PCB insulation impedance flying probe test circuit

Abstract

The utility model relates to a PCB insulation impedance flying probe test circuit, which is used for testing insulation impedance of a PCB tested unit and comprises an access circuit, an amplifying circuit and a measuring circuit, the access circuit comprises a power supply, an accompanying resistor and a grounding resistor, the tested unit and the accompanying resistor are connected in parallel to form a parallel circuit, a first end of the parallel circuit is connected with an output end of the power supply, and a second end of the parallel circuit is connected with an output end of the grounding resistor. The second end is connected with the amplifying circuit and is connected with the grounding resistor, and the output end of the amplifying circuit is connected with the measuring circuit. According to the utility model, the parallel accompanying test resistors are added in the access circuit, a parallel resistor working mode is adopted, and the tested unit and the known accompanying test resistor are connected in parallel, so that the channel test current is improved, the stability of test parameters is improved, the current output by the amplifying circuit is in a smaller interval range, and the accurate detection of the measuring circuit is facilitated.

Description

TECHNICAL FIELD

[0001] The utility model belongs to the field of flying probe test, concretely relates to a PCB insulation impedance flying probe test circuit. BACKGROUND

[0002] The flying probe tester is equipped with multiple groups of mechanical arms with telescopic test probes, during testing, the computer controls the probe movement according to the preset program, the probe contacts the solder pad, via hole or component pin of the PCB point by point, and the electrical parameters such as resistance, capacitance, voltage and current are measured.

[0003] Among them, when testing the insulation impedance between the adjacent insulation conductor grids of the PCB, a pair of flying probes is generally used for testing in the prior art, the flying probes are placed between the grids and high voltage is applied, the signal is detected through the amplification circuit, and the output electrical signal is decoded to judge the leakage current, and the existing defects are that the current difference between leakage and non-leakage is large, and the range to be detected after the amplification circuit is larger, which is not conducive to accurate detection. UTILITARIAN CONTENT

[0004] The utility model aims at solving the above -mentioned problem and provides a PCB insulation impedance flying probe test circuit.

[0005] The utility model realizes the above-mentioned purpose through the following technical schemes:

[0006] A PCB insulation impedance flying probe test circuit is used for testing the insulation impedance of the measured unit of the PCB, comprising an access circuit, an amplification circuit and a measurement circuit, the access circuit comprises a power supply, a test resistance and a grounding resistance, wherein the measured unit is connected in parallel with the test resistance to form a parallel circuit, the first end of the parallel circuit is connected with the output end of the power supply, the second end is connected with the amplification circuit and the grounding resistance, and the output end of the amplification circuit is connected with the measurement circuit.

[0007] As a further optimization scheme of the utility model, the amplification circuit is a multistage amplification circuit, comprising a first amplifier and a second amplifier arranged in series, and the scheme further increases the readability of the collected signal by using a multistage precision amplifier to process the collected signal.

[0008] As a further optimization scheme of the utility model, the output end of the first amplifier is connected with the measurement circuit, the output end of the second amplifier is connected with the input end of the first amplifier, and the second end of the parallel circuit is connected with the input end of the second amplifier.

[0009] As a further optimization scheme of the utility model, the model of the second amplifier is AD8421, the amplifier is a low-noise instrument amplifier, has the advantages of low cost, low power consumption, extremely low noise, ultra-low bias current and high-speed instrument amplifier, and is suitable for measuring low-level signals.

[0010] As a further optimization scheme of the utility model, the power supply VEE adopts high-voltage high-speed solid-state relay and dry reed relay to discharge, prevents residual charge from influencing test result.

[0011] As a further optimization scheme of the utility model, the measuring circuit includes SPI communication digital potentiometer, uses SPI communication digital potentiometer scheme adjustment control for the operational amplifier gain generated by amplification circuit, uses analog-digital conversion chip 12-bit ADC conversion output for the signal collected to FPGA decoding.

[0012] The utility model has the advantages that:

[0013] The utility model discloses a kind of test circuits for PCB insulation impedance, including access circuit, amplification circuit and measuring circuit, access circuit includes power supply VEE, test resistance R2 and ground resistance R3, wherein, measured unit R1 and test resistance R2 are connected in parallel to form parallel circuit, the first end of parallel circuit is connected with the output end of power supply VEE, the second end is connected with ground resistance R3 in amplification circuit B, and the output end of amplification circuit B is connected with measuring circuit C. BRIEF DESCRIPTION OF DRAWINGS

[0014] Figure 1 It is the circuit schematic diagram of the utility model.

[0015] In the drawing: A, access circuit;VEE, power supply;R1, measured unit;R2, test resistance;R3, ground resistance;

[0016] B, amplification circuit;U1, first amplifier;U2, second amplifier;

[0017] C, measuring circuit;V, potentiometer. DETAILED DESCRIPTION

[0018] The following detailed description of the application in conjunction with the drawings, it is necessary to point out here that the following detailed description is only used to further illustrate the application, can not be understood as limiting the scope of the application, the skilled person in the art can make some non-essential improvements and adjustments to the application according to the above application.

[0019] Example 1

[0020] As Figure 1 As shown in a kind of PCB insulation impedance flying probe test circuit, for testing the insulation impedance of PCB measured unit R1, including access circuit A, amplification circuit B and measuring circuit C, access circuit A includes power supply VEE, test resistance R2, ground resistance R3, wherein, measured unit R1 and test resistance R2 are connected in parallel to form parallel circuit, the first end of parallel circuit is connected with the output end of power supply VEE, the second end is connected with ground resistance R3 in amplification circuit B, and the output end of amplification circuit B is connected with measuring circuit C.

[0021] The power supply VEE adopts high-voltage high-speed solid-state relays and dry reed relays for discharging to prevent residual charge from affecting the test results, applies high voltage (usually DC 30V-500V), and calculates the insulation impedance value by measuring the voltage converted by the leakage current. The test resistance R2 and the grounding resistance R3 used are high-precision resistances with an accuracy of ≤1%.

[0022] Formula: Insulation impedance = V applied high voltage / I leakage current, current uA level.

[0023] In this scheme, the test resistance R2 is added in parallel in the access circuit A, and a parallel resistance working mode is adopted, the measured unit R1 and the known test resistance R2 are connected in parallel, which is used to improve the test current of the channel and increase the stability of the test parameters.

[0024] Further, the amplification circuit B is a multi-stage amplification circuit, including a first amplifier U1 and a second amplifier U2 connected in series, and the scheme further increases the readability of the collected signals by using multi-stage precision amplifiers to process the collected signals. The model of the first amplifier U1 can be LM741, and the model of the second amplifier U2 is AD8421. The AD8421 amplifier is a low-noise instrument amplifier with the advantages of low cost, low power consumption, extremely low noise, and ultra-low bias current, which is suitable for measuring low-level signals.

[0025] The output end of the first amplifier U1 is connected with the measurement circuit C, the output end of the second amplifier U2 is connected with the non-inverting input end of the first amplifier U1, and the second end of the parallel circuit is connected with the non-inverting input end of the second amplifier U2. The non-inverting input end of the LM741 amplifier is pin 3, and the output end is pin 6. The non-inverting input end of the AD8421 amplifier is pin 4, and the output end is pin 7.

[0026] The measurement circuit C includes an SPI communication digital potentiometer. The SPI communication digital potentiometer V scheme is used to adjust and control the operational amplifier gain generated by the amplification circuit B, and the collected signals are converted and output to the FPGA decoder by using a 12-bit ADC conversion chip.

[0027] The implementation specifically is that: the circuit can simultaneously set multiple flying needles to detect multiple points on the PCB. The voltage signal at the second end of the parallel circuit is amplified by the amplification circuit and detected by the potentiometer V, the current leakage condition is obtained by analyzing the voltage signal, and the threshold value is set according to the actual situation. When the threshold value is reached, it is determined that leakage occurs. The grounding resistance R3 is used for discharging static electricity.

[0028] The above-described embodiments only express several implementation manners of the present application, and the description is relatively specific and detailed, but it should not be understood as a limitation on the patent scope of the present application. It should be noted that, for ordinary skilled persons in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, which all belong to the protection scope of the present application.

Claims

1. A PCB insulation impedance flying probe test circuit for testing the insulation impedance of a PCB unit under test (R1), comprising an access circuit (A), an amplification circuit (B) and a measurement circuit (C), characterized in that: The access circuit (A) comprises a power supply (VEE), a test resistance (R2), a grounding resistance (R3), wherein the measured unit (R1) is connected in parallel with the test resistance (R2) to form a parallel circuit, the first end of the parallel circuit is connected with the output end of the power supply (VEE), the second end is connected with the grounding resistance (R3) and is connected with an amplification circuit (B), and the output end of the amplification circuit (B) is connected with a measurement circuit (C).

2. The PCB insulation impedance flying probe test circuit of claim 1, wherein: The amplification circuit (B) is a multi-stage amplification circuit, comprising a first amplifier (U1) and a second amplifier (U2) connected in series.

3. The PCB insulation impedance flying probe test circuit of claim 2, wherein: The output end of the first amplifier (U1) is connected with the measurement circuit (C), the output end of the second amplifier (U2) is connected with the input end of the first amplifier (U1), and the second end of the parallel circuit is connected with the input end of the second amplifier (U2).

4. The PCB insulation impedance flying probe test circuit of claim 2, wherein: The model of the second amplifier (U2) is AD8421.

5. The PCB insulation impedance flying probe test circuit of claim 1, wherein: The power supply (VEE) adopts a high-voltage high-speed solid-state relay and a reed relay for discharging.

6. The PCB insulation impedance flying probe test circuit of claim 1, wherein: The measurement circuit (C) comprises an SPI communication digital potentiometer (V).

Images