Constant current source module for resistance measurement

Abstract

The utility model relates to a constant current source module, in particular to a constant current source module for resistance measurement, which comprises a current stabilization unit and a switching unit, the current stabilization unit comprises a constant voltage source, a protection circuit and a feedback circuit, and the switching unit comprises a current switching circuit and a relay control circuit. The constant voltage source and the relay control circuit are connected with the current switching circuit, the current switching circuit is connected with the protection circuit and the feedback circuit, and the feedback circuit is connected with the constant voltage source. According to the utility model, the relay is controlled by the external controller through I2C communication to carry out current gear switching, the test is stable and accurate, an analog circuit and a digital circuit are separated, the system works stably, multi-channel automatic switching is realized, the operation is simple, the defects of the prior art are overcome, and the design of low cost, low volume, miniaturization, light weight and modularization is realized.

Description

Technical Field

[0001] The utility model relates to a constant current source module, specifically to a constant current source module for resistance measurement. Background Art

[0002] A constant current source is a wide-spectrum, high-precision AC constant current power supply, which has the advantages of fast response speed, high constant current accuracy, long-term stable operation, and suitability for various types of loads. It is mainly used in production occasions such as detecting thermal relays, molded case circuit breakers, miniature circuit breakers, and where it is necessary to set rated current, operating current, short-circuit protection current, etc.

[0003] Resistance measurement is one of the basic experiments in multiple fields such as electronic engineering, materials science, and physics. Accurately measuring the resistance value is of great significance for understanding material properties, evaluating the performance of electronic components, and fault diagnosis. In resistance measurement, a constant current source module can provide a stable current source, thereby eliminating measurement errors caused by current changes and improving measurement accuracy.

[0004] However, in the design and manufacturing process of existing constant current sources, in order to ensure their high precision and stability, high-quality components and complex circuit structures need to be used, which will increase the manufacturing cost and make the price of the constant current source relatively high. Since the constant current source contains multiple electronic components and complex circuits, its volume and weight are relatively large. This to a certain extent limits the application of the constant current source in equipment that requires miniaturization or lightweight.

[0005] In order to solve the above problems of high cost, large volume and weight, a constant current source module for resistance measurement is proposed. Summary of the Utility Model

[0006] The purpose of the utility model is to provide a constant current source module for resistance measurement to solve the problems raised in the above background art.

[0007] To achieve the above purpose, the utility model provides a constant current source module for resistance measurement, including a constant current unit and a switching unit. The constant current unit includes a constant voltage source, a protection circuit and a feedback circuit. The switching unit includes a current switching circuit and a relay control circuit. The constant voltage source and the relay control circuit are both connected to the current switching circuit. The current switching circuit is connected to the protection circuit and the feedback circuit. The feedback circuit is connected to the constant voltage source;

[0008] The constant voltage source provides current for the current switching circuit. The external controller controls the current switching circuit to switch the output current through the relay control circuit, and the feedback circuit collects the current and feeds it back to the constant voltage source to ensure the stability of the current output.

[0009] As a further improvement of this technical solution, the constant voltage source includes chips U303 and U304, where,

[0010] The REF terminal of chip U303 is connected to the AMP_REF terminal;

[0011] The negative terminal of chip U303 is connected to capacitor C310 and grounded;

[0012] The V- terminal of chip U303 is connected to the PN12V terminal and the other end of capacitor C310;

[0013] The SENSE terminal of chip U303 is connected to the OUT terminal of chip U303 and the AMP_OUT terminal;

[0014] The V+ terminal of chip U303 is connected to capacitor C307 and the PP12V terminal, and capacitor C307 is grounded;

[0015] The positive terminal of chip U303 is connected to the OUT terminal of chip U304 and capacitor C309;

[0016] The IN terminal of chip U304 is connected to resistor R323, resistor R323 is connected to capacitor C306 and the PP5V terminal, and capacitor C306 is grounded;

[0017] The GND terminal of chip U304 is connected to the other end of capacitor C309 and grounded.

[0018] As a further improvement of this technical solution, the relay control circuit includes chips J501, U401, U402, and U403, where,

[0019] The A2 terminal of chip U401 is connected to resistor R401, the A1 terminal of chip U401 is connected to resistor R402, the A0 terminal of chip U401 is connected to resistor R403, the RESET terminal of chip U401 is connected to resistor R404, resistor R404 is connected to the PP5V terminal, and resistors R401, R402, and R403 are all grounded;

[0020] The VSS terminal of chip U401 is grounded, the VDD terminal of chip U401 is connected to capacitor C401 and the PP5V terminal, capacitor C401 is grounded, the SCK terminal of chip U401 is connected to the SCL2 terminal of chip U403 and resistor R408, the SI terminal of chip U401 is connected to the SDA2 terminal of chip U403 and resistor R407, and resistor R407 is connected to the other end of resistor R408 and the PP5V terminal;

[0021] The GP0 terminal of the chip U401 is connected to the I1 terminal of the chip U402, the GP1 terminal of the chip U401 is connected to the I2 terminal of the chip U402, the GP2 terminal of the chip U401 is connected to the I3 terminal of the chip U402, the GP3 terminal of the chip U401 is connected to the I4 terminal of the chip U402, the GP4 terminal of the chip U401 is connected to the I5 terminal of the chip U402, the GP5 terminal of the chip U401 is connected to the I6 terminal of the chip U402, and the GP6 terminal of the chip U401 is connected to the I7 terminal of the chip U402;

[0022] The VDD1 terminal of the chip U403 is connected to the capacitor C403 and to the I2C_PWR terminal, the capacitor C403 is grounded, the GND1 and GND2 terminals of the chip U403 are grounded, the VDD2 terminal of the chip U403 is connected to the capacitor C404 and to the PP5V terminal, and the capacitor C404 is grounded;

[0023] The SDA1 terminal of the chip U403 is connected to the 12th pin of the chip J501 and to the dual Schottky diode D502, and the SCL1 terminal of the chip U403 is connected to the 10th pin of the chip J501 and to the dual Schottky diode D501.

[0024] As a further improvement of this technical solution, the current switching circuit includes a six-way relay circuit, the constant voltage source is connected to the relay circuit, and the relay circuit is connected to the feedback circuit and the protection circuit.

[0025] As a further improvement of this technical solution, the feedback circuit includes the chip U305,

[0026] The negative terminal and the OUT terminal of the chip U305 are connected to the REF terminal of the chip U303;

[0027] The positive terminal of the chip U305 is connected to the resistor R324 and to the relay circuit, and the resistor R324 is connected to the capacitor C308 and grounded;

[0028] The V- terminal of the chip U305 is connected to the capacitor C311 and to the PN12V terminal, and the capacitor C311 is grounded;

[0029] The V+ terminal of the chip U305 is connected to the other end of the capacitor C308 and to the PP12V terminal.

[0030] As a further improvement of this technical solution, the protection circuit includes the relay K303 and the chip U302,

[0031] Pin 1 of the relay K303 is connected to the resistor R307 and also to the PP5V terminal. The resistor R307 is connected to the light-emitting diode D302. The light-emitting diode D302 is connected to pin 8 of the relay K303 and also to the O7 terminal of the chip U402.

[0032] Pin 3 of the relay K303 is connected to the positive electrode of the diode D304 and also to the IN- terminal of the chip U302. The diode D304 is connected to the VOUT terminal of the chip U302.

[0033] Pin 4 of the relay K303 is connected to the relay circuit.

[0034] The V- terminal of the chip U302 is connected to the capacitor C303 and also to the PN12V terminal. The capacitor C303 is grounded.

[0035] The IN+ terminal of the chip U302 is connected to the resistors R314 and R315. The resistor R314 is connected to the capacitor C304 and also to the PN12V terminal. The capacitor C304 is grounded. The resistor R315 is connected to the capacitor C305 and also to the PN12V terminal. The capacitor C305 is grounded.

[0036] The V+ terminal of the chip U302 is connected to the capacitor C302 and also to the PP12V terminal. The capacitor C302 is grounded.

[0037] Compared with the prior art, the beneficial effects of the present utility model are as follows:

[0038] In this constant current source module for resistance measurement, the external controller controls the relay through I2C communication for current gear switching. The test is stable and accurate. The analog circuit and the digital circuit are separated, the system works stably, and it has multi-channel automatic switching, simple operation, overcomes the shortcomings of the prior art, and realizes low-cost, low-volume, miniaturized, lightweight, and modular design. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 is the overall structure diagram of the present utility model;

[0040] Figure 2 is the constant voltage source circuit diagram of the present utility model;

[0041] Figure 3 is the relay control circuit of the present utility model Figure 1 ;

[0042] Figure 4 is the relay control circuit of the present utility model Figure 2 ;

[0043] Figure 5 is the relay control circuit of the present utility model Figure 3 ;

[0044] Figure 6 is the relay control circuit of the present utility model Figure 4 ;

[0045] Figure 7 is the current switching circuit of the present utility model Figure 1 ;

[0046] Figure 8 is the current switching circuit of the present utility model Figure 2 ;

[0047] Figure 9 is the current switching circuit of the present utility model Figure 3 ;

[0048] Figure 10 is the feedback circuit diagram of the present utility model;

[0049] Figure 11 is the protection circuit diagram of the present utility model. Specific embodiments

[0050] Next, the technical solutions in the embodiments of the present utility model will be clearly and completely described in conjunction with the accompanying drawings in the present utility model. Obviously, the described embodiments are only a part of the embodiments of the present utility model, rather than all the embodiments. Based on the embodiments in the present utility model, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present utility model.

[0051] Basic principle of the constant current source: The constant current source is a power source that can output a stable and constant current. Its output current will not change due to the change of the circuit load. This characteristic makes the constant current source particularly important in application scenarios where precise current control is required.

[0052] The working principle of the constant current source is usually based on negative feedback control. By comparing the actual output current with the set current, the input voltage or circuit parameters are adjusted to ensure the constancy of the output current.

[0053] Please refer to Figures 1-11 As shown, this embodiment provides a constant current source module for resistance measurement, including a current stabilizing unit and a switching unit. The current stabilizing unit includes a constant voltage source, a protection circuit, and a feedback circuit. The switching unit includes a current switching circuit and a relay control circuit. The constant voltage source and the relay control circuit are both connected to the current switching circuit. The current switching circuit is connected to the protection circuit and the feedback circuit. The feedback circuit is connected to the constant voltage source;

[0054] The constant voltage source provides current for the current switching circuit. The external controller controls the current switching circuit to switch the output current through the relay control circuit, and the feedback circuit collects the current and feeds it back to the constant voltage source to ensure the stability of the current output.

[0055] The constant voltage source includes chips U303 and U304. Among them,

[0056] The REF terminal of chip U303 is connected to the AMP_REF terminal;

[0057] The negative terminal of chip U303 is connected to capacitor C310 and grounded;

[0058] The V- terminal of chip U303 is connected to the PN12V terminal and the other end of capacitor C310;

[0059] The SENSE terminal of chip U303 is connected to the OUT terminal of chip U303 and the AMP_OUT terminal;

[0060] The V+ terminal of chip U303 is connected to capacitor C307 and the PP12V terminal, and capacitor C307 is grounded;

[0061] The positive terminal of chip U303 is connected to the OUT terminal of chip U304 and capacitor C309;

[0062] The IN terminal of chip U304 is connected to resistor R323. Resistor R323 is connected to capacitor C306 and the PP5V terminal, and capacitor C306 is grounded;

[0063] The GND terminal of chip U304 is connected to the other end of capacitor C309 and grounded.

[0064] Chip U303 is an operational amplifier. In this embodiment, the INA105KU / 2K5 type is preferably adopted. Chip U304 is a voltage reference chip. In this embodiment, the REF3025AIDBZR type is preferably adopted. In the constant voltage source, chip U304 provides 2.5V voltage to chip U303. The operational amplifier chip U303 outputs a stable 2.5V voltage and can adjust the output voltage in real time according to the subsequent circuit.

[0065] The relay control circuit includes chips J501, U401, U402, and U403. Among them,

[0066] The A2 terminal of chip U401 is connected to resistor R401. The A1 terminal of chip U401 is connected to resistor R402. The A0 terminal of chip U401 is connected to resistor R403. The RESET terminal of chip U401 is connected to resistor R404. Resistor R404 is connected to the PP5V terminal. Resistors R401, R402, and R403 are all grounded;

[0067] The VSS terminal of chip U401 is grounded. The VDD terminal of chip U401 is connected to capacitor C401 and also connected to the PP5V terminal. Capacitor C401 is grounded. The SCK terminal of chip U401 is connected to the SCL2 terminal of chip U403 and also connected to resistor R408. The SI terminal of chip U401 is connected to the SDA2 terminal of chip U403 and also connected to resistor R407. Resistor R407 is connected to the other end of resistor R408 and also connected to the PP5V terminal;

[0068] The GP0 terminal of chip U401 is connected to the I1 terminal of chip U402. The GP1 terminal of chip U401 is connected to the I2 terminal of chip U402. The GP2 terminal of chip U401 is connected to the I3 terminal of chip U402. The GP3 terminal of chip U401 is connected to the I4 terminal of chip U402. The GP4 terminal of chip U401 is connected to the I5 terminal of chip U402. The GP5 terminal of chip U401 is connected to the I6 terminal of chip U402. The GP6 terminal of chip U401 is connected to the I7 terminal of chip U402;

[0069] The VDD1 terminal of chip U403 is connected to capacitor C403 and also connected to the I2C_PWR terminal. Capacitor C403 is grounded. The GND1 and GND2 terminals of chip U403 are grounded. The VDD2 terminal of chip U403 is connected to capacitor C404 and also connected to the PP5V terminal. Capacitor C404 is grounded;

[0070] The SDA1 terminal of chip U403 is connected to pin 12 of chip J501 and also connected to dual Schottky diode D502. The SCL1 terminal of chip U403 is connected to pin 10 of chip J501 and also connected to dual Schottky diode D501.

[0071] In this circuit, chip U401 is an 8-bit IO control chip with I2C communication function. In this embodiment, the MCP23008-E / ML type is preferably adopted. Chip U402 is a driver chip. In this embodiment, the TBD62083AFWG type is preferably adopted. Chip U403 is a digital signal isolation module. In this embodiment, the ADuM1251ARZ-RL7 type is preferably adopted. Chip J501 is a signal chip. In this embodiment, the FCM2431-1001B01B1AB is preferably adopted. And in this embodiment, the dual Schottky diodes D501 and D502 are preferably of the BAT54SLT1G type. An external controller (MCU, PC, Raspberry Pi, etc.) can control the IO through the I2C bus, thereby controlling the current switching relay to switch different output currents.

[0072] The current switching circuit includes six relay circuits. The constant voltage source is connected to the relay circuits, and the relay circuits are connected to the feedback circuit and the protection circuit.

[0073] The specific circuit structure includes resistors R305, R309, E312, R317, R320 connected to the OUT terminal of chip U303, and six-way relays including K301, K302, K304, K305, K306, K307. Among them,

[0074] Pin 1 of relay K301 is connected to resistor R304 and to the PP5V terminal. Pin 3 of relay K301 is connected to resistor R303, and resistor R303 is grounded. Pins 4 and 5 of relay K301 are connected to the CC_OUT terminal. Pin 6 of relay K301 is connected to resistor R302 and to the ADJ / GND terminal of chip U301. Resistor R302 is connected to the OUT terminal of chip U301. The IN terminal of chip U301 is connected to resistor R301, and resistor R301 is connected to capacitor C301 and to the PP5V terminal. Capacitor C301 is grounded. Pin 8 of relay K301 is connected to the O6 terminal of chip U402 and to the negative pole of diode D301. The positive pole of diode D301 is connected to the other end of resistor R304.

[0075] Pin 1 of relay K302 is connected to resistor R308 and to the PP5V terminal. Pin 3 of relay K302 is connected to resistor R306, and resistor R306 is grounded. Pins 4 and 5 of relay K302 are connected to the CC_OUT terminal. Pin 6 of relay K302 is connected to resistor R305. Pin 8 of relay K302 is connected to the O5 terminal of chip U402 and to the negative pole of diode D303. The positive pole of diode D303 is connected to the other end of resistor R308.

[0076] The circuit connection structures of relays K304, K305, K306, K307 and resistors R309, E312, R317, R320 are similar to the circuit connection structure of relay K302 and resistor R305, and will not be elaborated here.

[0077] This circuit mainly controls six current loops through 6 mechanical relays respectively. The resistance values of the current-limiting resistors in each current loop are different, so as to achieve six different current outputs.

[0078] The feedback circuit includes chip U305.

[0079] The negative terminal and OUT terminal of chip U305 are connected to the REF terminal of chip U303.

[0080] The positive terminal of chip U305 is connected to resistor R324 and to the CC_OUT terminal of the relay loop. Resistor R324 is connected to capacitor C308 and grounded.

[0081] The V- terminal of chip U305 is connected to capacitor C311 and to the PN12V terminal. Capacitor C311 is grounded.

[0082] The V+ terminal of chip U305 is connected to the other end of capacitor C308 and to the PP12V terminal.

[0083] In this circuit, chip U305 is an operational amplifier, preferably of the LF356MX / NOPB type. Chip U305 collects the output voltage and feeds it back to chip U303 to ensure the stability of the constant voltage source output and improve the output capacity of the constant voltage source.

[0084] The protection circuit includes relay K303 and chip U302.

[0085] Pin 1 of relay K303 is connected to resistor R307 and then to the PP5V terminal. Resistor R307 is connected to light-emitting diode D302, and light-emitting diode D302 is connected to pin 8 of relay K303 and also to the O7 terminal of chip U402.

[0086] Pin 3 of relay K303 is connected to the positive electrode of diode D304 and then to the IN- terminal of chip U302. Diode D304 is connected to the VOUT terminal of chip U302.

[0087] Pin 4 of relay K303 is connected to the CC_OUT terminal of the relay circuit.

[0088] The V- terminal of chip U302 is connected to capacitor C303 and then to the PN12V terminal, and capacitor C303 is grounded.

[0089] The IN+ terminal of chip U302 is connected to resistors R314 and R315. Resistor R314 is connected to capacitor C304 and then to the PN12V terminal, capacitor C304 is grounded, resistor R315 is connected to capacitor C305 and then to the PN12V terminal, and capacitor C305 is grounded.

[0090] The V+ terminal of chip U302 is connected to capacitor C302 and then to the PP12V terminal, and capacitor C302 is grounded.

[0091] In this circuit, chip U302 is an operational amplifier. In this embodiment, the AD8065ARTZ-REEL type is preferably used. The function of this circuit is to connect chip U302 to the constant current circuit through relay K303, which can limit the voltage to about 4.5V and protect the subsequent circuit from being burned out.

[0092] The principle of this product is that the external controller controls the relay through I2C communication to switch the current gear, and it has the following advantages:

[0093] 1. The test is stable and accurate. The analog circuit and the digital circuit are separated, and the system works stably.

[0094] 2. Multi-channel automatic switching, simple operation.

[0095] 3. The core functions have been verified through a large number of tests and are stable in use.

[0096] 4. Small size and simple wiring

[0097] Overcomes the shortcomings of the prior art, achieving low cost, small volume, miniaturization, lightweight, and modular design.

[0098] The above shows and describes the basic principles, main features and advantages of the present utility model. Those skilled in the art should understand that the present utility model is not limited by the above embodiments. The above embodiments and the descriptions in the specification are only preferred examples of the present utility model and are not used to limit the present utility model. Without departing from the spirit and scope of the present utility model, the present utility model will have various changes and improvements, and these changes and improvements all fall within the scope of the present utility model claimed. The scope of protection claimed by the present utility model is defined by the appended claims and their equivalents.

Claims

1. A constant current source module for resistance measurement, characterized in that: It includes a current stabilizing unit and a switching unit. The current stabilizing unit includes a constant voltage source, a protection circuit and a feedback circuit. The switching unit includes a current switching circuit and a relay control circuit. The constant voltage source and the relay control circuit are both connected to the current switching circuit. The current switching circuit is connected to the protection circuit and the feedback circuit. The feedback circuit is connected to the constant voltage source; The constant voltage source provides current for the current switching circuit. The external controller controls the current switching circuit to switch the output current through the relay control circuit, and the feedback circuit collects the current and feeds it back to the constant voltage source to ensure the stability of the current output.

2. The constant current source module for resistance measurement according to claim 1, characterized in that: The constant voltage source includes chips U303 and U304, where, The REF terminal of chip U303 is connected to the AMP_REF terminal; The negative terminal of chip U303 is connected to capacitor C310 and grounded; The V- terminal of chip U303 is connected to the PN12V terminal and the other end of capacitor C310; The SENSE terminal of chip U303 is connected to the OUT terminal of chip U303 and the AMP_OUT terminal; The V+ terminal of chip U303 is connected to capacitor C307 and the PP12V terminal, and capacitor C307 is grounded; The positive terminal of chip U303 is connected to the OUT terminal of chip U304 and capacitor C309; The IN terminal of chip U304 is connected to resistor R323. Resistor R323 is connected to capacitor C306 and the PP5V terminal, and capacitor C306 is grounded; The GND terminal of chip U304 is connected to the other end of capacitor C309 and grounded.

3. The constant current source module for resistance measurement according to claim 1, wherein: The relay control circuit includes chips J501, U401, U402 and U403, where, The A2 terminal of chip U401 is connected to resistor R401. The A1 terminal of chip U401 is connected to resistor R402. The A0 terminal of chip U401 is connected to resistor R403. The RESET terminal of chip U401 is connected to resistor R404. Resistor R404 is connected to the PP5V terminal. Resistors R401, R402 and R403 are all grounded; The VSS terminal of chip U401 is grounded. The VDD terminal of chip U401 is connected to capacitor C401 and the PP5V terminal. Capacitor C401 is grounded. The SCK terminal of chip U401 is connected to the SCL2 terminal of chip U403 and resistor R408. The SI terminal of chip U401 is connected to the SDA2 terminal of chip U403 and resistor R407. Resistor R407 is connected to the other end of resistor R408 and the PP5V terminal; The GP0 terminal of the chip U401 is connected to the I1 terminal of the chip U402, the GP1 terminal of the chip U401 is connected to the I2 terminal of the chip U402, the GP2 terminal of the chip U401 is connected to the I3 terminal of the chip U402, the GP3 terminal of the chip U401 is connected to the I4 terminal of the chip U402, the GP4 terminal of the chip U401 is connected to the I5 terminal of the chip U402, the GP5 terminal of the chip U401 is connected to the I6 terminal of the chip U402, and the GP6 terminal of the chip U401 is connected to the I7 terminal of the chip U402; The VDD1 terminal of the chip U403 is connected to the capacitor C403 and to the I2C_PWR terminal, the capacitor C403 is grounded, the GND1 and GND2 terminals of the chip U403 are grounded, the VDD2 terminal of the chip U403 is connected to the capacitor C404 and to the PP5V terminal, and the capacitor C404 is grounded; The SDA1 terminal of the chip U403 is connected to the 12th pin of the chip J501 and to the double Schottky diode D502, and the SCL1 terminal of the chip U403 is connected to the 10th pin of the chip J501 and to the double Schottky diode D501.

4. The constant current source module for resistance measurement according to claim 3, wherein: The current switching circuit includes a six-way relay circuit, the constant voltage source is connected to the relay circuit, and the relay circuit is connected to the feedback circuit and the protection circuit.

5. The constant current source module for resistance measurement according to claim 4, wherein: The feedback circuit includes the chip U305, The negative terminal and the OUT terminal of the chip U305 are connected to the REF terminal of the chip U303; The positive terminal of the chip U305 is connected to the resistor R324 and to the relay circuit, and the resistor R324 is connected to the capacitor C308 and grounded; The V- terminal of the chip U305 is connected to the capacitor C311 and to the PN12V terminal, and the capacitor C311 is grounded; The V+ terminal of the chip U305 is connected to the other end of the capacitor C308 and to the PP12V terminal.

6. The constant current source module for resistance measurement according to claim 4, wherein: The protection circuit includes the relay K303 and the chip U302, The 1st pin of the relay K303 is connected to the resistor R307 and to the PP5V terminal, the resistor R307 is connected to the light-emitting diode D302, and the light-emitting diode D302 is connected to the 8th pin of the relay K303 and to the O7 terminal of the chip U402; The 3rd pin of the relay K303 is connected to the positive electrode of the diode D304 and to the IN- terminal of the chip U302, and the diode D304 is connected to the VOUT terminal of the chip U302; The 4th pin of the relay K303 is connected to the relay circuit; The V- terminal of the chip U302 is connected to the capacitor C303 and to the PN12V terminal, and the capacitor C303 is grounded; The IN+ terminal of the chip U302 is connected to the resistors R314 and R315, the resistor R314 is connected to the capacitor C304 and to the PN12V terminal, the capacitor C304 is grounded, the resistor R315 is connected to the capacitor C305 and to the PN12V terminal, and the capacitor C305 is grounded; The V+ terminal of the chip U302 is connected to the capacitor C302 and to the PP12V terminal, and the capacitor C302 is grounded.

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