A current tester

Abstract

The present invention discloses a current tester, comprising a constant current source circuit, a sampling circuit, a PWM suppression and differential amplifier circuit, an analog-to-digital conversion circuit, and a microprocessor. The constant current source circuit provides a reference current for the sampling circuit. The sampling circuit inputs the sampled current signal into the PWM and differential amplifier circuits to filter out interference. The analog-to-digital conversion circuit then converts the current signal into a digital signal, which is then transmitted to the microprocessor. The present invention achieves bidirectional current detection through a rational circuit design. Furthermore, by employing the principle of current calibration, the constant current source circuit provides a reference current for the sampling circuit, effectively calibrating the sampling current, avoiding errors, and improving precision and accuracy. Compared to other similar instruments, the present invention is more compact and easier to operate.

Description

Technical Field

[0001] The present invention relates to the field of electrical technology, and in particular to a current tester. Background Art

[0002] In application scenarios such as battery charge and discharge regulators and switching power supplies, current sampling is usually used to measure current. Currently, there are various current sampling methods, each with its own advantages and disadvantages, but most of them can only achieve unidirectional current sampling. Chinese patent CN102426285A discloses a current sensor for bidirectional current sampling. The current is measured by detecting the voltage drop across a sampling resistor. The change in current flowing through the sampling resistor causes a slight change in the sampling voltage. Finally, the change is output in the form of voltage through a sampling circuit, thereby achieving bidirectional current sampling. However, the circuit lacks a current correction mechanism and cannot guarantee the accuracy and precision of sampling. Therefore, the existing technology needs to be improved. Summary of the Invention

[0003] In view of the problems existing in the prior art, the present invention provides a current tester.

[0004] To achieve the above object, the specific solutions of the present invention are as follows:

[0005] A current tester includes a constant current source circuit, a sampling circuit, a PWM suppression and differential amplifier circuit, an analog-to-digital conversion circuit, and a microprocessor. The constant current source circuit provides a reference current for the sampling circuit. The sampling circuit inputs the sampled current signal into the PWM and differential amplifier circuit to filter out interference. The analog-to-digital conversion circuit converts the current signal into a digital signal and then transmits it to the microprocessor.

[0006] Preferably, the constant current source circuit includes an amplifier U5, MOS transistors TR9 and TR4, and a resistor R6. The MOS transistor TR4 is connected to the drain of the MOS transistor TR9 as a constant current source switch, and the gate of the MOS transistor TR9 is connected to the output end of the amplifier, thereby outputting a stable voltage. The positive input end of the amplifier U5 is connected to the output end of the analog-to-digital conversion circuit, and the negative input end is grounded together with the source of the MOS transistor TR9 through the resistor R6.

[0007] Preferably, the sampling circuit includes a sampling resistor R7, and the sampling resistor R7 is connected to the input end of the PWM suppression and differential amplifier circuit.

[0008] Preferably, the PWM suppression and differential amplification circuit includes a chip U3, an output end of which is connected to an input end of the analog-to-digital conversion circuit.

[0009] Preferably, the analog-to-digital conversion circuit includes an analog-to-digital converter U2, an output end of which is connected to a positive input end of an amplifier U5.

[0010] Preferably, the microprocessor is of model STM32F401RET6, and the microprocessor is communicatively connected with the analog-to-digital conversion circuit.

[0011] Preferably, the current tester further comprises a box and a PCB board in the box, and the constant current source circuit, sampling circuit, PWM suppression and differential amplifier circuit, analog-to-digital conversion circuit, and microprocessor are all fixed on the PCB board.

[0012] The technical solution of the present invention has the following beneficial effects:

[0013] The current detection process of the present invention is a process of converting a current signal into a voltage signal. The current detection range is ±5A, and the input voltage range is 0-15V, which can meet the needs of most smart terminal devices. Bidirectional current detection is achieved through reasonable circuit design. In addition, the current calibration principle is adopted to provide a reference current for the sampling circuit through a constant current source circuit, effectively calibrating the sampling current, avoiding errors, and improving precision and accuracy. Compared with other similar instruments, it is more compact and easy to operate. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 This is an exploded view of the structure of the present invention;

[0015] Figure 2 This is a functional module block diagram of the present invention;

[0016] Figure 3 is a circuit diagram of the present invention;

[0017] Figure 4 1 is a circuit diagram of the microprocessor of the present invention.

[0018] Among them, 1-constant current source circuit, 2-sampling circuit, 3-PWM suppression and differential amplifier circuit, 4-analog-to-digital conversion circuit, 5-microprocessor, 6-computer, 7-display, 8-box cover, 9-PCB board, 10-box bottom. DETAILED DESCRIPTION

[0019] The present invention is further described below with reference to the accompanying drawings and specific embodiments.

[0020] Reference Figure 1 The present invention provides a current tester, including a box consisting of a box bottom 10 and a box cover 8 and a PCB board 9 in the box.

[0021] Reference Figure 2The PCB board 9 includes a constant current source circuit 1, a sampling circuit 2, a PWM suppression and differential amplifier circuit 3, an analog-to-digital conversion circuit 4, and a microprocessor 5. The constant current source circuit 1 provides a reference current for the sampling circuit 2. The sampling circuit 2 inputs the sampled current signal into the PWM and differential amplifier circuit 3 to filter out interference. The analog-to-digital conversion circuit 4 converts the current signal into a digital signal and then transmits it to the microprocessor 5 for corresponding processing.

[0022] Reference Figure 3 The sampling circuit 2 includes a sampling resistor R7 with a resistance of 10 mΩ, which is connected to the input end of the PWM suppression and differential amplifier circuit 3. When the measured current I passes through the sampling resistor R7, a voltage drop Uin = I × R7 is generated. Uin is input to the PWM suppression and differential amplifier circuit 3 as an input signal. When the current is 5 A, the voltage drop is only 50 mV.

[0023] The PWM suppression and differential amplifier circuit 3 includes a dedicated current sensor chip U3, which amplifies Uin by 50 times and filters the PWM noise interference and various common-mode interference therein to obtain a reference level of 2.5V, which facilitates the sampling operation of the analog-to-digital conversion circuit 4. Since the reference level of 2.5V can be positive or negative, representing positive current and negative current respectively, bidirectional detection of positive and negative currents can be achieved.

[0024] The analog-to-digital conversion circuit includes a 24-bit analog-to-digital converter U2 with a power supply voltage of 5V, a reference voltage of 2.5V, and a minimum unit of 5V / 2^24=0.298uV. Its input end is connected to the output end of U3, and the output end of U2 is connected to the constant current source circuit 1; U2 samples the voltage signal and converts it into a digital signal, and then transmits the digital signal to the microprocessor U1 through the SPI interface for further calculation.

[0025] The minimum range of current measurement corresponds to an analog-to-digital converter input voltage of 0.298uV, and the voltage drop across the 10mΩ resistor R7 is 0.298uV / 50=0.0059uV, which converts to a current of 0.0059uV / 10mΩ=0.59uA. At full scale, the ADC input voltage is ±2.5V, and the voltage drop across the 10mΩ resistor is ±2.5V / 50=±0.05V, which converts to a current of ±0.05V / 10mΩ=±5A.

[0026] Errors in circuit parameters can cause errors in the test results of the current tester. The present invention uses a constant current source circuit 1 to provide a standard current as a basis for error correction. The constant current source circuit 1 includes an amplifier U5, MOS transistors TR9 and TR4, and a resistor R6. The MOS transistor TR4 serves as a constant current source switch and is connected to the drain of the MOS transistor TR9. The gate of the MOS transistor TR9 is connected to the output of the amplifier. The positive input of the amplifier U5 is connected to the output of the analog-to-digital conversion circuit, and the negative input is connected to ground together with the source of the MOS transistor TR9 through a resistor R6. The constant current source circuit 1 uses the reference voltage of 2.5V of the analog-to-digital converter U2 as a basis and drives the 25Ω resistor R6 to obtain a standard 100mA reference current. Since the analog-to-digital converter U2 samples the same reference voltage, any errors in the reference voltage will be offset in the PWM suppression and differential amplifier circuit 3.

[0027] Reference Figure 2 and Figure 4 The microprocessor 5 adopts the model STM32F401RET6, which is connected to the analog-to-digital conversion circuit 4 to convert the digital signal into a real current value, and then sends it to the computer 6 through the USB port. Finally, the current is displayed on the display 7 of the computer 6. This part can adopt the existing technology and will not be repeated here.

[0028] The above description is only a preferred embodiment of the present invention and does not limit the patent scope of the present invention. All equivalent structural transformations made by using the contents of the present invention description and drawings under the inventive concept of the present invention, or direct / indirect application in other related technical fields are included in the protection scope of the present invention.

Claims

1. A current tester, characterized in that: It includes a constant current source circuit, a sampling circuit, a PWM suppression and differential amplifier circuit, an analog-to-digital conversion circuit, and a microprocessor. The constant current source circuit provides a reference current for the sampling circuit. The sampling circuit inputs the sampled current signal into the PWM suppression and differential amplifier circuit to filter out interference. The analog-to-digital conversion circuit converts the current signal into a digital signal and then transmits it to the microprocessor. The constant current source circuit includes an amplifier U5, a MOS transistor TR9, a MOS transistor TR4, and a resistor R6. The MOS transistor TR4 acts as a constant current source switch and is connected to the drain of the MOS transistor TR9. The gate of the MOS transistor TR9 is connected to the output of the amplifier, thereby outputting a stable voltage. The positive input of the amplifier U5 is connected to the output of the analog-to-digital conversion circuit, and the negative input is connected to the source of the MOS transistor TR9 through the resistor R6 and grounded. The sampling circuit includes a sampling resistor R7, and the sampling resistor R7 is connected to the input end of the PWM suppression and differential amplifier circuit; The PWM suppression and differential amplification circuit includes a chip U3, an output end of which is connected to an input end of an analog-to-digital conversion circuit.

2. The current tester according to claim 1, characterized in that: The analog-to-digital conversion circuit includes an analog-to-digital converter U2, an output end of which is connected to a positive input end of an amplifier U5.

3. The current tester according to claim 2, characterized in that: The microprocessor is STM32F401RET6, and the microprocessor is in communication with the analog-to-digital conversion circuit.

4. The current tester according to claim 3, characterized in that: The current tester also includes a box and a PCB board in the box. The constant current source circuit, sampling circuit, PWM suppression and differential amplifier circuit, analog-to-digital conversion circuit, and microprocessor are all fixed on the PCB board.

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