A fixture contact reliability detection circuit for lithium battery testing

Abstract

The present invention provides a fixture contact reliability detection circuit for lithium battery testing in the technical field of lithium battery testing equipment, comprising an excitation module, a sampling module, an interface module and a power supply module; the excitation module comprises a self-excited oscillation unit, a bandpass filter unit and an AC constant current source; the sampling module comprises an AC small signal sampling unit, a comparison unit, a low-pass filter unit and a pulse detection unit; the interface module comprises an enabling unit and an output unit. The advantages of the present invention are: the accuracy of fixture contact reliability detection is greatly improved, and the detection cost is reduced.

Description

Technical Field

[0001] The invention relates to the technical field of lithium battery testing equipment, and in particular to a fixture contact reliability detection circuit for lithium battery testing. Background Art

[0002] When testing lithium batteries, a four-terminal wiring method is usually used to connect the test equipment and the lithium battery to be tested to reduce the impact of the excitation circuit current on the measurement results. Ideally, the excitation line and sampling line of the same polarity of the lithium battery are considered to be of equal potential, and the impedance between them can be ignored. However, due to factors such as rust on the wiring body, incomplete pressing of the test fixture or test pin on the surface of the wiring body, the signal collected by the sampling circuit has serious deviations and cannot be distinguished from the influence caused by the characteristics of the lithium battery itself. In high-power testing situations, it may even cause hazards such as overheating and fire. Therefore, during the lithium battery testing process, it is necessary to judge the reliability of the contact of the test fixture to eliminate the interference of other factors other than the characteristics of the lithium battery itself on the measurement, and avoid safety hazards.

[0003] Traditionally, there are two methods for testing the contact reliability of the fixture during lithium battery testing: one is the resistance thermal effect method, which relies on thermal imaging equipment such as infrared thermal imagers. The detection resolution decreases as the number of targets in the field of view increases. It is expensive and difficult to distinguish the disconnection situation on the micro-power test line; the other is the voltage drop method, which requires the intervention of a high-precision ADC and is accompanied by complex software control. In some harsh application scenarios, the collected DC signal is easily affected by strong electromagnetic interference, which poses a challenge to the stability and effectiveness of the test.

[0004] Therefore, how to provide a fixture contact reliability detection circuit for lithium battery testing to improve the accuracy of fixture contact reliability detection and reduce detection costs has become a technical problem that needs to be solved urgently. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a fixture contact reliability detection circuit for lithium battery testing, so as to improve the accuracy of fixture contact reliability detection and reduce detection costs.

[0006] The present invention is implemented as follows: A fixture contact reliability detection circuit for lithium battery testing includes an excitation module, a sampling module, an interface module and a power module;

[0007] The excitation module includes a self-excited oscillation unit, a bandpass filter unit and an AC constant current source; the sampling module includes an AC small signal sampling unit, a comparison unit, a low-pass filter unit and a pulse detection unit; the interface module includes an enabling unit and an output unit;

[0008] The input end of the bandpass filter unit is connected to the output end of the self-excited oscillation unit, and the output end is connected to the input end of the AC constant current source; the input end of the comparison unit is connected to the output end of the AC small signal sampling unit, and the output end is connected to the input end of the low-pass filter unit; the input end of the pulse detection unit is connected to the output end of the low-pass filter unit, and the output end is connected to the output unit; the enabling unit is connected to the AC constant current source and the AC small signal sampling unit respectively;

[0009] The power supply module is respectively connected to the self-excited oscillation unit, the AC constant current source, the AC small signal sampling unit, the comparison unit, the low-pass filtering unit, the pulse detection unit, the enabling unit and the output unit.

[0010] Further, the self-excited oscillation unit includes an operational amplifier U3A, a resistor R3, a resistor R4, a resistor R11, a resistor R21, a capacitor C9 and a capacitor C10;

[0011] Pin 1 of the operational amplifier U3A is connected to capacitor C9, resistor R21 and a bandpass filter unit, pin 2 is connected to resistor R11 and resistor R21, pin 3 is connected to resistor R3, resistor R4 and capacitor C10, and pins 4 and 8 are connected to a power module; the resistor R4 is connected to capacitor C9; the resistor R3 is connected to capacitor C10 and is grounded; the resistor R11 is grounded.

[0012] Further, the bandpass filter unit includes a resistor R6, a resistor R7, a resistor R19, a capacitor C11, a capacitor C13 and a capacitor C14;

[0013] One end of the resistor R6 is connected to the self-excited oscillation unit, and the other end is connected to the resistor R7 and the capacitor C13; one end of the capacitor C14 is connected to the resistor R7 and the capacitor C11, and the other end is connected to the capacitor C13 and the resistor R19 and grounded; the resistor R19 is connected to the capacitor C11 and the AC constant current source.

[0014] Further, the AC constant current source includes an operational amplifier U2B, an operational amplifier U3B, an operational amplifier U4A, a resistor R1, a resistor R2, a resistor R5, a resistor R8, a resistor R9, a resistor R10, a resistor R20, an electrostatic protection circuit D2 and an electrostatic protection circuit D3;

[0015] Pin 5 of the operational amplifier U3B is connected to the bandpass filter unit, and pins 6 and 7 are connected to resistor R10; pin 1 of the operational amplifier U4A is connected to resistor R8, pin 2 is connected to resistor R10 and resistor R20, pin 3 is connected to resistor R5 and resistor R2, and pins 4 and 8 are connected to the power module; pin 5 of the operational amplifier U2B is connected to resistor R1 and electrostatic protection circuit D2, and pins 6 and 7 are connected to resistor R2; one end of the resistor R9 is connected to resistor R8, electrostatic protection circuit D3 and resistor R20, and the other end is connected to resistor R1, resistor R18 and an enabling unit.

[0016] Further, the AC small signal sampling unit includes an instrument amplifier U6, a resistor R24, a resistor R28, a resistor R33 and a capacitor C16;

[0017] Pin 1 of the instrument amplifier U6 is connected to resistor R24 ​​and capacitor C16, pin 2 is connected to one end of resistor R28, pin 3 is connected to the other end of resistor R28, pin 4 is connected to capacitor C18 and resistor R33, pins 5 and 8 are connected to the power module, and pin 7 is connected to the comparison unit; the capacitor C16 and capacitor C18 are both connected to the enabling unit.

[0018] Further, the comparison unit includes an operational amplifier U7A, a resistor R26, a resistor R27, a resistor R30, a capacitor C15 and a capacitor C17;

[0019] One end of the resistor R26 is connected to the AC small signal sampling unit, and the other end is connected to the resistor R27 and the capacitor C15; pins 1 and 2 of the operational amplifier U7A are connected to the resistor R30 and the capacitor C15, pin 3 is connected to the resistor R27 and the capacitor C17, and pins 4 and 8 are connected to the power module; the resistor R30 is connected to the low-pass filter unit.

[0020] Further, the low-pass filter unit includes an operational amplifier U7B, a resistor R25, a resistor R29, a resistor R31, a resistor R34, a resistor R35, a capacitor C20 and a diode D5;

[0021] Pin 5 of the operational amplifier U7B is connected to resistors R25, R34, R35 and capacitor C20, pin 6 is connected to the comparison unit, and pin 7 is connected to resistors R29, R31 and R25; the resistors R34 and R29 are both connected to the power module; the resistor R31 is connected to the output end of the diode D5 and the pulse detection unit.

[0022] Further, the pulse detection unit includes an inverter U8, a diode D4, a resistor R32 and a capacitor C19;

[0023] Pin 1 of the inverter U8 is connected to the low-pass filter unit, pin 2 is grounded, pin 3 is connected to the output end of the resistor R32, the capacitor C19 and the diode D4, pin 4 is connected to the output unit, pin 5 is connected to the power module, and pin 6 is connected to the input end of the diode D4.

[0024] Further, the enabling unit includes a relay K1, a diode D1, a transistor Q1, a resistor R15, a resistor R16, a resistor R17 and a capacitor C12;

[0025] Pin 1 of the relay K1 is connected to the input end of the diode D1 and the c-pole of the transistor Q1, pins 3 and 4 are connected to the AC small signal sampling unit, pins 5 and 6 are connected to the AC constant current source, and pin 8 is connected to the resistor R15, the capacitor C12 and the output end of the diode D1; the e-pole of the transistor Q1 is connected to the resistor R16 and grounded, and the b-pole is connected to the resistor R16 and the resistor R17; the resistor R15 is connected to the power module.

[0026] Further, the output unit includes an optical coupler U5, a resistor R12, a resistor R13 and a resistor R14;

[0027] Pin 1 of the optocoupler U5 is connected to resistors R12 and R13, pin 2 is connected to resistor R13 and grounded, pin 3 is grounded, and pin 4 is connected to resistor R14; the resistor R12 is connected to the pulse detection unit; and the resistor R14 is connected to the power module.

[0028] The advantages of the present invention are:

[0029] By setting an excitation module including a self-excited oscillation unit, a bandpass filtering unit and an AC constant current source, a high-frequency AC current is applied between the excitation line and the sampling line (the contact part of the fixture) of the same polarity, and a sampling module is set to sample the excitation line and the sampling line to calculate the AC resistance of the contact part of the fixture. The reliability of the fixture contact can be quickly judged by comparing the AC resistance with a preset resistance threshold. No infrared thermal imager or high-precision ADC is required, and it is not easily affected by the complex electromagnetic environment of the industrial site. The circuit structure is simple and occupies less IO resources. Ultimately, the accuracy of the fixture contact reliability detection is greatly improved, and the detection cost is greatly reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The present invention will be further described below in conjunction with embodiments with reference to the accompanying drawings.

[0031] Figure 1 The invention discloses a circuit principle block diagram of a fixture contact reliability detection circuit for lithium battery testing.

[0032] Figure 2 1 is a circuit diagram of the excitation module of the present invention.

[0033] Figure 3 Schematic diagram of the sampling module of the present invention.

[0034] Figure 4 1 is a circuit diagram of the interface module of the present invention.

[0035] Figure 5 1 is a circuit diagram of the power module of the present invention. DETAILED DESCRIPTION

[0036] The technical solution in the embodiment of the present application has the following overall idea: an excitation module is set to apply a high-frequency AC current between an excitation line and a sampling line of the same polarity, a sampling module is set to sample the excitation line and the sampling line and then calculate the AC resistance, and the reliability of the fixture contact is judged by comparing the AC resistance with a preset resistance threshold. No infrared thermal imager or high-precision ADC is required, and it is not susceptible to electromagnetic interference. The circuit structure is simple and occupies less IO resources, so as to improve the accuracy of fixture contact reliability detection and reduce detection costs.

[0037] Please refer to Figures 1 to 5 As shown, a preferred embodiment of a fixture contact reliability detection circuit for lithium battery testing of the present invention includes an excitation module, a sampling module, an interface module and a power module;

[0038] The excitation module is used to generate an alternating current and apply it to the positive and negative terminals of the lithium battery; the sampling module is used to detect the contact resistance of the fixture and then determine the reliability of the fixture contact; the interface module is used to obtain the enable signal of the detection circuit and return the detection result; the power supply module is used to supply power to the detection circuit;

[0039] The excitation module includes a self-excited oscillation unit, a bandpass filter unit and an AC constant current source; the sampling module includes an AC small signal sampling unit, a comparison unit, a low-pass filter unit and a pulse detection unit; the interface module includes an enabling unit and an output unit;

[0040] The input end of the bandpass filter unit is connected to the output end of the self-excited oscillation unit, and the output end is connected to the input end of the AC constant current source; the input end of the comparison unit is connected to the output end of the AC small signal sampling unit, and the output end is connected to the input end of the low-pass filter unit; the input end of the pulse detection unit is connected to the output end of the low-pass filter unit, and the output end is connected to the output unit; the enabling unit is connected to the AC constant current source and the AC small signal sampling unit respectively;

[0041] The power supply module is respectively connected to the self-excited oscillation unit, the AC constant current source, the AC small signal sampling unit, the comparison unit, the low-pass filtering unit, the pulse detection unit, the enabling unit and the output unit.

[0042] The self-excited oscillation unit includes an operational amplifier U3A, a resistor R3, a resistor R4, a resistor R11, a resistor R21, a capacitor C9 and a capacitor C10; the oscillation frequency of the self-excited oscillation unit is determined by a frequency selection network composed of the resistor R3, the resistor R4, the capacitor C9 and the capacitor C10;

[0043] Pin 1 of the operational amplifier U3A is connected to capacitor C9, resistor R21 and a bandpass filter unit, pin 2 is connected to resistor R11 and resistor R21, pin 3 is connected to resistor R3, resistor R4 and capacitor C10, and pins 4 and 8 are connected to a power module; the resistor R4 is connected to capacitor C9; the resistor R3 is connected to capacitor C10 and is grounded; the resistor R11 is grounded.

[0044] The bandpass filter unit includes a resistor R6, a resistor R7, a resistor R19, a capacitor C11, a capacitor C13 and a capacitor C14; the bandpass filter unit is used to smooth the waveform of the sine wave and attenuate the signal to the linear working area of ​​the operational amplifier U3B;

[0045] One end of the resistor R6 is connected to the self-excited oscillation unit, and the other end is connected to the resistor R7 and the capacitor C13; one end of the capacitor C14 is connected to the resistor R7 and the capacitor C11, and the other end is connected to the capacitor C13 and the resistor R19 and grounded; the resistor R19 is connected to the capacitor C11 and the AC constant current source.

[0046] The AC constant current source includes an operational amplifier U2B, an operational amplifier U3B, an operational amplifier U4A, a resistor R1, a resistor R2, a resistor R5, a resistor R8, a resistor R9, a resistor R10, a resistor R20, an electrostatic protection circuit D2 and an electrostatic protection circuit D3; the operational amplifier U3B acts as a follower to input the signal of the bandpass filter unit into the AC constant current source; the sinusoidal signal is loaded to both ends of the resistor R9, according to the "virtual break" principle of the operational amplifier, the resistor R1 has almost no current flowing through it, and the resistance value of the resistor R18 is much larger than the contact resistance, so the wiring body can obtain an excitation current similar to that flowing through the resistor R9 from both ends of CT_P+ and CT_P-; CT+_1 and CT+_2 are the common terminal and normally open contact of the relay K1;

[0047] Pin 5 of the operational amplifier U3B is connected to the bandpass filter unit, and pins 6 and 7 are connected to resistor R10; pin 1 of the operational amplifier U4A is connected to resistor R8, pin 2 is connected to resistor R10 and resistor R20, pin 3 is connected to resistor R5 and resistor R2, and pins 4 and 8 are connected to the power module; pin 5 of the operational amplifier U2B is connected to resistor R1 and electrostatic protection circuit D2, and pins 6 and 7 are connected to resistor R2; one end of the resistor R9 is connected to resistor R8, electrostatic protection circuit D3 and resistor R20, and the other end is connected to resistor R1, resistor R18 and an enabling unit.

[0048] The AC small signal sampling unit includes an instrument amplifier U6, a resistor R24, a resistor R28, a resistor R33 and a capacitor C16; the AC small signal sampling unit constitutes a first-order filtering link, and its function is to obtain a differential small signal at both ends of the contact resistor when one end is not isolated from the module reference ground;

[0049] Pin 1 of the instrument amplifier U6 is connected to resistor R24 ​​and capacitor C16, pin 2 is connected to one end of resistor R28, pin 3 is connected to the other end of resistor R28, pin 4 is connected to capacitor C18 and resistor R33, pins 5 and 8 are connected to the power module, and pin 7 is connected to the comparison unit; the capacitor C16 and capacitor C18 are both connected to the enabling unit.

[0050] The comparison unit includes an operational amplifier U7A, a resistor R26, a resistor R27, a resistor R30, a capacitor C15 and a capacitor C17;

[0051] One end of the resistor R26 is connected to the AC small signal sampling unit, and the other end is connected to the resistor R27 and the capacitor C15; pins 1 and 2 of the operational amplifier U7A are connected to the resistor R30 and the capacitor C15, pin 3 is connected to the resistor R27 and the capacitor C17, and pins 4 and 8 are connected to the power module; the resistor R30 is connected to the low-pass filter unit.

[0052] The low-pass filter unit includes an operational amplifier U7B, a resistor R25, a resistor R29, a resistor R31, a resistor R34, a resistor R35, a capacitor C20 and a diode D5; the diode D5 is a voltage-stabilizing diode; the capacitor C20 is used to filter out the noise of the threshold signal generated by the power supply voltage division, and the diode D5, the resistor R29 and the resistor R31 are used to convert the positive and negative polarity pulse signals into a single polarity to match the input level requirements of the inverter U8 of the subsequent stage; when the amplitude of the output signal of the low-pass filter unit is less than the threshold voltage, CT+ is a high level; when the amplitude of the output signal of the low-pass filter unit is greater than the threshold voltage, CT+ is a low level;

[0053] Pin 5 of the operational amplifier U7B is connected to resistors R25, R34, R35 and capacitor C20, pin 6 is connected to the comparison unit, and pin 7 is connected to resistors R29, R31 and R25; the resistors R34 and R29 are both connected to the power module; the resistor R31 is connected to the output end of the diode D5 and the pulse detection unit.

[0054] The pulse detection unit includes an inverter U8, a diode D4, a resistor R32 and a capacitor C19;

[0055] Pin 1 of the inverter U8 is connected to the low-pass filter unit, pin 2 is grounded, pin 3 is connected to the output end of the resistor R32, the capacitor C19 and the diode D4, pin 4 is connected to the output unit, pin 5 is connected to the power module, and pin 6 is connected to the input end of the diode D4.

[0056] The enabling unit includes a relay K1, a diode D1, a transistor Q1, a resistor R15, a resistor R16, a resistor R17 and a capacitor C12; the relay K1 is a double-contact relay, when the enabling signal input by the resistor R17 is at a low level, the excitation module and the sampling module are disconnected through the relay K1, and the detection circuit will not affect the test process of the lithium battery;

[0057] Pin 1 of the relay K1 is connected to the input end of the diode D1 and the c-pole of the transistor Q1, pins 3 and 4 are connected to the AC small signal sampling unit, pins 5 and 6 are connected to the AC constant current source, and pin 8 is connected to the resistor R15, the capacitor C12 and the output end of the diode D1; the e-pole of the transistor Q1 is connected to the resistor R16 and grounded, and the b-pole is connected to the resistor R16 and the resistor R17; the resistor R15 is connected to the power module.

[0058] The output unit includes an optical coupler U5, a resistor R12, a resistor R13 and a resistor R14; the CT+ signal is output through the optical coupler U5, thereby isolating the detection circuit from the system-related control circuit; CT_P+ / CT_P- is a test excitation line, and CT_S+ / CT_S- is a test sampling line;

[0059] Pin 1 of the optocoupler U5 is connected to resistors R12 and R13, pin 2 is connected to resistor R13 and grounded, pin 3 is grounded, and pin 4 is connected to resistor R14; the resistor R12 is connected to the pulse detection unit; and the resistor R14 is connected to the power module.

[0060] The power module is as follows Figure 5As shown, capacitor C4 and capacitor C5 are input capacitors of the isolated DC / DC power supply U1 with positive and negative dual outputs, and capacitor C1, capacitor C2, capacitor C3, capacitor C6, capacitor C7, capacitor C8, and inductor L1 and inductor L2 form an output filter circuit.

[0061] Working principle of the present invention:

[0062] After the test fixture (test excitation line, test sampling line) is applied to the positive and negative electrode wiring bodies, an enable signal is input through the resistor R17 of the enabling unit, thereby closing the relay K1 to conduct the circuit of the excitation module and the sampling module. The excitation module generates a high-frequency sinusoidal AC current and applies it to the positive and negative electrode wiring bodies. The sampling module samples the positive and negative electrode wiring bodies in real time and calculates the AC resistance. When the test fixture is not in close contact or the surface of the positive and negative electrode wiring bodies is corroded, the AC resistance sampled by the sampling module will exceed the preset resistance threshold, thereby flipping the output level of the output unit.

[0063] In summary, the advantages of the present invention are:

[0064] By setting an excitation module including a self-excited oscillation unit, a bandpass filtering unit and an AC constant current source, a high-frequency AC current is applied between the excitation line and the sampling line (the contact part of the fixture) of the same polarity, and a sampling module is set to sample the excitation line and the sampling line to calculate the AC resistance of the contact part of the fixture. The reliability of the fixture contact can be quickly judged by comparing the AC resistance with a preset resistance threshold. No infrared thermal imager or high-precision ADC is required, and it is not easily affected by the complex electromagnetic environment of the industrial site. The circuit structure is simple and occupies less IO resources. Ultimately, the accuracy of the fixture contact reliability detection is greatly improved, and the detection cost is greatly reduced.

[0065] Although the specific implementation modes of the present invention are described above, those skilled in the art should understand that the specific implementation modes described are only illustrative and are not intended to limit the scope of the present invention. Equivalent modifications and changes made by those skilled in the art in accordance with the spirit of the present invention should be included in the scope of protection of the claims of the present invention.

Claims

1. A fixture contact reliability detection circuit for lithium battery testing, Features: It includes an excitation module, a sampling module, an interface module and a power supply module; The excitation module includes a self-excited oscillation unit, a bandpass filter unit and an AC constant current source; the sampling module includes an AC small signal sampling unit, a comparison unit, a low-pass filter unit and a pulse detection unit; the interface module includes an enabling unit and an output unit; The input end of the bandpass filter unit is connected to the output end of the self-excited oscillation unit, and the output end is connected to the input end of the AC constant current source; the input end of the comparison unit is connected to the output end of the AC small signal sampling unit, and the output end is connected to the input end of the low-pass filter unit; the input end of the pulse detection unit is connected to the output end of the low-pass filter unit, and the output end is connected to the output unit; the enabling unit is connected to the AC constant current source and the AC small signal sampling unit respectively; The power supply module is respectively connected to the self-excited oscillation unit, the AC constant current source, the AC small signal sampling unit, the comparison unit, the low-pass filtering unit, the pulse detection unit, the enabling unit and the output unit; The self-excited oscillation unit includes an operational amplifier U3A, a resistor R3, a resistor R4, a resistor R11, a resistor R21, a capacitor C9 and a capacitor C10; Pin 1 of the operational amplifier U3A is connected to capacitor C9, resistor R21 and a bandpass filter unit, pin 2 is connected to resistor R11 and resistor R21, pin 3 is connected to resistor R3, resistor R4 and capacitor C10, and pins 4 and 8 are connected to a power module; the resistor R4 is connected to capacitor C9; the resistor R3 is connected to capacitor C10 and is grounded; the resistor R11 is grounded; The bandpass filter unit includes a resistor R6, a resistor R7, a resistor R19, a capacitor C11, a capacitor C13 and a capacitor C14; One end of the resistor R6 is connected to the self-excited oscillation unit, and the other end is connected to the resistor R7 and the capacitor C13; one end of the capacitor C14 is connected to the resistor R7 and the capacitor C11, and the other end is connected to the capacitor C13 and the resistor R19 and grounded; the resistor R19 is connected to the capacitor C11 and the AC constant current source.

2. A fixture contact reliability detection circuit for lithium battery testing as claimed in claim 1, Features: The AC constant current source includes an operational amplifier U2B, an operational amplifier U3B, an operational amplifier U4A, a resistor R1, a resistor R2, a resistor R5, a resistor R8, a resistor R9, a resistor R10, a resistor R20, an electrostatic protection circuit D2 and an electrostatic protection circuit D3; Pin 5 of the operational amplifier U3B is connected to the bandpass filter unit, and pins 6 and 7 are connected to resistor R10; pin 1 of the operational amplifier U4A is connected to resistor R8, pin 2 is connected to resistor R10 and resistor R20, pin 3 is connected to resistor R5 and resistor R2, and pins 4 and 8 are connected to the power module; pin 5 of the operational amplifier U2B is connected to resistor R1 and electrostatic protection circuit D2, and pins 6 and 7 are connected to resistor R2; one end of the resistor R9 is connected to resistor R8, electrostatic protection circuit D3 and resistor R20, and the other end is connected to resistor R1, resistor R18 and an enabling unit.

3. A fixture contact reliability detection circuit for lithium battery testing as claimed in claim 1, Features: The AC small signal sampling unit includes an instrument amplifier U6, a resistor R24, a resistor R28, a resistor R33 and a capacitor C16; Pin 1 of the instrument amplifier U6 is connected to resistor R24 ​​and capacitor C16, pin 2 is connected to one end of resistor R28, pin 3 is connected to the other end of resistor R28, pin 4 is connected to capacitor C18 and resistor R33, pins 5 and 8 are connected to the power module, and pin 7 is connected to the comparison unit; the capacitor C16 and capacitor C18 are both connected to the enabling unit.

4. A fixture contact reliability detection circuit for lithium battery testing as claimed in claim 1, Features: The comparison unit includes an operational amplifier U7A, a resistor R26, a resistor R27, a resistor R30, a capacitor C15 and a capacitor C17; One end of the resistor R26 is connected to the AC small signal sampling unit, and the other end is connected to the resistor R27 and the capacitor C15; pins 1 and 2 of the operational amplifier U7A are connected to the resistor R30 and the capacitor C15, pin 3 is connected to the resistor R27 and the capacitor C17, and pins 4 and 8 are connected to the power module; the resistor R30 is connected to the low-pass filter unit.

5. A fixture contact reliability detection circuit for lithium battery testing as claimed in claim 1, Features: The low-pass filter unit includes an operational amplifier U7B, a resistor R25, a resistor R29, a resistor R31, a resistor R34, a resistor R35, a capacitor C20 and a diode D5; Pin 5 of the operational amplifier U7B is connected to resistors R25, R34, R35 and capacitor C20, pin 6 is connected to the comparison unit, and pin 7 is connected to resistors R29, R31 and R25; the resistors R34 and R29 are both connected to the power module; the resistor R31 is connected to the output end of the diode D5 and the pulse detection unit.

6. A fixture contact reliability detection circuit for lithium battery testing as claimed in claim 1, Features: The pulse detection unit includes an inverter U8, a diode D4, a resistor R32 and a capacitor C19; Pin 1 of the inverter U8 is connected to the low-pass filter unit, pin 2 is grounded, pin 3 is connected to the output end of the resistor R32, the capacitor C19 and the diode D4, pin 4 is connected to the output unit, pin 5 is connected to the power module, and pin 6 is connected to the input end of the diode D4.

7. A fixture contact reliability detection circuit for lithium battery testing as claimed in claim 1, Features: The enabling unit includes a relay K1, a diode D1, a transistor Q1, a resistor R15, a resistor R16, a resistor R17 and a capacitor C12; Pin 1 of the relay K1 is connected to the input end of the diode D1 and the c-pole of the transistor Q1, pins 3 and 4 are connected to the AC small signal sampling unit, pins 5 and 6 are connected to the AC constant current source, and pin 8 is connected to the resistor R15, the capacitor C12 and the output end of the diode D1; the e-pole of the transistor Q1 is connected to the resistor R16 and grounded, and the b-pole is connected to the resistor R16 and the resistor R17; the resistor R15 is connected to the power module.

8. A fixture contact reliability detection circuit for lithium battery testing as claimed in claim 1, Features: The output unit includes an optical coupler U5, a resistor R12, a resistor R13 and a resistor R14; Pin 1 of the optocoupler U5 is connected to resistors R12 and R13, pin 2 is connected to resistor R13 and grounded, pin 3 is grounded, and pin 4 is connected to resistor R14; the resistor R12 is connected to the pulse detection unit; and the resistor R14 is connected to the power module.

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