can accurately control the current and realize the effective current limiting function even in a small space, thereby avoiding the problem of surge current while not taking up too much space, and is very suitable for use in lithium battery protection boards. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a circuit schematic diagram of a capacitive load pre-charging control circuit in an embodiment. DETAILED DESCRIPTION

[0019] In order to more clearly illustrate the technical solutions in the embodiments of the utility model or the prior art, the utility model will be briefly introduced below in combination with the drawings and the description of the embodiments or the prior art. Obviously, the following description of the structure of the drawings is only some embodiments of the utility model. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work. It should be noted that the description of these embodiments is used to help understand the utility model, but does not constitute a limitation of the utility model.

[0020] Embodiment 1:

[0021] like Figure 1As shown, this embodiment provides a capacitive load pre-charging control circuit, including a constant current circuit and a charge and discharge control circuit, the constant current circuit includes a DC conversion circuit, a switch circuit, a current sampling circuit, a first freewheeling diode D1 and an energy storage inductor L1, and the charge and discharge control circuit includes a charging control circuit and a discharging control circuit; the driving end of the DC conversion circuit is connected to the controlled end of the switch circuit, the current sampling end of the DC conversion circuit and the output end of the switch circuit are both connected to the negative electrode of the battery through the current sampling circuit, the input end of the switch circuit is connected to the positive electrode of the battery through the first freewheeling diode D1, and the switch circuit The input end of the battery is also connected to the input end of the charging control circuit and the input end of the discharging control circuit respectively through the energy storage inductor L1. Specifically, one end of the energy storage inductor L1 is connected to the input end of the switching circuit, and the other end of the energy storage inductor L1 is connected to the input end of the charging control circuit and the input end of the discharging control circuit respectively; the output end of the charging control circuit is used to connect to the positive electrode of the battery through a load device, and the output end of the discharging control circuit is connected to the negative electrode of the battery. The controlled end of the DC conversion circuit, the controlled end of the charging control circuit and the controlled end of the discharging control circuit are all connected to the main control circuit.

[0022] It should be noted that, during the implementation of this embodiment, one end of the load device is connected to the output end of the charging control circuit, and the other end of the load device is connected to the positive electrode of the battery. When the switch circuit is closed, the current flow path and direction are: the positive electrode of the battery → the load device → the charging control circuit → the energy storage inductor L1 → the switch circuit → the current sampling circuit → the discharge control circuit → the negative electrode of the battery, so that the battery can provide power support to the load device, and at the same time, it is convenient for the capacitive load pre-charging control circuit in this embodiment to limit the discharge current of the load device, realize the pre-charging of the load capacitor in the load device, and reduce the surge current at the moment of the switch circuit opening. When the switch circuit is disconnected, the current flow path and direction are: one end of the energy storage inductor L1 → the first freewheeling diode D1 → the B+ end derived from the cathode of the first freewheeling diode D1 flows through the load device → the charging control circuit → the other end of the energy storage inductor L1. The first freewheeling diode D1 can allow the current of the energy storage inductor L1 to continue during the switching process of the switching circuit, preventing the current from suddenly changing, so as to ensure the smooth conversion and stability of the circuit.

[0023] This embodiment can realize the current limiting function through the constant current circuit, can effectively control the surge current in a limited space, and can be widely used in lithium battery protection boards.

[0024] Specifically, in the implementation process of this embodiment, first, the Pre-dischar signal (switch control signal of the pre-charging function) of the controlled end of the DC conversion circuit is pulled high by the preset main control circuit, and the constant current circuit is started to pre-charge the load capacitor in the load device. In this process, the voltage of the load capacitor can be gradually increased to be close to the battery voltage, thereby avoiding the surge current caused by sudden discharge. This process usually takes 3 to 5 seconds; when the voltage of the load capacitor reaches the expected value, the Discharge-gate signal (discharge switch control signal) of the controlled end of the discharge control circuit is pulled high by the main control circuit, so that the switch circuit is turned on. At this time, the battery starts to supply power to the load device; finally, the Pre-dischar signal of the controlled end of the DC conversion circuit is pulled low by the main control circuit, and the capacitive load pre-charging control circuit in this embodiment is turned off. In this process, the constant current circuit can ensure the stable output of the current and avoid the influence caused by the instantaneous large current. Therefore, this embodiment can accurately control the current and achieve an effective current limiting function even in a small space, thereby avoiding the problem of surge current while not taking up too much space, and is very suitable for use in a lithium battery protection board.

[0025] In this embodiment, the constant current circuit further includes a pre-charge switch control circuit, and the controlled end of the DC conversion circuit is connected to the main control circuit via the pre-charge switch control circuit. It should be noted that the setting of the pre-charge switch control circuit can electrically isolate the main control circuit from the DC conversion circuit, thereby preventing the DC conversion circuit from causing adverse effects on the main control circuit.

[0026] In this embodiment, the pre-charge switch control circuit includes a photoelectric coupler U2, a fourth resistor R4, a fifth resistor R5 and a second capacitor C2. The positive electrode of the light-emitting diode in the photoelectric coupler U2 is connected to the main control circuit, and the negative electrode of the light-emitting diode in the photoelectric coupler U2 is grounded through the fourth resistor R4. The collector of the switch tube in the photoelectric coupler U2 is connected to a 12V power supply, and the emitter of the switch tube in the photoelectric coupler U2 is connected to the controlled end of the DC conversion circuit through the fifth resistor R5 and the second capacitor C2 in sequence. The junction point of the fifth resistor R5 and the second capacitor C2 is connected to the power input end of the DC conversion circuit, and the junction point of the second capacitor C2 and the controlled end of the DC conversion circuit is grounded.

[0027] Specifically, in this embodiment, the DC conversion circuit includes a CN5120 type PWM (Pulse width modulation wave) controller U1, the 8th pin of the PWM controller U1 is connected to the controlled end of the switch circuit as the driving end of the DC conversion circuit, the 10th pin of the PWM controller U1 is connected to the current sampling circuit as the current sampling end of the DC conversion circuit, the 5th pin of the PWM controller U1 is connected to the pre-charge switch control circuit as the controlled end of the DC conversion circuit, and the 6th pin of the PWM controller U1 is connected to the combination point of the fifth resistor R5 and the second capacitor C2 as the power input end of the DC conversion circuit. In addition, in this embodiment, the 9th pin of the PWM controller U1 is grounded, the 2nd pin of the PWM controller U1 is grounded through the 11th resistor R11, the 7th pin of the PWM controller U1 is grounded through the third capacitor, the 3rd pin of the PWM controller U1 is grounded once through the sixth resistor R6 and the fourth capacitor C4, and the 3rd pin of the PWM controller U1 is also grounded through the fifth capacitor C5.

[0028] In this embodiment, the switch circuit includes a first N-type MOS transistor Q1 and a seventh resistor R7, the gate of the first N-type MOS transistor Q1 is connected to the driving end of the DC conversion circuit through the seventh resistor R7 as the controlled end of the switch circuit, the source of the first N-type MOS transistor Q1 is connected to the negative electrode of the battery through the current sampling circuit as the output end of the switch circuit, the drain of the first N-type MOS transistor Q1 is connected to the positive electrode of the battery through the first freewheeling diode D1 as the input end of the switch circuit, and the drain of the first N-type MOS transistor Q1 is connected to the input end of the charging control circuit and the input end of the discharging control circuit through the energy storage inductor L1 as the input end of the switch circuit. It should be noted that the seventh resistor R7 plays the role of limiting the driving current, controlling the switching speed, and protecting the first N-type MOS transistor Q1.

[0029] In this embodiment, the current sampling circuit includes a tenth resistor R10, a twelfth resistor R12 and a sixth capacitor C6, one end of the tenth resistor R10 is connected to the current sampling end of the DC conversion circuit, the other end of the tenth resistor R10 is connected to the negative electrode of the battery through the twelfth resistor R12, the junction point of the tenth resistor R10 and the twelfth resistor R12 is connected to the output end of the switch circuit, one end of the sixth capacitor C6 is connected to the current sampling end of the DC conversion circuit, and the other end of the sixth capacitor C6 is connected to the negative electrode of the battery. It should be noted that in this embodiment, the twelfth resistor R12 is a current sampling resistor, and the tenth resistor R10 and the sixth capacitor C6 are combined to form an RC filter circuit in the current sampling circuit, which is used to filter out high-frequency noise in the current detection signal and smooth the current signal to ensure that the DC conversion circuit receives a stable current signal.

[0030] In this embodiment, the capacitive load pre-charging control circuit also includes an RCD absorption circuit (a circuit composed of a resistor, a capacitor and a diode), and the RCD absorption circuit includes a second freewheeling diode D2, a first capacitor C1 and a third resistor R3, the positive electrode of the second freewheeling diode D2 is connected to one end of the energy storage inductor L1, the negative electrode of the second freewheeling diode D2 is connected to the other end of the energy storage inductor L1 through the first capacitor C1, and the third resistor R3 is connected in parallel with the first capacitor C1. It should be noted that in this embodiment, the RCD absorption circuit plays a role in suppressing power supply fluctuations and electromagnetic interference in the power supply circuit. Specifically, the RCD absorption circuit is a filter composed of an inductor element, a capacitor element and a resistive element, which can absorb and reduce the high-frequency electromagnetic waves and interference signals in the power supply, make the power supply output more stable, reduce equipment failures or abnormal operations caused by electromagnetic waves and interference, etc., and help improve the reliability and stability of the capacitive load pre-charging control circuit in this embodiment, while protecting it from electromagnetic interference.

[0031] In this embodiment, the charging control circuit includes a first resistor R1, a second resistor R2 and a second N-type MOS transistor Q2, the gate of the second N-type MOS transistor Q2 is connected to the main control circuit through the second resistor R2 as the controlled end of the charging control circuit, the drain of the second N-type MOS transistor Q2 is connected to the input end of the switch circuit as the input end of the charging control circuit, the source of the second N-type MOS transistor Q2 is connected to the load device as the output end of the charging control circuit, and the junction point of the second resistor R2 and the main control circuit is connected to the source of the second N-type MOS transistor Q2 through the first resistor R1. It should be noted that the charging control circuit plays a role in controlling the charging of the battery.

[0032] In this embodiment, the discharge control circuit includes an eighth resistor R8, a ninth resistor R9 and a third N-type MOS transistor Q3, the gate of the third N-type MOS transistor Q3 is connected to the main control circuit through the eighth resistor R8 as the controlled end of the discharge control circuit, the junction point of the eighth resistor R8 and the main control circuit is connected to the source of the third N-type MOS transistor Q3 through the ninth resistor R9, the source of the third N-type MOS transistor Q3 is connected to the negative electrode of the battery as the output end of the discharge control circuit, and the drain of the third N-type MOS transistor Q3 is connected to the input end of the switch circuit as the input end of the discharge control circuit. It should be noted that the discharge control circuit plays a role in controlling the discharge of the battery.

[0033] In this embodiment, in order to achieve current limiting protection for the battery, the current sampling circuit and the discharge control circuit are both connected to the negative electrode of the battery through the thirteenth resistor R13, and correspondingly, the junction point of the ninth resistor R9 and the source of the third N-type MOS tube Q3, and the junction point of the sixth capacitor C6 and the twelfth resistor R12 are all grounded.

[0034] The working principle of the capacitive load pre-charging control circuit is described in detail below in combination with the components in the capacitive load pre-charging control circuit: the PWM controller U1 in the DC conversion circuit adjusts the PWM duty cycle according to the current current value fed back by the twelfth resistor R12 in the current sampling circuit. The PWM controller U1 drives the first N-type MOS tube Q1 through the 8-pin output. When the first N-type MOS tube Q1 is turned on, the current of the energy storage inductor L1 increases as the turn-on time increases; when the current current value is higher than the target current value, the PWM controller U1 will reduce the PWM duty cycle to reduce the current flowing to the load device. When the current current value is lower than the target current value, the PWM controller U1 will increase the PWM duty cycle to increase the current flowing to the load device so that the actual current value reaches the target current value, thereby achieving the function of dynamically adjusting the current.

[0035] Embodiment 2:

[0036] This embodiment discloses a capacitive load pre-charging control system, including a capacitive load pre-charging control circuit as described in any one of Embodiment 1.

[0037] Specifically, in this embodiment, the capacitive load pre-charging control system also includes a main control circuit, which includes a main controller and a drive circuit. The main controller is connected to the controlled end of the DC conversion circuit, and the main controller is also connected to the controlled end of the charging control circuit and the controlled end of the discharge control circuit through the drive circuit.

[0038] Finally, it should be noted that the above is only a preferred embodiment of the utility model and is not intended to limit the protection scope of the utility model. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the utility model shall be included in the protection scope of the utility model.

Claims

1. A capacitive load pre-charging control circuit, characterized in that: The invention comprises a constant current circuit and a charge and discharge control circuit, wherein the constant current circuit comprises a DC conversion circuit, a switch circuit, a current sampling circuit, a first freewheeling diode (D1) and an energy storage inductor (L1), and the charge and discharge control circuit comprises a charging control circuit and a discharging control circuit; the driving end of the DC conversion circuit is connected to the controlled end of the switch circuit, the current sampling end of the DC conversion circuit and the output end of the switch circuit are both connected to the negative electrode of a battery through the current sampling circuit, the input end of the switch circuit is connected to the positive electrode of the battery through the first freewheeling diode (D1), the input end of the switch circuit is also respectively connected to the input end of the charging control circuit and the input end of the discharging control circuit through the energy storage inductor (L1), the output end of the charging control circuit is used to connect to the positive electrode of the battery through a load device, the output end of the discharging control circuit is connected to the negative electrode of the battery, and the controlled end of the DC conversion circuit, the controlled end of the charging control circuit and the controlled end of the discharging control circuit are all connected to a main control circuit.

2. A capacitive load precharge control circuit according to claim 1, characterized in that: The constant current circuit also includes a pre-charge switch control circuit, and the controlled end of the DC conversion circuit is connected to the main control circuit through the pre-charge switch control circuit.

3. A capacitive load precharge control circuit according to claim 2, characterized in that: The pre-charge switch control circuit comprises a photoelectric coupler (U2), a fourth resistor (R4), a fifth resistor (R5) and a second capacitor (C2); the positive electrode of the light-emitting diode in the photoelectric coupler (U2) is connected to the main control circuit; the negative electrode of the light-emitting diode in the photoelectric coupler (U2) is grounded through the fourth resistor (R4); the collector of the switch tube in the photoelectric coupler (U2) is connected to a 12V power supply; the emitter of the switch tube in the photoelectric coupler (U2) is connected to the controlled end of the DC conversion circuit through the fifth resistor (R5) and the second capacitor (C2) in sequence; the junction point of the fifth resistor (R5) and the second capacitor (C2) is connected to the power input end of the DC conversion circuit; and the junction point of the second capacitor (C2) and the controlled end of the DC conversion circuit is grounded.

4. A capacitive load precharge control circuit according to claim 1, characterized in that: The switch circuit comprises a first N-type MOS transistor (Q1) and a seventh resistor (R7); the gate of the first N-type MOS transistor (Q1) is connected to the driving end of the DC conversion circuit via the seventh resistor (R7) as the controlled end of the switch circuit; the source of the first N-type MOS transistor (Q1) is connected to the negative electrode of the battery via the current sampling circuit as the output end of the switch circuit; the drain of the first N-type MOS transistor (Q1) is connected to the positive electrode of the battery via the first freewheeling diode (D1) as the input end of the switch circuit; and the drain of the first N-type MOS transistor (Q1) is connected to the input end of the charging control circuit and the input end of the discharging control circuit via the energy storage inductor (L1) as the input end of the switch circuit.

5. A capacitive load precharge control circuit according to claim 1, characterized in that: The current sampling circuit comprises a tenth resistor (R10), a twelfth resistor (R12) and a sixth capacitor (C6), one end of the tenth resistor (R10) is connected to the current sampling end of the DC conversion circuit, the other end of the tenth resistor (R10) is connected to the negative electrode of the battery through the twelfth resistor (R12), a junction point between the tenth resistor (R10) and the twelfth resistor (R12) is connected to the output end of the switch circuit, one end of the sixth capacitor (C6) is connected to the current sampling end of the DC conversion circuit, and the other end of the sixth capacitor (C6) is connected to the negative electrode of the battery.

6. A capacitive load precharge control circuit according to claim 1, characterized in that: The capacitive load pre-charging control circuit also includes an RCD absorption circuit, which includes a second freewheeling diode (D2), a first capacitor (C1) and a third resistor (R3), wherein the positive electrode of the second freewheeling diode (D2) is connected to one end of the energy storage inductor (L1), the negative electrode of the second freewheeling diode (D2) is connected to the other end of the energy storage inductor (L1) through the first capacitor (C1), and the third resistor (R3) is connected in parallel with the first capacitor (C1).

7. A capacitive load precharge control circuit according to claim 1, characterized in that: The charging control circuit comprises a first resistor (R1), a second resistor (R2) and a second N-type MOS transistor (Q2); the gate of the second N-type MOS transistor (Q2) is connected to the main control circuit via the second resistor (R2) as a controlled end of the charging control circuit; the drain of the second N-type MOS transistor (Q2) is connected to the input end of the switch circuit as an input end of the charging control circuit; the source of the second N-type MOS transistor (Q2) is connected to the load device as an output end of the charging control circuit; and the junction point between the second resistor (R2) and the main control circuit is connected to the source of the second N-type MOS transistor (Q2) via the first resistor (R1).

8. A capacitive load precharge control circuit according to claim 1, characterized in that: The discharge control circuit comprises an eighth resistor (R8), a ninth resistor (R9) and a third N-type MOS transistor (Q3); the gate of the third N-type MOS transistor (Q3) is connected to the main control circuit through the eighth resistor (R8) as a controlled end of the discharge control circuit; the junction point between the eighth resistor (R8) and the main control circuit is connected to the source of the third N-type MOS transistor (Q3) through the ninth resistor (R9); the source of the third N-type MOS transistor (Q3) is connected to the negative electrode of the battery as an output end of the discharge control circuit; and the drain of the third N-type MOS transistor (Q3) is connected to the input end of the switch circuit as an input end of the discharge control circuit.

9. A capacitive load pre-charging control system, characterized in that: Comprising a capacitive load pre-charging control circuit as described in any one of claims 1 to 8.

10. A capacitive load pre-charging control system according to claim 9, characterized in that: The capacitive load pre-charging control system also includes a main control circuit, which includes a main controller and a drive circuit. The main controller is connected to the controlled end of the DC conversion circuit, and the main controller is also connected to the controlled end of the charging control circuit and the controlled end of the discharging control circuit respectively through the drive circuit.

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