High-voltage constant-current fast insulation test protection circuit

Abstract

The utility model discloses a kind of based on high voltage constant current fast insulation test protection circuit, including high voltage power HV_POWER1, the anode of high voltage power HV_POWER1 is connected to the node of HV_VCC, the cathode of high voltage power HV_POWER1 is connected with HV_GND ground, high voltage power HV_POWER1 is formed with the node of HV_VCC in series through load test resistance Rx1, output control switch SW1, piezoresistive protection resistance R9 and piezoresistive protection resistance R10 and one loop.The constant current protection mode is adopted, when test current exceeds hardware preset value, protection is realized by rapidly reducing output voltage, avoid transient overcurrent security risk, guarantee the stability, safety of test process.High voltage source provides adjustable stable high voltage DC, constant current circuit cooperates with high voltage source, when test current is reasonable, output voltage is similar to high voltage source output, without frequent voltage adjustment, adapt to different test scene needs.

Description

Technical Field

[0001] This utility model relates to the field of constant current protection circuit technology, specifically a high-voltage constant current rapid insulation test protection circuit. Background Technology

[0002] When the resistance value of the voltage divider and current limiting resistor is too large, its equivalent impedance increases significantly. Once an external load resistor is connected, the total impedance of the circuit changes. According to the voltage divider principle, the output voltage will deviate significantly from the theoretical value, seriously affecting the accuracy of the high-voltage insulation test results. If a resistor with a smaller resistance value is selected, the current through the resistor will increase sharply during the high-voltage insulation test. To ensure that the resistor operates normally and is not burned out, the rated power of the resistor needs to be greatly increased. This not only leads to an increase in the size of the resistor and limited installation space, but also significantly increases the procurement cost and the overall cost of the equipment. The large current generated by an excessively small resistance value is very likely to exceed the rated output power and current carrying capacity of the high-voltage power supply. Once exceeded, it will not only cause the power supply to operate under overload, shortening its service life, but may also cause serious safety accidents such as overheating, component damage, or even fire, threatening the lives of test personnel and the stable operation of the equipment. Utility Model Content

[0003] The purpose of this invention is to provide a high-voltage constant current rapid insulation test protection circuit to solve the problems mentioned in the background art.

[0004] This utility model provides the following technical solution: a high-voltage constant current fast insulation test protection circuit, including a high-voltage power supply HV_POWER1, the positive terminal of the high-voltage power supply HV_POWER1 is connected to the node of HV_VCC, the negative terminal of the high-voltage power supply HV_POWER1 is connected to ground with HV_GND, and the high-voltage power supply HV_POWER1 is connected in series with the node of HV_VCC through a load test resistor Rx1, an output control switch SW1, a varistor protection resistor R9 and a varistor protection resistor R10 to form a loop.

[0005] Preferably, two identical single-channel constant current circuits are formed between HV_VCC and the output control switch SW1. In the first single-channel constant current circuit, the drain of MOSFET Q1 is connected to the node of HV_VCC, the source of MOSFET Q1 is connected to one end of resistor R5, and the other end of resistor R5 is connected to the base of transistor Q3. The drain of MOSFET Q1 is also connected to the collector of transistor Q3 through a series branch of resistors R1 and R3. The emitter of transistor Q3 is connected to the cathode of Zener diode ZD1, the anode of Zener diode ZD1 is connected to one end of resistor R7, and the other end of resistor R7 is connected to the node of HV_VCC.

[0006] Preferably, in the second single-channel constant current circuit, the drain of the MOSFET Q2 is connected to the node HV_VCC, the source of the MOSFET Q2 is connected to one end of resistor R6, and the other end of resistor R6 is connected to the base of transistor Q4; the drain of the MOSFET Q2 is connected to the collector of transistor Q4 via a series branch of resistors R2 and R4, the emitter of transistor Q4 is connected to the cathode of Zener diode ZD2, the anode of Zener diode ZD2 is connected to one end of resistor R8, and the other end of resistor R8 is connected to the connection node between the anode of Zener diode ZD1 and resistor R7 in the first channel, so that the two sub-circuits are electrically connected.

[0007] Preferably, the varistor R9 is connected between HV_VCC and the anode of Zener diode ZD1, and the varistor R10 is connected at the relevant node between Zener diode ZD2 and HV_VCC.

[0008] Preferably, the number of single-channel constant current circuits is set to a certain extent, and they are connected in series to increase the test withstand voltage.

[0009] Compared with the prior art, the beneficial effects of this utility model are: 1. Precise constant current protection: Adopting constant current protection mode, when the test current exceeds the hardware preset value, the output voltage is quickly reduced to achieve protection, avoiding instantaneous overcurrent safety hazards and ensuring the stability and safety of the test process.

[0010] 2. High-efficiency voltage adaptation: The high-voltage source provides adjustable and stable high-voltage DC. The constant current circuit works in conjunction with the high-voltage source. When the test current is reasonable, the output voltage is close to that of the high-voltage source, eliminating the need for frequent voltage adjustments and adapting to different test scenario requirements.

[0011] 3. Strong expandability: During testing, multiple constant current module circuits can be stacked to meet high withstand voltage testing requirements. Attached Figure Description

[0012] Figure 1 This is a schematic diagram of the dual-module high-voltage constant current protection circuit of this utility model; Figure 2 This is a schematic diagram of a single module of the high-voltage constant current protection circuit of this utility model. Detailed Implementation

[0013] The technical solutions of the present utility model will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only some embodiments of the present utility model, and not all embodiments. Based on the embodiments of the present utility model, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the protection scope of the present utility model.

[0014] Please see Figure 1-2 This utility model provides a technical solution: a high-voltage constant current rapid insulation test protection circuit, including a high-voltage power supply HV_POWER1. The positive terminal of the high-voltage power supply HV_POWER1 is connected to the node of HV_VCC to provide high-voltage power to the entire circuit. The negative terminal of the high-voltage power supply HV_POWER1 is connected to ground HV_GND as the ground reference terminal of the circuit. The high-voltage power supply HV_POWER1 forms a loop with the node of HV_VCC through the load test resistor Rx1, the output control switch SW1, the varistor protection resistor R9, and the varistor protection resistor R10. The loop can be turned on when SW1 is closed, providing rapid power output for rapid insulation testing.

[0015] Please see Figure 1-2 Two identical single-channel constant current circuits are formed between HV_VCC and the output control switch SW1. Several single-channel constant current circuits are set and connected in series to increase the test withstand voltage.

[0016] Please see Figure 1-2 In the first single-channel constant current circuit, the drain of MOSFET Q1 is connected to the node HV_VCC, the source of MOSFET Q1 is connected to one end of resistor R5, and the other end of resistor R5 is connected to the base of transistor Q3. The drain of MOSFET Q1 is also connected to the collector of transistor Q3 via a series branch of resistors R1 and R3. The emitter of transistor Q3 is connected to the cathode of Zener diode ZD1. The anode of Zener diode ZD1 is connected to one end of resistor R7, and the other end of resistor R7 is connected to the node HV_VCC. A varistor resistor R9 is connected between HV_VCC and the anode of Zener diode ZD1. Please see Figure 1-2 In the second single-channel constant current circuit, the drain of MOSFET Q2 is connected to the node HV_VCC, the source of MOSFET Q2 is connected to one end of resistor R6, and the other end of resistor R6 is connected to the base of transistor Q4. The drain of MOSFET Q2 is connected to the collector of transistor Q4 via a series branch of resistors R2 and R4. The emitter of transistor Q4 is connected to the cathode of Zener diode ZD2. Varistor R10 is connected to the relevant node between Zener diode ZD2 and HV_VCC. The anode of Zener diode ZD2 is connected to one end of resistor R8, and the other end of resistor R8 is connected to the node connecting the anode of Zener diode ZD1 and resistor R7 in the first channel, thus electrically connecting the two sub-circuits.

[0017] The voltage clamping function of the varistor absorbs constant current threshold errors caused by various factors in the circuit components, achieving temperature compensation or overvoltage protection for the circuit and ensuring stable operation under different temperature environments. The overall circuit is centered on a high-voltage power supply, and through two similar and related sub-circuits, in conjunction with varistors, switches, and resistor networks, it forms an insulation rapid testing and protection system with functions such as high-voltage extension adaptation, branch constant current output protection, and temperature adaptation.

[0018] Working principle: Please refer to Figure 1-2 When the output control switch SW1 is closed and the load resistor RX1 is connected to the circuit, the circuit will undergo a complete working process from dynamic transition to stability. The current changes and device functions at each stage are as follows: At the instant of connection (timescale can be microseconds or even shorter), the active devices in the circuit (such as MOSFETs Q1 and Q3) have not yet responded, and the capacitors are in the initial charging state. At this time, the entire circuit can be simplified to a purely resistive network consisting of the high-voltage power supply HV_VCC and multiple series resistors. The current path is as follows: HV_VCC flows through the current-limiting resistors R7 and R8 in sequence, then through the load resistor RX1, and finally returns to HV_GND. The instantaneous output current Iout in this stage completely follows Ohm's law, and its magnitude can be approximately expressed as Iout≈HV_VCC / (R7+R8+RX1). Since R7 and R8 are megaohm (MΩ) high-resistance resistors, they form a very large total resistance after being connected in series with the load resistor RX1. Even if the HV_VCC voltage is high, the initial inrush current is limited to an extremely small level, effectively suppressing current spikes in the circuit while rapidly connecting the load for testing, playing a crucial initial buffering and protection role.

[0019] With the initial small current established, the circuit enters the startup phase. Current flows through the sampling resistor (e.g., R1) of the constant current module. When the voltage drop across R1 reaches the turn-on threshold of the control transistor (e.g., Q2), the negative feedback mechanism of the constant current module starts. After Q2 turns on, it adjusts the gate voltage of the regulating transistor (e.g., Q1), gradually transitioning it from a fully conducting state to a constant current state. The two-stage series-connected constant current module sequentially completes this startup process, achieving a controlled increase in current.

[0020] Once the constant current module is fully established, the circuit enters the steady-state phase. At this point, the constant current module becomes the dominant factor in the loop, precisely clamping the total current to a set constant value through a negative feedback mechanism (this value is determined by parameters such as the sampling resistor value and the MOSFET threshold voltage). The current flowing through the load resistor RX1 is no longer determined by the total resistance of R7, R8, and the load resistor RX1, but is strictly controlled by the constant current module; excess voltage in the loop (i.e., HV_VCC minus the total voltage drop across the constant current module and RX1) is mainly applied to the current-limiting resistors R7 and R8 and the regulating transistor of the constant current module to ensure current stability.

[0021] During the entire startup process, especially when transitioning from the pure resistive current-limiting stage to the constant current stage, there may be a slight difference in the response speed of the two constant current modules. This could cause one of the modules to experience excessively high voltage. At this time, the varistor R9 and R10 connected in parallel in the module will monitor the voltage across them in real time. Once the voltage exceeds their clamping threshold, the resistance will decrease rapidly and conduct, absorbing the excess current, thereby balancing the voltage distribution and ensuring that each constant current module can smoothly and safely enter the normal operating state, avoiding damage due to overvoltage.

[0022] In summary, at the instant the load resistor RX1 is connected, the circuit's operating state switches sequentially: momentarily, it exhibits pure resistance, with the current determined by Iout≈HV_VCC / (R7+R8+RX1), and the megaohm-level R7 and R8 limiting the inrush current; subsequently, in a millisecond-level transition, the constant current module starts, the negative feedback mechanism takes over, and the current rises to the set value under control; finally, it enters a steady state, and the output current stabilizes at a constant value. Throughout this process, especially during state switching, the varistor effectively absorbs the transient overvoltage caused by module differences, which is crucial for ensuring system reliability and allowing for voltage adaptation through multi-module expansion.

[0023] In the schematic diagram of a single constant current circuit module, HV_IN represents the high-voltage positive input, and HV_OUT represents the high-voltage positive output. During testing, this circuit needs to be connected in series with the high-voltage circuit to achieve constant current protection. Its core constant current protection mainly consists of transistors, high-voltage MOSFETs, and resistors.

[0024] Constant current protection: R7 is a high-voltage voltage divider and current-limiting resistor (megaohm level resistor is recommended), mainly providing the gate voltage for Q1. ZD1 is responsible for stabilizing the gate voltage within a suitable range. Initially, the output current is mainly provided by the current-limiting resistor R7. Due to the large size of this resistor, the output current is... Then, the voltage is gradually increased to enter a constant current state. In the circuit, R1 determines the magnitude of the constant current. R1 collects the output current of Q1 and feeds it back to the base of transistor Q3 via R3 to control the feedback Q1 for closed-loop constant current output. If the maximum voltage is 0.7V, then the output constant current voltage is: .

[0025] Rated test voltage: In high-voltage testing, the constant current of this circuit is mainly determined by the withstand voltage of Q1. The higher the withstand voltage of Q1, the higher the voltage that can be tested. Under extremely high voltage conditions, where the withstand voltage of conventional MOSFETs is insufficient, when implementing multiple constant current protection circuits in series to improve the operating withstand voltage, each module needs to be connected in parallel with a varistor for voltage limiting protection to prevent excessive error in the constant current resistor, which could lead to uneven voltage distribution and damage to the module.

Claims

1. A high-voltage constant current rapid insulation test protection circuit, comprising a high-voltage power supply HV_POWER1, characterized in that: The positive terminal of the high-voltage power supply HV_POWER1 is connected to the node of HV_VCC, and the negative terminal of the high-voltage power supply HV_POWER1 is connected to ground with HV_GND. The high-voltage power supply HV_POWER1 forms a loop in series with the node of HV_VCC through the load test resistor Rx1, the output control switch SW1, the varistor protection resistor R9, and the varistor protection resistor R10.

2. The high-voltage constant current rapid insulation test protection circuit according to claim 1, characterized in that: The HV_VCC and the output control switch SW1 form two identical single-channel constant current circuits. In the first single-channel constant current circuit, the drain of the MOSFET Q1 is connected to the node of HV_VCC, the source of the MOSFET Q1 is connected to one end of resistor R5, and the other end of resistor R5 is connected to the base of transistor Q3. The drain of the MOSFET Q1 is also connected to the collector of transistor Q3 through a series branch of resistors R1 and R3. The emitter of transistor Q3 is connected to the cathode of Zener diode ZD1, the anode of Zener diode ZD1 is connected to one end of resistor R7, and the other end of resistor R7 is connected to the node of HV_VCC.

3. The high-voltage constant current rapid insulation test protection circuit according to claim 2, characterized in that: In the second single-channel constant current circuit, the drain of MOSFET Q2 is connected to the node HV_VCC, the source of MOSFET Q2 is connected to one end of resistor R6, and the other end of resistor R6 is connected to the base of transistor Q4; the drain of MOSFET Q2 is connected to the collector of transistor Q4 via a series branch of resistors R2 and R4, the emitter of transistor Q4 is connected to the cathode of Zener diode ZD2, the anode of Zener diode ZD2 is connected to one end of resistor R8, and the other end of resistor R8 is connected to the connection node between the anode of Zener diode ZD1 and resistor R7 in the first channel, so that the two sub-circuits are electrically connected.

4. The high-voltage constant current rapid insulation test protection circuit according to claim 3, characterized in that: The varistor R9 is connected between HV_VCC and the anode of Zener diode ZD1, and the varistor R10 is connected at the relevant node between Zener diode ZD2 and HV_VCC.

5. The high-voltage constant current rapid insulation test protection circuit according to claim 2, characterized in that: Several single-channel constant current circuits are set up, and they are connected in series to increase the test withstand voltage.

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