Vehicle-mounted power supply circuit

Abstract

A vehicle-mounted power supply circuit disclosed by the present invention comprises a voltage-limiting anti-overvoltage circuit and a voltage reduction circuit, the voltage-limiting anti-overvoltage circuit comprises a switching tube and a voltage-limiting anti-overvoltage control circuit, the D pole of the switching tube is connected with an input power supply and the positive pole of a diode D3, and the negative pole of the diode D3 is connected with the G pole of the switching tube. The S pole of the switch tube is connected with the input end of the step-down circuit, the voltage limiting and overvoltage preventing control circuit comprises a booster circuit and a voltage stabilizing circuit, the booster circuit is used for boosting the G pole voltage of the switch tube to be higher than the S pole voltage of the switch tube, and the voltage stabilizing circuit is used for stabilizing the G pole voltage of the switch tube at a set value. And the switching tube is switched on when the input power supply voltage is within the set voltage range. According to the vehicle-mounted power supply circuit, the voltage limiting and overvoltage preventing circuit is arranged in front of the step-down circuit and used for protecting the post-stage step-down circuit, lowering the requirement for the input voltage of the post-stage step-down circuit, lowering the model selection requirement for a post-stage power supply chip and a filter capacitor and lowering the cost.

Description

Technical Field

[0001] The invention relates to a power supply circuit, in particular to a vehicle-mounted power supply circuit. Background Art

[0002] At present, the on-board power supply circuit of on-board electronic products adopts a step-down circuit, which steps down the car power voltage to the voltage required by the relevant functional modules of the on-board products through the step-down circuit. Because of the power switch on and off and the high-power inductive load environment on the vehicle, some voltage pulses higher than the input power will be generated on the power supply. For example, in the simulation of the vehicle power supply environment experiment, for the 24V system, the 5b experiment of ISO7637 is performed, and it is assumed that the step-down circuit must pass a 48V power pulse with a time of 100ms-350ms. In order to adapt to the fluctuation of the on-board power supply voltage, the step-down circuit must use a high-voltage, wide-input power chip and capacitor. For example, the default power chip withstand voltage needs to reach 60V, and the capacitor withstand voltage reaches 50V or 100V. This makes the selection of power chip difficult, the cost is high, and the risk of power failure rate is high. Summary of the invention

[0003] The present invention aims to solve at least one of the technical problems existing in the prior art, and proposes a vehicle-mounted power supply circuit. The vehicle-mounted power supply circuit of the present invention is provided with a voltage limiting and overvoltage protection circuit before the step-down circuit, which is used to protect the subsequent step-down circuit, reduce the input voltage requirement of the subsequent step-down circuit, reduce the selection requirements of the subsequent power chip and filter capacitor, and reduce the cost.

[0004] The technical solution of the present invention is implemented as follows: The present invention discloses a vehicle-mounted power supply circuit, including a voltage-limiting overvoltage protection circuit and a voltage-step-down circuit, the voltage-limiting overvoltage protection circuit including a switch tube and a voltage-limiting overvoltage protection control circuit, the first pole of the switch tube is connected to the input power supply and the positive pole of the diode D3, the negative pole of the diode D3 is connected to the control pole of the switch tube, the second pole of the switch tube is connected to the input end of the voltage-step-down circuit, the voltage-limiting overvoltage protection control circuit includes a boost circuit and a voltage stabilizing circuit, the boost circuit is used to increase the control pole voltage of the switch tube to a voltage higher than the second pole voltage of the switch tube, and the voltage stabilizing circuit is used to stabilize the control pole voltage of the switch tube at a set value, so that the switch tube is turned on when the input power supply voltage is within the set voltage range.

[0005] Furthermore, a resistor R1 is connected in series between the anode of the diode D3 and the first electrode of the switch tube.

[0006] Furthermore, the boost circuit includes a capacitor C1, a capacitor C12, a diode D1 and a diode D2, one end of the capacitor C1 is connected to the output end SW of the power chip of the buck circuit, the other end of the capacitor C1 is respectively connected to the positive electrode of the diode D1 and the negative electrode of the diode D2, the positive electrode of the diode D2 is connected to the second electrode of the switch tube, the negative electrode of the diode D1 is connected to the control electrode of the switch tube and one end of the capacitor C12, and the other end of the capacitor C12 is grounded.

[0007] Furthermore, a resistor R4 is connected in series between the cathode of the diode D1 and the control electrode of the switch tube.

[0008] Furthermore, the voltage stabilizing circuit includes a voltage stabilizing tube D5, a cathode of the voltage stabilizing tube D5 is connected to a control electrode of the switch tube, and a cathode of the voltage stabilizing tube D5 is grounded.

[0009] Furthermore, the step-down circuit is used to step down the input power supply voltage to the required voltage output; the step-down circuit includes a Buck power supply chip, the input end of the Buck power supply chip is respectively connected to the second pole of the switch tube and one end of the resistor R2, the other end of the resistor R2 is respectively connected to one end of the resistor R5 and the EN pin of the Buck power supply chip, the other end of the resistor R5 is grounded, the SW pin of the Buck power supply chip is respectively connected to one end of the resistor R3, the input end of the voltage limiting and overvoltage protection control circuit, one end of the inductor L2 and the negative electrode of the diode D4, the other end of the resistor R3 is connected to one end of the capacitor C2, the other end of the capacitor C2 is connected to the BOOT pin of the Buck power supply chip, the positive electrode of the diode D4 is grounded, the other end of the inductor L2 is respectively connected to one end of the resistor R6 and the output end of the step-down circuit, the other end of the resistor R6 is respectively connected to the FB pin of the Buck power supply chip and one end of the resistor R9, and the other end of the resistor R9 is grounded.

[0010] Furthermore, a capacitor C11 is connected in parallel between both ends of the resistor R6;

[0011] and / or,

[0012] The step-down circuit further includes a capacitor C7, a capacitor C8, and a capacitor C9, one end of the capacitor C7, one end of the capacitor C8, and one end of the capacitor C9 are connected to the input end of the Buck power chip, and the other end of the capacitor C7, the other end of the capacitor C8, and the other end of the capacitor C9 are grounded;

[0013] and / or,

[0014] The step-down circuit further includes a capacitor C13, a capacitor C14, and a capacitor C15, one end of the capacitor C13, one end of the capacitor C14, and one end of the capacitor C15 are connected to the output end of the step-down circuit, and the other end of the capacitor C13, the other end of the capacitor C14, and the other end of the capacitor C15 are grounded;

[0015] and / or,

[0016] The step-down circuit further includes a capacitor CE1 , one end of the capacitor CE1 is connected to the output end of the step-down circuit, and the other end of the capacitor CE1 is grounded.

[0017] Furthermore, the vehicle-mounted power supply circuit of the present invention further includes an input filter circuit, the input end of the input filter circuit is connected to the vehicle-mounted power supply, and the output end of the input filter circuit is connected to the first pole of the switch tube.

[0018] Furthermore, the input filter circuit includes capacitor C3, capacitor C10, inductor L1, capacitor C4, capacitor C6, and capacitor C5. One end of capacitor C3 is connected to one end of inductor L1 and the vehicle power supply, the other end of capacitor C3 is connected to one end of capacitor C10, the other end of capacitor C10 is grounded, the other end of inductor L1 is respectively connected to one end of capacitor C4, one end of capacitor C6, and one end of capacitor C5, and the other end of capacitor C4, the other end of capacitor C6, and the other end of capacitor C5 are grounded.

[0019] Furthermore, the switch tube is an N-type transistor, the first pole of the switch tube is a D pole, the second pole of the switch tube is an S pole, and the control pole of the switch tube is a G pole.

[0020] Compared with the prior art, the present invention has the following beneficial effects: the vehicle-mounted power supply circuit of the present invention is provided with a voltage-limiting overvoltage protection circuit before the step-down circuit, the voltage-limiting overvoltage protection circuit includes a switch tube and a voltage-limiting overvoltage protection control circuit, the first pole of the switch tube is connected to the input power supply, the first pole of the switch tube is connected to the positive pole of the diode D3, the negative pole of the diode D3 is connected to the control pole of the switch tube, the second pole of the switch tube is connected to the input end of the step-down circuit, the control pole of the switch tube is connected to the voltage-limiting overvoltage protection control circuit, and the voltage-limiting overvoltage protection control circuit is used to respond to the SW switch signal of the step-down circuit (i.e., the SW signal of the subsequent BUCK DCDC chip) to control the control pole voltage of the switch tube.

[0021] The voltage limiting overvoltage protection circuit of the present invention is used to protect the subsequent step-down circuit. Through the protection of the voltage limiting overvoltage protection circuit, the related chips of the subsequent step-down circuit do not need to select power chips with very high voltage and wide input voltage range, which reduces the input voltage requirements of the subsequent step-down circuit, reduces the selection requirements of the power chips and filter capacitors of the subsequent step-down circuit, and reduces the cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 A principle block diagram of a vehicle-mounted power supply circuit provided by an embodiment of the present invention;

[0023] Figure 2 A circuit diagram of an input filter circuit provided by an embodiment of the present invention;

[0024] Figure 3 A circuit diagram of a voltage limiting and overvoltage protection circuit provided by an embodiment of the present invention;

[0025] Figure 4 A circuit diagram of a step-down circuit provided in accordance with an embodiment of the present invention. DETAILED DESCRIPTION

[0026] In order to enable those skilled in the art to better understand the technical solution of the present invention, the technical solution in the embodiment of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiment of the present invention. Obviously, the described embodiment is a part of the embodiment of the present invention, not all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0027] See also Figures 1 to 4 The embodiment of the present invention discloses a vehicle-mounted power supply circuit, including a voltage-limiting overvoltage protection circuit and a voltage-reducing circuit. The voltage-limiting overvoltage protection circuit includes a switch tube and a voltage-limiting overvoltage protection control circuit. The first electrode of the switch tube is connected to the input power supply and the positive electrode of the diode D3, the negative electrode of the diode D3 is connected to the control electrode of the switch tube, and the second electrode of the switch tube is connected to the input end of the voltage-reducing circuit. The voltage-limiting overvoltage protection control circuit includes a boost circuit and a voltage stabilizing circuit. The boost circuit is used to increase the control electrode voltage of the switch tube to a voltage higher than the second electrode voltage of the switch tube after the switch tube is turned on. The voltage stabilizing circuit is used to stabilize the control electrode voltage of the switch tube at a set value, so that the switch tube is turned on when the input power supply voltage is within the set voltage range, and the switch tube is turned off when the input power supply voltage exceeds the set voltage range. The set voltage range is set according to actual needs, such as adjusting the voltage stabilizing tube according to different application scenarios. For example, when the input power supply voltage is lower than the set value, the switch tube is turned on; when the input power supply voltage is higher than the set value, the switch tube is turned off.

[0028] Furthermore, a resistor R1 is connected in series between the anode of the diode D3 and the first electrode of the switch tube.

[0029] After the switch tube Q1 is turned on, the buck circuit is used to step down the input power supply voltage to the required voltage output. For example, the CAR_POWER power supply is stepped down to the voltage required by the relevant functional modules of the vehicle-mounted product through the BUCK_DCDC of the subsequent buck circuit for power supply. The diode D3 is used to isolate the G pole voltage of the switch tube Q1 from the input voltage. If there is no diode D3, the boost voltage of the G pole of the switch tube Q1 will affect the input voltage through R1.

[0030] The switch tube of the present invention is an N-type transistor, the first pole of the switch tube is a D pole, the second pole of the switch tube is an S pole, and the control pole of the switch tube is a G pole. Preferably, the switch tube is an NMOS transistor.

[0031] Because the vehicle-mounted power supply circuit of the present invention is provided with a voltage-limiting overvoltage protection circuit at the input end of the step-down circuit, when the input power exceeds the set value, the switch tube is turned off, that is, the input voltage of the step-down circuit is limited, and the withstand voltage of the chip and capacitor of the subsequent step-down circuit can be reduced, and a withstand voltage of 45V can be selected. The power chip and filter capacitor of the subsequent step-down circuit of the present invention can select chips and capacitors according to the lower voltage limited by the design, that is, the selection requirements of the subsequent power chip and filter capacitor are lowered. And the voltage-limiting overvoltage protection circuit adopts NMOS, which reduces the cost compared with PMOS with the same current. The voltage-limiting overvoltage protection circuit of the present invention can protect the subsequent step-down circuit, add a level of protection to the power circuit, and make the vehicle-mounted power supply circuit of the present invention safer and more reliable.

[0032] Furthermore, the boost circuit includes capacitor C1, capacitor C12, diode D1 and diode D2, one end of the capacitor C1 is connected to the output end SW of the power chip of the step-down circuit, the other end of the capacitor C1 is respectively connected to the positive electrode of the diode D1 and the negative electrode of the diode D2, the positive electrode of the diode D2 is connected to the second electrode of the switch tube, the negative electrode of the diode D1 is connected to the control electrode of the switch tube and one end of the capacitor C12, and the other end of the capacitor C12 is grounded. The voltage stabilizing circuit includes a voltage stabilizing tube D5, the negative electrode of the voltage stabilizing tube D5 is connected to the control electrode of the switch tube, and the positive electrode of the voltage stabilizing tube D5 is grounded.

[0033] The boost circuit of the present invention utilizes the SW switch signal of the buck circuit to raise the control electrode voltage of the switch tube to a voltage higher than the second electrode voltage of the switch tube, so as to drive the switch tube to conduct. When the input power supply voltage is higher than the set value, the switch tube is disconnected.

[0034] The voltage stabilizing circuit is selected according to the needs. The present invention uses a voltage stabilizing tube D5 to stabilize the control electrode of the switch tube. The present invention selects the corresponding voltage stabilizing tube according to the set value. For example, when the set value of an embodiment is 36V, the voltage stabilizing tube D5 uses a 36V voltage stabilizing tube.

[0035] Furthermore, a resistor R4 is connected in series between the cathode of the diode D1 and the control electrode of the switch tube.

[0036] Further, the step-down circuit includes a Buck power chip, the input end of the Buck power chip is respectively connected to the second pole of the switch tube and one end of the resistor R2, the other end of the resistor R2 is respectively connected to one end of the resistor R5 and the EN pin of the Buck power chip, the other end of the resistor R5 is grounded, the SW pin of the Buck power chip is respectively connected to one end of the resistor R3, the input end of the voltage limiting and overvoltage protection control circuit, one end of the inductor L2 and the negative electrode of the diode D4, the other end of the resistor R3 is connected to one end of the capacitor C2, the other end of the capacitor C2 is connected to the BOOT pin of the Buck power chip, the positive electrode of the diode D4 is grounded, the other end of the inductor L2 is respectively connected to one end of the resistor R6 and the output end of the step-down circuit, the other end of the resistor R6 is respectively connected to the FB pin of the Buck power chip and one end of the resistor R9, and the other end of the resistor R9 is grounded.

[0037] Furthermore, a capacitor C11 is connected in parallel between both ends of the resistor R6.

[0038] The step-down circuit also includes capacitors C7, C8 and C9. One end of capacitor C7, one end of capacitor C8 and one end of capacitor C9 are connected to the input end of the Buck power chip, and the other ends of capacitor C7, C8 and C9 are grounded.

[0039] The step-down circuit further includes capacitor C13, capacitor C14 and capacitor C15. One end of capacitor C13, one end of capacitor C14 and one end of capacitor C15 are connected to the output end of the step-down circuit, and the other end of capacitor C13, another end of capacitor C14 and another end of capacitor C15 are grounded.

[0040] The step-down circuit further includes a capacitor CE1 , one end of the capacitor CE1 is connected to the output end of the step-down circuit, and the other end of the capacitor CE1 is grounded.

[0041] Furthermore, the vehicle-mounted power supply circuit of the present invention further includes an input filter circuit, the input end of the input filter circuit is connected to the vehicle-mounted power supply, and the output end of the input filter circuit is connected to the first pole of the switch tube.

[0042] Furthermore, the input filter circuit includes capacitor C3, capacitor C10, inductor L1, capacitor C4, capacitor C6, and capacitor C5. One end of capacitor C3 is connected to one end of inductor L1 and the vehicle power supply, the other end of capacitor C3 is connected to one end of capacitor C10, the other end of capacitor C10 is grounded, the other end of inductor L1 is respectively connected to one end of capacitor C4, one end of capacitor C6, and one end of capacitor C5, and the other end of capacitor C4, the other end of capacitor C6, and the other end of capacitor C5 are grounded.

[0043] See also Figures 2 to 4, taking the commercial vehicle on-board power supply circuit as an example, the input power of the circuit is the commercial vehicle 24V power supply system. The present invention supplies power to the product through the power supply connector, and the car power CAR_POWER is connected through Figure 2 The filter circuit shown in the figure (including capacitors C3, C10, inductor L1 and capacitors C4, C6, C5) performs filtering and sends it to Figure 3 The D pole of the NMOS transistor Q1 of the voltage limiting and overvoltage protection circuit shown is simultaneously sent to the G pole of the NMOS transistor Q1 through the resistor R1 and the diode D3. At this time, the S pole voltage of the NMOS transistor Q1 is lower than the G pole, and the D pole and S pole of the NMOS transistor Q1 are turned on.

[0044] When the BUCK_DCDC chip of the subsequent step-down circuit is working, the SW switch signal of the 8-pin of the BUCK_DCDC chip and the capacitor C1, the diode D1, the diode D2, the resistor R4 and the capacitor C12 form a boost circuit, which raises the G pole voltage of the NMOS transistor Q1 to a voltage higher than the S pole of Q1 to ensure the conduction of the driver Q1.

[0045] During the voltage boosting process, after Q1 is powered on, CAR_VCC (24V) first charges C1 through D2, and C1 is quickly charged to 24V on the left side of the capacitor and 0V on the right side of the capacitor; at the same time, CAR_VCC (24V) first charges C12 through D2, D1, and R4, and C12 is quickly charged to 24V on the upper side of the capacitor and 0V on the lower side of the capacitor; after the BUCK_DCDC chip of the buck circuit works, because the MOS switch inside the BUCK_DCDC of the buck circuit switches, a pulse of switching between 0V and 24V voltage appears on the SW pin. When it switches to a pulse of 24V, because the voltage across the capacitor cannot suddenly change, the voltage of C1 becomes 48V on the left side of the capacitor and 24V on the right side of the capacitor; the 48V on the left side of C1 continues to charge C12 through D1 and R4, and due to the voltage stabilizing effect of the voltage regulator D5 (such as the 36V voltage regulator in this embodiment), the G pole voltage of Q1 is stabilized at 36V, which is higher than the S pole voltage of Q1, thereby ensuring the conduction of Q1. When switching to a 0V pulse, because the voltage across the capacitor cannot change suddenly, the voltage of C1 becomes 24V on the left side of the capacitor and 0V on the right side of the capacitor; but due to the isolation of D1 and D3, the G pole voltage of Q1 is stabilized at 36V, and Q1 is turned on.

[0046] Due to the voltage stabilizing effect of the voltage regulator D5 (such as the 36V voltage regulator in this embodiment), the G pole voltage of Q1 is stabilized at 36V. When CAR_POWER and CAR_VCC are higher than 36V, the S pole voltage of Q1 will be higher than the G pole, and Q1 will be disconnected, disconnecting the power supply of the subsequent stage to achieve the voltage limiting and overvoltage protection effect, thereby protecting the subsequent stage circuit.

[0047] After the NMOS transistor Q1 is turned on, the car power CAR_VCC (24V) is stepped down by the subsequent step-down circuit to the voltage VCC required by the relevant functional modules on the product, thereby supplying power to the relevant functional modules.

[0048] The circuit of the voltage limiting overvoltage protection circuit of the present invention is simple, and the voltage limiting overvoltage protection circuit is composed of the SW signal of the subsequent BUCK DCDC chip, NMOS and a few separate components, so as to control the NMOS so that the NMOS is turned on at an ideal and safe voltage of the vehicle-mounted product, thereby providing an ideal and safe power supply to the subsequent stage.

[0049] The present invention has many application scenarios and can be applied to power supply circuits with a large input power supply voltage variation range and a large step-down range. The present invention is also flexible in application. The current size can be adapted by selecting a switch tube Q1 (NMOS) with a suitable ID / RDS; the voltage adaptation, for example, the adaptation of different voltage systems such as passenger cars / commercial vehicles, can be met by selecting a voltage regulator tube D5 with a suitable voltage stabilization value, for example Figures 2 to 4 For commercial vehicle system applications, a 36V voltage regulator tube is selected.

[0050] The present invention can be used in commercial vehicles, passenger vehicles and vehicle-mounted electronic products covering new energy vehicles, and is specifically applied to the step-down power supply circuit of vehicle-mounted products.

[0051] It is to be understood that the above embodiments are merely exemplary embodiments used to illustrate the principles of the present invention, but the present invention is not limited thereto. For those of ordinary skill in the art, various modifications and improvements can be made without departing from the spirit and essence of the present invention, and these modifications and improvements are also considered to be within the scope of protection of the present invention.

Claims

1. A vehicle-mounted power supply circuit, Features : It includes a voltage-limiting overvoltage protection circuit and a voltage-step-down circuit, the voltage-limiting overvoltage protection circuit includes a switch tube and a voltage-limiting overvoltage protection control circuit, the first pole of the switch tube is connected to the input power supply and the positive pole of the diode D3, the negative pole of the diode D3 is connected to the control pole of the switch tube, and the second pole of the switch tube is connected to the input end of the voltage-step-down circuit, the voltage-limiting overvoltage protection control circuit includes a boost circuit and a voltage stabilizing circuit, the boost circuit is used to increase the control pole voltage of the switch tube to a voltage higher than the second pole voltage of the switch tube, and the voltage stabilizing circuit is used to stabilize the control pole voltage of the switch tube at a set value, so that the switch tube is turned on when the input power supply voltage is within the set voltage range.

2. The vehicle-mounted power supply circuit according to claim 1, Features: A resistor R1 is connected in series between the anode of the diode D3 and the first electrode of the switch tube.

3. The vehicle-mounted power supply circuit according to claim 1, Features: The boost circuit includes a capacitor C1, a capacitor C12, a diode D1 and a diode D2, one end of the capacitor C1 is connected to the output end SW of the power chip of the buck circuit, the other end of the capacitor C1 is respectively connected to the positive electrode of the diode D1 and the negative electrode of the diode D2, the positive electrode of the diode D2 is connected to the second electrode of the switch tube, the negative electrode of the diode D1 is connected to the control electrode of the switch tube and one end of the capacitor C12, and the other end of the capacitor C12 is grounded.

4. The vehicle-mounted power supply circuit according to claim 3, Features: A resistor R4 is connected in series between the cathode of the diode D1 and the control electrode of the switch tube.

5. The vehicle-mounted power supply circuit according to claim 1, Features: The voltage stabilizing circuit comprises a voltage stabilizing tube D5, a cathode of the voltage stabilizing tube D5 is connected to a control electrode of the switch tube, and a cathode of the voltage stabilizing tube D5 is grounded.

6. The vehicle-mounted power supply circuit according to claim 1, Features: The step-down circuit is used to step down the input power supply voltage to the required voltage output; the step-down circuit includes a Buck power supply chip, the input end of the Buck power supply chip is respectively connected to the second pole of the switch tube and one end of the resistor R2, the other end of the resistor R2 is respectively connected to one end of the resistor R5 and the EN pin of the Buck power supply chip, the other end of the resistor R5 is grounded, the SW pin of the Buck power supply chip is respectively connected to one end of the resistor R3, the input end of the voltage limiting and overvoltage protection control circuit, one end of the inductor L2 and the negative electrode of the diode D4, the other end of the resistor R3 is connected to one end of the capacitor C2, the other end of the capacitor C2 is connected to the BOOT pin of the Buck power supply chip, the positive electrode of the diode D4 is grounded, the other end of the inductor L2 is respectively connected to one end of the resistor R6 and the output end of the step-down circuit, the other end of the resistor R6 is respectively connected to the FB pin of the Buck power supply chip and one end of the resistor R9, and the other end of the resistor R9 is grounded.

7. The vehicle-mounted power supply circuit according to claim 6, Features: A capacitor C11 is connected in parallel across the resistor R6; and / or, The step-down circuit further includes a capacitor C7, a capacitor C8, and a capacitor C9, one end of the capacitor C7, one end of the capacitor C8, and one end of the capacitor C9 are connected to the input end of the Buck power chip, and the other end of the capacitor C7, the other end of the capacitor C8, and the other end of the capacitor C9 are grounded; and / or, The step-down circuit further includes a capacitor C13, a capacitor C14, and a capacitor C15, one end of the capacitor C13, one end of the capacitor C14, and one end of the capacitor C15 are connected to the output end of the step-down circuit, and the other end of the capacitor C13, the other end of the capacitor C14, and the other end of the capacitor C15 are grounded; and / or, The step-down circuit further includes a capacitor CE1 , one end of the capacitor CE1 is connected to the output end of the step-down circuit, and the other end of the capacitor CE1 is grounded.

8. The vehicle-mounted power supply circuit according to claim 1, Features: It also includes an input filter circuit, wherein the input end of the input filter circuit is connected to the vehicle power supply, and the output end of the input filter circuit is connected to the first pole of the switch tube.

9. The vehicle-mounted power supply circuit according to claim 8, Features: The input filter circuit includes capacitor C3, capacitor C10, inductor L1, capacitor C4, capacitor C6, and capacitor C5. One end of capacitor C3 is connected to one end of inductor L1 and the vehicle power supply, the other end of capacitor C3 is connected to one end of capacitor C10, and the other end of capacitor C10 is grounded. The other end of inductor L1 is respectively connected to one end of capacitor C4, one end of capacitor C6, and one end of capacitor C5, and the other end of capacitor C4, the other end of capacitor C6, and the other end of capacitor C5 are grounded.

10. The vehicle-mounted power supply circuit according to any one of claims 1 to 9, Features: The switch tube is an N-type transistor, the first pole of the switch tube is a D pole, the second pole of the switch tube is an S pole, and the control pole of the switch tube is a G pole.

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