A protection circuit of capacitive current limiting

Abstract

This utility model relates to the field of vehicle-mounted step-down power supply technology, specifically to a capacitor current-limiting protection circuit, including a PWM controller, a planar coil inductor, a field-effect transistor (FET), a dual-channel FET, a second resistor, a capacitor, and a first resistor. The first terminal of the PWM controller is connected to the FET, and the side terminal of the FET is connected to the planar coil inductor. In this utility model, the charging speed of the capacitor through the resistor is equal to the inductor current growth rate, thereby limiting the voltage across the capacitor to the maximum peak current of the inductor. The maximum output power is proportional to the product of the input voltage and the peak inductor current, thus limiting the maximum output power and achieving the function of output load current-limiting protection. This invention has advantages such as small size, precise and adjustable current limiting value, low power consumption, and good electromagnetic compatibility, improving the reliability of the step-down power supply, extending its service life, and reducing production costs.

Description

Technical Field

[0001] This utility model relates to the field of vehicle-mounted step-down power supply technology, specifically to a capacitor current-limiting protection circuit. Background Technology

[0002] A high-power DC-DC step-down power supply for vehicles is a high-power power electronic device installed in a vehicle that can convert the vehicle's high-voltage DC power (such as a power battery) into a low-voltage DC power. Its core function is "step-down + power conversion", which supplies power to the vehicle's low-voltage electrical equipment or charges the low-voltage battery. It is a key component in the power system of new energy vehicles (especially pure electric and plug-in hybrid models).

[0003] Currently, commercially available high-power DC-DC step-down power supplies for vehicles achieve current limiting protection by sampling the voltage of the power resistor at the output end. However, due to the large size of the power resistor for current limiting, the current limiting value generally not exceeding 10A, high power consumption, and poor electromagnetic compatibility, its practicality is insufficient, and therefore it still has shortcomings.

[0004] In conclusion, it is necessary to invent a capacitor current-limiting protection circuit. Utility Model Content

[0005] To address this issue, this invention provides a capacitor current-limiting protection circuit to solve the problem that current commercially available high-power vehicle DC-DC step-down power supplies are not practical due to their large size required for power resistor current limiting, current limiting values ​​generally not exceeding 10A, high power consumption, and poor electromagnetic compatibility.

[0006] To achieve the above objectives, this utility model provides the following technical solution: a capacitor current limiting protection circuit, comprising a PWM controller, a planar coil inductor, a field-effect transistor, a dual-channel field-effect transistor, a second resistor, a capacitor, and a first resistor; The first end of the PWM controller is connected to a field-effect transistor (FET), the side end of the FET is connected to a planar coil inductor, the source of the FET is connected to the end of a dual-channel FET, and the other end of the PWM controller is connected to the common terminal of a second resistor, a capacitor, and a first resistor.

[0007] Preferably, the third terminal of the PWM controller is connected to a high potential (VIN), and the second terminal of the PWM controller is connected to the gate of the dual-channel field-effect transistor.

[0008] Preferably, one end of the planar coil inductor is connected to a high potential (VIN), and the other end of the planar coil inductor is connected to the drain of the field-effect transistor.

[0009] Preferably, the drain of the dual-channel field-effect transistor is connected to the source of the field-effect transistor, and the source of the dual-channel field-effect transistor is connected to one end of the second resistor.

[0010] Preferably, the other end of the second resistor is connected to the positive terminal of the capacitor, the negative terminal of the capacitor is connected to one end of the first resistor, and the other end of the first resistor is connected to a high potential (VIN).

[0011] The beneficial effects of this utility model are: In this invention, the charging speed of the capacitor through the resistor is equal to the growth rate of the inductor current. This limits the voltage across the capacitor to the maximum peak current of the inductor. The maximum output power is proportional to the product of the input voltage and the peak inductor current, thus limiting the maximum output power and providing output load current limiting protection. This invention has advantages such as small size, precisely adjustable current limiting value, low power consumption, and good electromagnetic compatibility. It improves the reliability of the step-down power supply, extends its service life, and reduces production costs. Attached Figure Description

[0012] Figure 1 This is a schematic diagram of the circuit structure of a capacitor current-limiting protection circuit in this utility model; Figure 2 This is a schematic diagram of the DC-DC step-down circuit board in this utility model; Figure 3 This is a schematic diagram of the switch control circuit board in this utility model; Figure 4 This is a schematic diagram of the main control circuit board in this utility model; Figure 5 This is a schematic diagram of the specific structure of the capacitor current limiting protection circuit in this utility model.

[0013] In the diagram: 1. PWM controller; 2. Planar coil inductor; 3. Field-effect transistor; 4. Dual field-effect transistor; 5. Second resistor; 6. Capacitor; 7. First resistor; 8. Output harness; 9. Switch control circuit board; 10. DC-DC step-down circuit board; 11. Main control circuit board. Detailed Implementation

[0014] The preferred embodiments of the present invention will be described below with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0015] See attached document Figures 1-5This utility model provides a capacitor current limiting protection circuit, including a PWM controller 1, a planar coil inductor 2, a field-effect transistor 3, a dual-channel field-effect transistor 4, a second resistor 5, a capacitor 6, and a first resistor 7. The first end of the PWM controller 1 is connected to the field-effect transistor 3. Specifically, the PWM controller 1 is small in size, low in power consumption, high efficiency, large duty cycle, and low frequency. In the circuit, it plays the role of outputting PWM signal control, directly controlling and driving the field-effect transistor 3 and the dual-channel field-effect transistor 4. The side end of the field-effect transistor 3 is connected to the planar coil inductor 2. The planar coil inductor 2 is small in size, has a large inductance, and a large saturation current. In the circuit, it plays the role of providing output load driving capability. The source of the field-effect transistor 3 is connected to the end of the dual-channel field-effect transistor 4. The other end of the PWM controller 1 is connected to the common terminal of the second resistor 5, the capacitor 6, and the first resistor 7. The third end of the PWM controller 1 is connected to a high potential (VIN). The second end of the PWM controller 1 is connected to the gate of the dual-channel field-effect transistor 4. One end of the planar coil inductor 2 is connected to the high potential (VIN), and the other end is connected to the drain of the field-effect transistor 3. The drain of the dual-channel field-effect transistor 4 is connected to the source of the field-effect transistor 3. The dual-channel field-effect transistor 4, with its small surface-mount package, low internal resistance, and fast switching speed, functions to control the power supply and current limit of the PWM controller. The source of the dual-channel field-effect transistor 4 is connected to one end of the second resistor 5, and the other end of the second resistor 5 is connected to the positive terminal of the capacitor 6. The negative terminal of the capacitor 6 is connected to one end of the first resistor 7, and the other end of the first resistor 7 is connected to the high potential (VIN). The second resistor 5 is connected between the source of the dual-channel field-effect transistor 4 and the capacitor 6, forming part of an RC circuit. The capacitor 6 acts as a current-limiting detection element, and its voltage is proportional to the maximum peak current of the inductor 2 (Vc = Imax × ...). R7), forming the core of capacitor current limiting protection, the first resistor 7 is set as the key resistor of current limiting protection, and together with capacitor 6, they form an RC circuit. Its resistance value determines the charging rate of capacitor 6. The second resistor 5, capacitor 6 and the first resistor 7 together form a current limiting detection circuit. When the voltage on capacitor 6 reaches the preset threshold, the current limiting protection mechanism is triggered. The principle of the entire circuit is as follows: 1. Normal working status PWM controller 1 generates PWM signals to control the on and off states of MOSFET 3 and dual-channel MOSFET 4.

[0016] When the field-effect transistor 3 is turned on, the current flows from VIN through the planar coil inductor 2 to the field-effect transistor 3, and the planar coil inductor 2 stores energy.

[0017] When the field-effect transistor 3 is turned off, the current in the planar coil inductor 2 flows to the load through the freewheeling diode (not explicitly shown in the figure).

[0018] 2. Traffic limiting protection mechanism Relationship between inductor current and capacitor voltage: The current growth rate of the planar coil inductor 2 matches the charging rate of the RC circuit composed of resistor 7 and capacitor 6.

[0019] The voltage across capacitor 6 is proportional to the maximum peak current of planar coil inductor 2 (Vc = Imax × R7).

[0020] Rate limiting triggering process: As the output load current increases, the current growth rate of the planar coil inductor 2 accelerates.

[0021] The charging speed of capacitor 6 matches the growth rate of the inductor current, and the voltage on capacitor 6 increases accordingly.

[0022] When the voltage on capacitor 6 reaches the preset threshold, the current limiting protection mechanism is triggered.

[0023] Protective actions: PWM controller 1 immediately shuts off the PWM signal output.

[0024] The MOSFET 3 is cut off, stopping the power supply to the load.

[0025] The dual-channel MOSFET 4 is turned on, switching the circuit to protection mode.

[0026] Limit the output current to prevent overcurrent damage to the circuit.

[0027] 3. Mathematical description of the current limiting protection principle Voltage across capacitor 6: Vc = Imax × R7 Inductor current growth rate: di / dt = V / L Capacitor charging rate: dVc / dt = (Vin - Vc) / R7C6 When dVc / dt = di / dt, Vc is proportional to Imax. Maximum output power: Pmax = Vin × Imax Since Vc is proportional to Imax, Pmax is also proportional to Vin and Vc. By controlling the threshold of Vc, the maximum output power can be precisely controlled. Specifically, the instruction manual is attached. Figure 5 This is a detailed circuit diagram. The main control circuit board 11 can install the DC-DC step-down circuit board 10. The switch control circuit board 9 can control the operation of the DC-DC step-down circuit board 10 and the main control circuit board 11. The output wiring harness 8 is used to supply power to the switch control circuit board 9, the DC-DC step-down circuit board 10 and the main control circuit board 11.

[0028] The usage process of this utility model is as follows: Those skilled in the art can first assemble the device according to the above description, then connect all electrical equipment to an external power supply, and control the operation of the device through an external controller. The control programs of all electrical equipment are edited by the production personnel in advance before production. This utility model does not make any technical improvements here, but only assumes that it can normally meet the needs of personnel. The charging speed of capacitor 6 through resistor 7 is equal to the rate of increase of current in planar coil inductor 7. The voltage of capacitor 6 is proportional to the maximum peak current of planar coil inductor 7, thus limiting the maximum peak current. The maximum output power is proportional to the product of input voltage and peak current, thus limiting the maximum output power. When the output power exceeds the peak current of planar coil inductor 7, PWM controller 1 immediately shuts off the PWM signal output, MOSFET 3 is cut off, and dual MOSFET 4 is turned on, thereby achieving the current limiting protection function of the buck power supply, extending the service life of the buck power supply, and reducing production costs.

[0029] The above description is merely a preferred embodiment of this utility model. Any person skilled in the art may modify this utility model or modify it into an equivalent technical solution using the technical solutions described above. Therefore, any simple modifications or equivalent substitutions made based on the technical solutions of this utility model are within the scope of protection claimed by this utility model.

Claims

1. A capacitively limited protection circuit, characterized by: It includes a PWM controller (1), a planar coil inductor (2), a field-effect transistor (3), a dual-channel field-effect transistor (4), a second resistor (5), a capacitor (6), and a first resistor (7); The first end of the PWM controller (1) is connected to a field-effect transistor (3), the side end of the field-effect transistor (3) is connected to a planar coil inductor (2), the source of the field-effect transistor (3) is connected to the end of a dual-channel field-effect transistor (4), and the other end of the PWM controller (1) is connected to the common terminal of a second resistor (5), a capacitor (6) and a first resistor (7).

2. A capacitance-limited protection circuit according to claim 1, characterized in that: The third terminal of the PWM controller (1) is connected to a high potential (VIN), and the second terminal of the PWM controller (1) is connected to the gate of the dual field-effect transistor (4).

3. A capacitance-limited protection circuit according to claim 1, characterized in that: One end of the planar coil inductor (2) is connected to a high potential (VIN), and the other end of the planar coil inductor (2) is connected to the drain of the field-effect transistor (3).

4. The capacitance-limited protection circuit of claim 1, wherein: The drain of the dual-channel field-effect transistor (4) is connected to the source of the field-effect transistor (3), and the source of the dual-channel field-effect transistor (4) is connected to one end of the second resistor (5).

5. A capacitance-current limited protection circuit according to claim 4, characterized in that: The other end of the second resistor (5) is connected to the positive terminal of the capacitor (6), the negative terminal of the capacitor (6) is connected to one end of the first resistor (7), and the other end of the first resistor (7) is connected to the high potential (VIN).

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