A voltage test control board

Abstract

This utility model relates to the field of voltage testing technology and discloses a voltage testing control board, including a main control circuit, an RS485 communication circuit, a TSIO open / short circuit detection circuit, a DB25 interface, a control interface, a firmware programming interface, and an LDO power supply. The LDO power supply provides the operating voltage for the entire control board. Ports TX and RX of the main control circuit are connected to the firmware programming interface and the RS485 communication circuit, respectively. Port EN of the main control circuit is connected to the RS485 communication circuit. The TISO port of the main control circuit is connected to the TSIO open / short circuit detection circuit. Ports ADD1 and ADD2 of the main control circuit are connected to the DB25 interface, and the channel interface of the DB25 interface is connected to the control interface. Interfaces A+ and B- of the DB25 interface are connected to the RS485 communication circuit, respectively. This utility model enables automatic testing of multiple voltage groups, achieves TSIO open / short circuit detection, and features low power consumption.

Description

Technical Field

[0001] This utility model relates to the field of voltage testing technology, and specifically to a voltage testing control board. Background Technology

[0002] Currently, during the production process of set-top boxes, it is necessary to test the product voltage. The product needs to be tested with 16 sets of voltages, requiring the TSIO interface to be short-circuited and low power consumption. If manual testing is required, it will involve many workstations, resulting in slow testing efficiency and making automated testing impossible. Therefore, it is necessary to develop a voltage test control board. Utility Model Content

[0003] The purpose of this invention is to address the above-mentioned problems by providing a voltage test control board that enables automatic testing of multiple voltage groups, improves testing efficiency, achieves TSIO open / short circuit detection, and consumes low power.

[0004] To achieve the above objectives, the technical solution adopted by this utility model is as follows: A voltage test control board includes a main control circuit, an RS485 communication circuit, a TSIO open / short circuit detection circuit, a DB25 interface, a control interface, a firmware burning interface, an LNB high-frequency head dummy load, a USB dummy load, and an LDO power supply. The LDO power supply is used to provide the operating voltage for the entire control board. The output terminal of the LDO power supply is connected to the power supply terminals of the main control circuit and the RS485 communication circuit, respectively. The input terminal of the LDO power supply is connected to the power supply terminals of the TSIO open / short circuit detection circuit and the DB25 interface, respectively. The transmitting port TX and receiving port RX of the main control circuit are... The main control circuit is connected to the firmware burning interface and the RS485 communication circuit. The enable port EN of the main control circuit is connected to the RS485 communication circuit. The TISO detection port of the main control circuit is connected to the TSIO open / short circuit detection circuit. The ADD1 port and ADD2 port of the main control circuit are respectively connected to the DB25 interface. The control interface is a 16-channel interface. The channel interfaces of the DB25 interface are connected to the control interface. Two of the channel interfaces are also connected to the LNB high-frequency head dummy load and the USB dummy load, respectively. The serial communication interfaces A+ and B- of the DB25 interface are respectively connected to the RS485 communication circuit.

[0005] Furthermore, the LDO power supply consists of a low-dropout linear regulator U3, resistors R20 and R21. The input terminal of the low-dropout linear regulator U3 is connected to the AF12V input power supply terminal through parallel resistors R20 and R21, and its output terminal is a 3V3 power supply terminal. The AF12V input power supply terminal is connected to the TSIO open / short circuit and the DB25 interface, respectively. The 3V3 power supply terminal is connected to the main control circuit, the RS485 communication circuit, and the TSIO open / short circuit.

[0006] Furthermore, the main control circuit includes a microcontroller U4, a voltage filter circuit, an LED indicator circuit, and an electronic switch circuit. The microcontroller U4 is model STC8G1K08 QFN20. The VCC power supply terminal of the microcontroller U4 is grounded through capacitor C7 and connected to a 3V3 power supply terminal. The voltage filter circuit consists of resistors R23 and R22 and capacitor C9, used for input filtering of the detected voltage to improve the circuit's anti-interference capability. The P3.2 terminal of the microcontroller U4 is grounded through parallel resistors R22 and C9, and the P3.2 terminal of the microcontroller U4 is connected to a 3.3V solder joint through resistor R23. The LED indicator circuit consists of resistor R24, capacitor C10, and an LED solder joint. The circuit consists of a point used to indicate serial port data transmission and reception. The P1.5 terminal of the microcontroller U4 is grounded through capacitor C10, and the P1.5 terminal of the microcontroller U4 is connected to the LED solder joint through resistor R24. The electronic switch circuit consists of resistor R17 and transistor Q1, used to trigger the product to enter the low-power mode. The base of transistor Q1 is connected to the P5.4 terminal of the microcontroller U4 through resistor R17, the emitter of transistor Q1 is grounded, and the collector of transistor Q1 is connected to the SYS solder joint.

[0007] Furthermore, the DB25 interface includes a chip DB25, resistors R25 and R26. Pin 3 of the chip DB25 is connected to the ADD1 port of the microcontroller U4 through resistor R26. Pin 16 of the chip DB25 is connected to the ADD2 port of the microcontroller U4 through resistor R25. Pin 1 of the chip DB25 is connected to a 12V solder joint. The 16 channels of the chip DB25 are respectively connected to the 16 channels of the control interface. Among them, channels CH9 and CH3 are also connected to the LNB high-frequency head dummy load and the USB dummy load, respectively. Pins 4, 5, 26, and 27 of the chip DB25 are all grounded.

[0008] Furthermore, the RS485 communication circuit includes an interface module U2, resistors R1, R7, R8 and R9. The interface module U2 includes a power supply pin VCC, a ground pin GND, an enable pin RE, an enable pin DE, a data transmission pin RO, a data transmission pin DI, an input / output pin A and an input / output pin B.

[0009] The power supply pin VCC is grounded through capacitor C2, and the power supply pin VCC is connected to the 3V3 power supply terminal. The grounding pin GND is grounded.

[0010] The enable pin RE and the enable pin DE are connected to the enable port EN of the microcontroller U4. The enable pin RE and the enable pin DE are connected to ground through resistor R1.

[0011] The data transmission pin RO is connected to the receiving port RX of the microcontroller U4 through the resistor R7, and the data transmission pin DI is connected to the transmitting port TX of the microcontroller U4 through the resistor R8;

[0012] The input / output pin A is connected to a 3V3 power supply terminal through resistor R10, and the input / output pin B is grounded through resistor R9. The input / output pin A is connected to the serial communication interface A+ of the DB25 interface, and the input / output pin B is connected to the serial communication interface B- of the DB25 interface.

[0013] Furthermore, the TSIO open / short circuit includes an isolation power supply M1, a surface-mount optocoupler OP1, a transistor Q2, a voltage comparator U5A, a voltage comparator U5B, and a diode D1;

[0014] The VIN terminal of the isolation power supply M1 is connected to the AF12V input power supply terminal, the VOUT terminal of the isolation power supply M1 is connected to the analog ground AGND through capacitor C15, the OGND terminal of the isolation power supply M1 is connected to the analog ground AGND, and the VGND terminal of the isolation power supply M1 is grounded.

[0015] The anode of the surface mount optocoupler OP1 is connected to the VOUT terminal of the isolation power supply M1 through resistor R12, and its cathode is connected to the collector of the transistor Q2; the collector of the surface mount optocoupler OP1 is connected to the 3V3 power supply terminal through resistor R13, and the collector of the surface mount optocoupler OP1 is also connected to the TISO detection port of the microcontroller U4; the emitter of the surface mount optocoupler OP1 is grounded.

[0016] The base of transistor Q2 is connected to the simulated ground line AGND via resistor R39, and the emitter of transistor Q2 is connected to the simulated ground line AGND.

[0017] The positive input terminal of the voltage comparator U5B is connected to the power supply terminal A5V through resistors R33 and R30. The other end of resistor R30 is connected to one end of solder joint TP16, and the other end of solder joint TP18 is connected to the analog ground AGND. The negative input terminal of the voltage comparator U5B is connected to one end of resistors R31 and R32 respectively. The other end of resistor R31 is connected to the A5V power supply terminal, and the other end of resistor R32 is connected to the analog ground AGND. The output terminal of the voltage comparator U5B is connected to the base of transistor Q2 through resistors R37 and R29. The connection between resistors R37 and R29 is connected to the output terminal of voltage comparator U5A through diode D1. The positive power supply terminal of the voltage comparator U5B is connected to the A5V power supply terminal, and the negative power supply terminal of the voltage comparator U5B is connected to the analog ground AGND.

[0018] The positive input terminal of the voltage comparator U5A is connected to resistors R34 and R35 respectively. The other end of resistor R34 is connected to the analog ground AGND, and the other end of resistor R35 is connected to the A5V power supply terminal. The negative input terminal of the voltage comparator U5A is connected to the junction of resistors R30 and R33 through resistor R36.

[0019] By adopting the above technical solution, this utility model has the following beneficial effects:

[0020] This utility model can test 16 groups of voltages for products, realize multi-channel control to improve production efficiency, and achieve linkage and error prevention after networking.

[0021] This utility model's board MCU receives commands and controls the board under test to enter different states, realizing TSIO open / short circuit detection, RS485 networking control, and low power consumption. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the module connection structure of a voltage test control board according to the present invention;

[0023] Figure 2 This is a circuit diagram of the main control circuit of this utility model;

[0024] Figure 3 The circuit diagram shows the firmware burning interface, DB25 interface, and control interface of this utility model.

[0025] Figure 4 This is a circuit diagram of the RS485 communication circuit of this utility model;

[0026] Figure 5 This is a circuit diagram of the TSIO open / short circuit detection circuit of this utility model;

[0027] Figure 6 The circuit diagrams for the LNB high-frequency head dummy load and USB dummy load of this utility model are shown below.

[0028] Figure 7 This is the circuit diagram of the LDO power supply of this utility model;

[0029] In the diagram: 1-Main control circuit, 2-Firmware burning interface, 3-LDO power supply, 4-RS485 communication circuit, 5-TSIO open / short circuit detection circuit, 6-DB25 interface, 7-Control interface, 8-LNB high-frequency head dummy load, 9-USB dummy load. Detailed Implementation

[0030] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the present invention pertains. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the present invention. The terms "first," "second," etc., in the specification, claims, and accompanying drawings of the present invention are used to distinguish different objects and not to describe a particular order. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or device that includes a series of steps or units is not limited to the listed steps or units, but may optionally include steps or units not listed, or may optionally include other steps or units inherent to these processes, methods, products, or devices.

[0031] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of the present invention. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0032] like Figure 1As shown in the figure, a voltage test control board includes a main control circuit 1, an RS485 communication circuit 4, a TSIO open / short circuit detection circuit 5, a DB25 interface 6, a control interface 7, a firmware burning interface 2, an LNB high-frequency head dummy load 8, a USB dummy load 9, and an LDO power supply 3. The LDO power supply 3 provides the operating voltage for the entire control board. The output terminal of the LDO power supply 3 is connected to the power supply terminals of the main control circuit 1 and the RS485 communication circuit 4, respectively. The input terminal of the LDO power supply 3 is connected to the power supply terminals of the TSIO open / short circuit detection circuit 5 and the DB25 interface 6, respectively. The transmitting port TX and receiving port RX of the main control circuit 1 are respectively connected to the firmware burning interface 6. The main control circuit 1 is connected to the RS485 communication circuit 4 via port 2. The enable port EN of the main control circuit 1 is connected to the RS485 communication circuit 4. The TISO detection port of the main control circuit 1 is connected to the TSIO open / short circuit detection circuit 5. The ADD1 port and ADD2 port of the main control circuit 1 are respectively connected to the DB25 interface 6. The control interface 7 is a 16-channel interface. The channel interfaces of the DB25 interface 6 are connected to the control interface 7. Two of the channel interfaces are also connected to the LNB high-frequency head dummy load 8 and the USB dummy load 9, respectively. The serial communication interfaces A+ and B- of the DB25 interface 6 are respectively connected to the RS485 communication circuit 4.

[0033] LDO power supply 3 provides operating voltage for the entire control board. The USB and high-frequency head dummy loads provide load to bring the product's USB and high-frequency head into a loaded state. RS485 communication circuit 4 is used for multi-channel network communication. Firmware programming interface 2 and control interface 7 are used for programming microcontroller firmware and controlling the product to enter different states. TSIO open / short circuit 5 detects the product's open / short circuit status. DB25 interface 6 is used for communication with a computer.

[0034] like Figure 7 As shown in the figure, the LDO power supply 3 consists of a low-dropout linear regulator U3, resistors R20 and R21. The input terminal of the low-dropout linear regulator U3 is connected to the AF12V input power supply terminal through the parallel resistors R20 and R21. Its output terminal is a 3V3 power supply terminal. The AF12V input power supply terminal is connected to the TSIO open / short circuit detection circuit 5 and the DB25 interface 6, respectively. The 3V3 power supply terminal is connected to the main control circuit 1, the RS485 communication circuit 4, and the TSIO open / short circuit detection circuit 5, respectively. In the LDO power supply 33, the input voltage of the AF12V terminal is 12V, and the output voltage of the 3V3 terminal is 3.3V.

[0035] like Figure 2As shown in the figure, the main control circuit 1 includes a microcontroller U4, a voltage filter circuit, an LED indicator circuit, and an electronic switch circuit. The microcontroller U4 is model STC8G1K08 QFN20. The VCC power supply terminal of the microcontroller U4 is grounded through capacitor C7 and connected to a 3V3 power supply terminal. The voltage filter circuit consists of resistors R23 and R22 and capacitor C9, used for input filtering of the detected voltage to improve the circuit's anti-interference capability. The P3.2 terminal of the microcontroller U4 is grounded through parallel resistors R22 and C9, and the P3.2 terminal of the microcontroller U4 is connected to a 3.3V solder joint through resistor R23. The LED indicator circuit consists of resistor R24, capacitor C10, and an LED solder joint. The circuit consists of a dotted line to indicate serial port data transmission and reception. The P1.5 terminal of the microcontroller U4 is grounded through capacitor C10, and the P1.5 terminal of the microcontroller U4 is connected to the LED solder joint through resistor R24. The electronic switch circuit consists of resistor R17 and transistor Q1, used to trigger the product to enter low-power mode. The base of transistor Q1 is connected to the P5.4 terminal of the microcontroller U4 through resistor R17, the emitter of transistor Q1 is grounded, and the collector of transistor Q1 is connected to the SYS solder joint. The transistor Q1 is an MMBT5551 G1.

[0036] like Figure 3 As shown in the figure, the DB25 interface 6 includes a chip DB25, resistors R25 and R26. Pin 3 of the chip DB25 is connected to the ADD1 port of the microcontroller U4 through resistor R26. Pin 16 of the chip DB25 is connected to the ADD2 port of the microcontroller U4 through resistor R25. Pin 1 of the chip DB25 is connected to a 12V solder joint. The 16 channels of the chip DB25 are respectively connected to the 16 channels of the control interface 7. Among them, channels CH9 and CH3 are also connected to the LNB high-frequency head dummy load 8 and USB dummy load 9, respectively. Pins 4, 5, 26, and 27 of the chip DB25 are all grounded.

[0037] like Figure 4 As shown in the figure, the RS485 communication circuit 4 includes an interface module U2, resistors R1, R7, R8 and R9. The interface module U2 includes a power supply pin VCC, a ground pin GND, an enable pin RE, an enable pin DE, a data transmission pin RO, a data transmission pin DI, an input / output pin A and an input / output pin B.

[0038] The power supply pin VCC is grounded through capacitor C2, and the power supply pin VCC is connected to the 3V3 power supply terminal. The grounding pin GND is grounded.

[0039] The enable pin RE and the enable pin DE are connected to the enable port EN of the microcontroller U4. The enable pin RE and the enable pin DE are connected to ground through resistor R1.

[0040] The data transmission pin RO is connected to the receiving port RX of the microcontroller U4 through the resistor R7, and the data transmission pin DI is connected to the transmitting port TX of the microcontroller U4 through the resistor R8;

[0041] The input / output pin A is connected to a 3V3 power supply terminal through resistor R10, and the input / output pin B is grounded through resistor R9. The input / output pin A is connected to the serial communication interface A+ of the DB25 interface 6, and the input / output pin B is connected to the serial communication interface B- of the DB25 interface 6.

[0042] The TSIO open / short circuit 5 includes an isolation power supply M1, a surface mount optocoupler OP1, a transistor Q2, a voltage comparator U5A, a voltage comparator U5B, and a diode D1. The isolation power supply M1 is model B1205S-1WR3, the surface mount optocoupler OP1 is model EL357N(B)(TA)-G, the transistor Q2 is model MMBT5551 G1, the diode D1 is model LL4148, and the voltage comparators U5A and U5B are both model LM358.

[0043] The VIN terminal of the isolation power supply M1 is connected to the AF12V input power supply terminal, the VOUT terminal of the isolation power supply M1 is connected to the analog ground AGND through capacitor C15, the OGND terminal of the isolation power supply M1 is connected to the analog ground AGND, and the VGND terminal of the isolation power supply M1 is grounded.

[0044] The anode of the surface mount optocoupler OP1 is connected to the VOUT terminal of the isolation power supply M1 through resistor R12, and its cathode is connected to the collector of the transistor Q2; the collector of the surface mount optocoupler OP1 is connected to the 3V3 power supply terminal through resistor R13, and the collector of the surface mount optocoupler OP1 is also connected to the TISO detection port of the microcontroller U4; the emitter of the surface mount optocoupler OP1 is grounded.

[0045] The base of transistor Q2 is connected to the simulated ground line AGND via resistor R39, and the emitter of transistor Q2 is connected to the simulated ground line AGND.

[0046] The positive input terminal of the voltage comparator U5B is connected to the power supply terminal A5V through resistors R33 and R30. The other end of resistor R30 is connected to one end of solder joint TP16, and the other end of solder joint TP18 is connected to the analog ground AGND. The negative input terminal of the voltage comparator U5B is connected to one end of resistors R31 and R32 respectively. The other end of resistor R31 is connected to the A5V power supply terminal, and the other end of resistor R32 is connected to the analog ground AGND. The output terminal of the voltage comparator U5B is connected to the base of transistor Q2 through resistors R37 and R29. The connection between resistors R37 and R29 is connected to the output terminal of voltage comparator U5A through diode D1. The positive power supply terminal of the voltage comparator U5B is connected to the A5V power supply terminal, and the negative power supply terminal of the voltage comparator U5B is connected to the analog ground AGND.

[0047] The positive input terminal of the voltage comparator U5A is connected to resistors R34 and R35 respectively. The other end of resistor R34 is connected to the analog ground AGND, and the other end of resistor R35 is connected to the A5V power supply terminal. The negative input terminal of the voltage comparator U5A is connected to the junction of resistors R30 and R33 through resistor R36.

[0048] To prevent external interference, the isolation power supply M1 uses an operational amplifier to form a voltage comparator to continuously detect the resistance on the TSIO interface of the product connected between TP16 and TP18. When there is a short circuit or open circuit, it outputs a low level; otherwise, it outputs a high level.

[0049] The present invention has been described in detail above. However, modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, any modifications or improvements that do not depart from the spirit of the present invention are within the protection scope of the present invention.

Claims

1. A voltage test control board, characterized in that, The system includes a main control circuit, an RS485 communication circuit, a TSIO open / short circuit detection circuit, a DB25 interface, a control interface, a firmware programming interface, an LNB high-frequency head dummy load, a USB dummy load, and an LDO power supply. The LDO power supply provides the operating voltage for the entire control board. The output of the LDO power supply is connected to the power supply terminals of the main control circuit and the RS485 communication circuit, respectively. The input of the LDO power supply is connected to the power supply terminals of the TSIO open / short circuit detection circuit and the DB25 interface, respectively. The transmit port TX and receive port RX of the main control circuit are connected to the firmware programming interface and the RS485 interface, respectively. The communication circuit is connected as follows: the enable port EN of the main control circuit is connected to the RS485 communication circuit; the TISO detection port of the main control circuit is connected to the TSIO open / short circuit detection circuit; the ADD1 and ADD2 ports of the main control circuit are respectively connected to the DB25 interface; the control interface is a 16-channel interface; the channel interfaces of the DB25 interface are connected to the control interface; two of the channel interfaces are also respectively connected to the LNB high-frequency head dummy load and the USB dummy load; and the serial communication interfaces A+ and B- of the DB25 interface are respectively connected to the RS485 communication circuit.

2. The voltage test control board according to claim 1, characterized in that, The LDO power supply consists of a low-dropout linear regulator U3, resistors R20 and R21. The input terminal of the low-dropout linear regulator U3 is connected to the AF12V input power supply terminal through parallel resistors R20 and R21. Its output terminal is a 3V3 power supply terminal. The AF12V input power supply terminal is connected to the TSIO open / short circuit and the DB25 interface, respectively. The 3V3 power supply terminal is connected to the main control circuit, the RS485 communication circuit, and the TSIO open / short circuit.

3. A voltage test control board according to claim 1, characterized in that, The main control circuit includes a microcontroller U4, a voltage filter circuit, an LED indicator circuit, and an electronic switch circuit. The microcontroller U4 is model STC8G1K08 QFN20. The VCC power supply terminal of the microcontroller U4 is grounded through capacitor C7 and connected to a 3V3 power supply terminal. The voltage filter circuit, composed of resistors R23 and R22 and capacitor C9, is used for input voltage filtering to improve the circuit's anti-interference capability. The P3.2 terminal of the microcontroller U4 is grounded through parallel connections of R22 and resistor C9. The P3.2 terminal of the microcontroller U4 is connected to a 3.3V solder joint through resistor R23. The LED indicator circuit consists of resistor R24, capacitor C10, and an LED solder joint. The circuit consists of a point used to indicate serial port data transmission and reception. The P1.5 terminal of the microcontroller U4 is grounded through capacitor C10, and the P1.5 terminal of the microcontroller U4 is connected to the LED solder joint through resistor R24. The electronic switch circuit consists of resistor R17 and transistor Q1, used to trigger the product to enter the low-power mode. The base of transistor Q1 is connected to the P5.4 terminal of the microcontroller U4 through resistor R17, the emitter of transistor Q1 is grounded, and the collector of transistor Q1 is connected to the SYS solder joint.

4. A voltage test control board according to claim 3, characterized in that, The DB25 interface includes a chip DB25, resistors R25 and R26. Pin 3 of the chip DB25 is connected to the ADD1 port of the microcontroller U4 through resistor R26. Pin 16 of the chip DB25 is connected to the ADD2 port of the microcontroller U4 through resistor R25. Pin 1 of the chip DB25 is connected to a 12V solder joint. The 16 pins of the chip DB25 are respectively connected to the 16 pins of the control interface. Among them, pins CH9 and CH3 are also connected to the LNB high-frequency head dummy load and the USB dummy load, respectively. Pins 4, 5, 26, and 27 of the chip DB25 are all grounded.

5. A voltage test control board according to claim 3, characterized in that, The RS485 communication circuit includes an interface module U2, resistors R1, R7, R8, and R9. The interface module U2 includes a power supply pin VCC, a ground pin GND, an enable pin RE, an enable pin DE, a data transmission pin RO, a data transmission pin DI, an input / output pin A, and an input / output pin B. The power supply pin VCC is grounded through capacitor C2, and the power supply pin VCC is connected to the 3V3 power supply terminal. The grounding pin GND is grounded. The enable pin RE and the enable pin DE are connected to the enable port EN of the microcontroller U4. The enable pin RE and the enable pin DE are connected to ground through resistor R1. The data transmission pin RO is connected to the receiving port RX of the microcontroller U4 through the resistor R7, and the data transmission pin DI is connected to the transmitting port TX of the microcontroller U4 through the resistor R8; The input / output pin A is connected to a 3V3 power supply terminal through resistor R10, and the input / output pin B is grounded through resistor R9. The input / output pin A is connected to the serial communication interface A+ of the DB25 interface, and the input / output pin B is connected to the serial communication interface B- of the DB25 interface.

6. A voltage test control board according to claim 3, characterized in that, The TSIO open / short circuit includes an isolation power supply M1, a surface mount optocoupler OP1, a transistor Q2, a voltage comparator U5A, a voltage comparator U5B, and a diode D1. The VIN terminal of the isolation power supply M1 is connected to the AF12V input power supply terminal, the VOUT terminal of the isolation power supply M1 is connected to the analog ground AGND through capacitor C15, the OGND terminal of the isolation power supply M1 is connected to the analog ground AGND, and the VGND terminal of the isolation power supply M1 is grounded. The anode of the surface mount optocoupler OP1 is connected to the VOUT terminal of the isolation power supply M1 through resistor R12, and its cathode is connected to the collector of the transistor Q2; the collector of the surface mount optocoupler OP1 is connected to the 3V3 power supply terminal through resistor R13, and the collector of the surface mount optocoupler OP1 is also connected to the TISO detection port of the microcontroller U4; the emitter of the surface mount optocoupler OP1 is grounded. The base of transistor Q2 is connected to the simulated ground line AGND via resistor R39, and the emitter of transistor Q2 is connected to the simulated ground line AGND. The positive input terminal of the voltage comparator U5B is connected to the power supply terminal A5V through resistors R33 and R30. The other end of resistor R30 is connected to one end of solder joint TP16, and the other end of solder joint TP18 is connected to the analog ground AGND. The negative input terminal of the voltage comparator U5B is connected to one end of resistors R31 and R32 respectively. The other end of resistor R31 is connected to the A5V power supply terminal, and the other end of resistor R32 is connected to the analog ground AGND. The output terminal of the voltage comparator U5B is connected to the base of transistor Q2 through resistors R37 and R29. The connection between resistors R37 and R29 is connected to the output terminal of voltage comparator U5A through diode D1. The positive power supply terminal of the voltage comparator U5B is connected to the A5V power supply terminal, and the negative power supply terminal of the voltage comparator U5B is connected to the analog ground AGND. The positive input terminal of the voltage comparator U5A is connected to resistors R34 and R35 respectively. The other end of resistor R34 is connected to the analog ground AGND, and the other end of resistor R35 is connected to the A5V power supply terminal. The negative input terminal of the voltage comparator U5A is connected to the junction of resistors R30 and R33 through resistor R36.

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