Peltier automatic switching cold and hot adjusting system

Abstract

The utility model relates to a Peltier automatic switching cold and hot adjusting system. The Peltier automatic switching cold and hot adjusting system comprises an MCU, and a temperature sensor, an operational amplifier and a motor driving chip which are respectively and electrically connected with the MCU, the operational amplifier is connected with the motor driving chip through the power supply circuit; the motor driving chip is connected with the temperature sensor through Peltier; the device is reasonable in design, compact in structure and convenient to use.

Description

Technical Field

[0001] The utility model relates to a Peltier automatic switching hot and cold regulating system. The Peltier can meet the switching needs of heating and cooling functions. The Peltier power is adjustable and the service life of the Peltier is effectively extended. Background Art

[0002] The semiconductor cooling sheet Peltier (hereinafter referred to as "Peltier") currently available on the market can realize the functions of forward current heating and reverse current cooling.

[0003] When using Peltier diodes, most users only implement one of the heating or cooling functions, and the heating or cooling power is not controllable. Some users can achieve Peltier power control, but they use power electronic switches to control the power by controlling the on-off frequency of the internal MOS tube.

[0004] Traditional Peltier devices used in industrial products can only achieve one of the following functions: heating or cooling. The power is uncontrollable, resulting in uncontrolled heating or cooling temperatures. Some Peltier devices use power electronics to control the Peltier's operating power, which only allows for one of the two functions. Furthermore, the power is constantly switched on and off by the device's internal MOS transistors, which can damage both the device and the Peltier device over time.

[0005] Explanation of the name: H-bridge: An electronic circuit that reverses the voltage or current across its connected load or output terminals. This circuit is used in most DC-AC converters (such as inverters and frequency converters) and some DC-DC converters (push-pull converters) used in power conversion. Peltier: A Peltier circuit achieves heating when current flows from one direction to the other and cooling when the current reverses. Utility Model Content

[0006] The technical problem to be solved by the present invention is generally to provide a Peltier automatic switching hot and cold regulation system, which can not only meet the switching between Peltier heating and cooling modes, but also make the Peltier power controllable so that the temperature reaches the set temperature requirement, and can effectively increase the service life of components and Peltier, ensuring that the circuit design can be used stably for a long time.

[0007] In order to solve the above problems, the technical solution adopted by the present invention is:

[0008] A Peltier automatic switching hot and cold regulating system includes an MCU and a temperature sensor, an operational amplifier, and a motor driver chip electrically connected to the MCU; the operational amplifier is connected to the motor driver chip through a power circuit;

[0009] The motor driver chip is connected to the temperature sensor through Peltier.

[0010] Furthermore, the power circuit includes a power chip U6 , a control voltage follower circuit electrically connected to the power chip U6 , and a Peltier voltage control circuit.

[0011] Furthermore, in the power chip U6, pin 7 is connected to 24V and grounded through capacitors C20-C22, and pins 6 and 9 are grounded;

[0012] The Peltier voltage control circuit includes a diode D5, capacitors C17-19, and an inductor L1. Capacitor C17 is connected between pins 7 and 8 of the power chip U6. One output of pin 8 is grounded through a diode D5, and the other output is filtered by an inductor L1 and parallel capacitors C18 and C19 before being connected to V-out.

[0013] Furthermore, the control voltage follower circuit includes an op amp U5A; pin 3 of the op amp U5A is connected to the Peltier-DA-CTR for electrical connection to the MCU, pin 3 is grounded through a capacitor, pin 2 is grounded through a resistor R17, and a resistor R18 is connected between pins 1 and 2; pin 4 is grounded, and pin 8 is connected to a voltage of +5V and then to ground through a capacitor C18; pin 1 is connected to pin 4 of the power chip U6 through resistors R21 and R103, and pin 1 of the op amp U5A is grounded through a parallel resistor R23 and a capacitor C13; pin 4 is grounded through a resistor R104.

[0014] Furthermore, the DAC pin of the MCU outputs a Peltier-DA-CTR voltage signal to the non-inverting terminal of the operational amplifier U6A; the Peltier-DA-CTR voltage output signal is recorded as DA-CTR.

[0015] Furthermore, the reference voltage of the power chip U6 includes VSENSE.

[0016] Furthermore, V-OUT output by the voltage chip U6 is connected to pin 11 of the motor driver chip U3 as the voltage source of the chip.

[0017] In the motor driver chip U3, pins 1 and 2 are connected to the pull-down circuit through the corresponding 8874-IN1 and 8874-IN2 respectively; pin 4 is externally connected to a high-level enable, and pin 4 is connected to the fault detection circuit through 8874-FAULT; pin 5 enters the external reference voltage input through 8874-VREF; pin 6 is connected to the circuit output and grounded through resistor R14, pin 7 is grounded, pins 8 and 10 are connected to the 8874-out1 channel and 8874-out2 channel respectively, pins 9, 15, and 17 are grounded, pin 16 is connected to +5V through resistor R6 and grounded through resistor R11, and pin 16 is connected to the NC channel; capacitor C5 is connected between pins 13 and 14, and capacitor C6 is connected between pin 12 and pin C11 through the VCP channel; pin 11 is grounded through parallel capacitors C7 and C8;

[0018] The fault detection circuit includes a resistor R15 connected in series between the 8874-FAULT channel and 5V and a light LED1.

[0019] Furthermore, the 8874-IN1 channel and the 8874-IN2 channel are connected to the IN1 control circuit and the IN2 control circuit respectively;

[0020] The IN1 control circuit includes an optocoupler chip U1. In the optocoupler chip U1, pin 1 is connected to a 3.3V voltage through a resistor R2, pin 3 is connected to the MCU, pin 6 is connected to 5V and grounded through a capacitor C1, pin 4 is grounded, pin 4 is connected to one end of a diode ID1, and pin 5 is connected to a resistor R5; the other end of the diode ID1 is connected to the 8874-IN1 channel; the output end of the resistor R5 is connected to the 8874-IN1 channel and to 5V through a resistor R1;

[0021] The 8874-IN1 channel is also grounded through capacitor C3;

[0022] The IN2 control circuit includes an optocoupler chip U2. In the optocoupler chip U2, pin 1 is connected to a 3.3V voltage through a resistor R4, pin 3 is connected to the MCU, pin 6 is connected to 5V and grounded through a capacitor C2, pin 4 is grounded, pin 4 is connected to one end of a diode ID2, and pin 5 is connected to a resistor R6; the other end of the diode ID2 is connected to the 8874-IN2 channel; the output end of the resistor R6 is connected to the 8874-IN2 channel and to 5V through a resistor R3;

[0023] The 8874-IN2 channel is also grounded through capacitor C4;

[0024] The motor driver chip U3 is electrically connected to an enabling circuit and an external reference voltage circuit;

[0025] The enable circuit includes resistors R8 and R13 connected to the 8874-SLEEP channel, which are connected to the 5V power supply and ground respectively. The voltage connected to pin 3 of the motor driver chip U3 is (5V*R13 / (R8*R13)).

[0026] The external reference voltage circuit includes resistors R7 and R12 connected to pin 4 of the motor driver chip through the 8874-VREF channel. Resistors R7 and R12 are connected to the power supply 5V and ground respectively;

[0027] The MCU controls the pull-up or pull-down of signals MCU-ENIN1 and MCU-ENIN2 to control the voltage levels of Pins 1 and 2 of the motor driver chip U3. The motor driver chip U3 internally houses an H-bridge consisting of four MOS transistors. External pins Pins 1 and 2 control the G electrodes of the MOS transistors, thereby switching the MOS transistors on and off, enabling forward or reverse current flow.

[0028] A Peltier-controlled automatic hot / cold switching method is disclosed, utilizing the aforementioned system. The following steps are performed: First, in the Peltier-DA-CTR voltage signal, the DAC pin of the microcontroller outputs an adjustable voltage of 0-3.3V; then, the adjustable voltage is amplified by the op amp U5A and becomes an adjustable voltage of 0-6.6V, denoted as DA-CTR; second, in the power supply chip U6, based on the superposition theorem, V-OUT is fed to the power supply pin of the motor driver chip U3, and the voltage output by the motor driver chip U3 is equal to VOUT; subsequently, the output voltage of the motor driver chip U3 is output via two pins 8 and 10 of the driver chip U3 and is determined by pins 1 and 2.

[0029] Furthermore, the output of the driver chip U3 is divided into three situations:

[0030] Case A, OUT1 and OUT2 are both equal to 0;

[0031] In case B, OUT1 outputs positive voltage and OUT2 outputs GND;

[0032] In case C, OUT2 outputs positive voltage and OUT1 outputs GND;

[0033] Among them, MCU controls the high and low levels of the GPIO pins, controls the high and low levels of pins 1 and 2 of the motor driver chip U3, and further controls the three output modes of the motor driver chip U3;

[0034] The ambient temperature is then measured by a temperature sensor and transmitted to the MCU. The MCU determines the output DAC value based on the set temperature value and the measured temperature value.

[0035] The ambient temperature obtained by the temperature sensor is Tget, and the set ambient temperature is Tflag. Based on the superposition theorem, a circuit with linearly adjustable voltage output is constructed. This not only controls the Peltier heating or cooling power but also extends the life of the Peltier and circuit components. This complete design solution allows for automatic switching between Peltier heating and cooling, and automatic power adjustment.

[0036] First, the MCU obtains the ambient temperature Tget through the temperature sensor; then, the MCU compares the obtained ambient temperature Tget with the set ambient temperature Tflag;

[0037] If the obtained ambient temperature Tget is greater than the set ambient temperature Tflag, the output cooling control is performed, ENIN1 is low and ENIN2 is high. At the same time, according to the difference between Tget and Tflag, the PID adjusts the DAC output of the MCU, that is, the Peltier-DA-CTR signal;

[0038] If the obtained ambient temperature Tget is lower than the set ambient temperature Tflag, output heating control is performed, and the motor driver chip U6 heats the DAC output PID to adjust the Peltier.

[0039] The utility model constructs a circuit with linearly adjustable voltage output based on the superposition theorem, which can not only control the power of Peltier heating or cooling, but also extend the service life of Peltier and circuit components.

[0040] The utility model has a complete design scheme in which Peltier heating and cooling can be automatically switched and power can be automatically adjusted.

[0041] The utility model has the advantages of reasonable design, low cost, durability, safety and reliability, simple operation, time and labor saving, money saving, compact structure and easy use. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 This is a schematic diagram of a voltage linearly adjustable circuit of the present utility model.

[0043] Figure 2 This is a schematic diagram of the IN1 control circuit of the present utility model.

[0044] Figure 3 This is a schematic diagram of the IN2 control circuit of the present utility model.

[0045] Figure 4 It is a schematic diagram of the peripheral circuit of the utility model.

[0046] Figure 5 This is a schematic diagram of the H1 bridge control circuit of the present utility model.

[0047] Figure 6 This is a schematic diagram of the logic control circuit of the present utility model.

[0048] Figure 7 This is a circuit block diagram of the utility model.

[0049] Figure 8 This is the internal logic processing diagram of the MCU of the utility model.

[0050] Figure 9 This is a schematic diagram of the forward drive of the utility model.

[0051] Figure 10 It is a reverse schematic diagram of the utility model. DETAILED DESCRIPTION

[0052] like Figure 1-10 , specifically Figure 8 , the system of this embodiment includes an MCU; the MCU is electrically connected to a temperature sensor, an op amp and a motor driver chip, and the op amp is connected to the motor driver chip through a power circuit;

[0053] The motor driver chip is connected to the temperature sensor via Peltier;

[0054] like Figure 8 The sequence numbers mark the signal flow, (1) the MCU outputs a controllable analog voltage to the op amp;

[0055] (2) The op amp follows the controllable analog voltage value and increases the signal strength before sending it to the power chip.

[0056] (3) The power chip outputs a linearly variable power voltage value to the motor driver chip.

[0057] (4) The MCU outputs high and low levels to control the suspension, heating, and cooling states of the Peltier through the motor driver chip.

[0058] (5) The motor driver chip outputs a voltage to the Peltier sensor that can control power and change the direction of current.

[0059] (6) The operation of the Peltier diode causes the ambient temperature to change, and the ambient temperature information is captured by the temperature sensor.

[0060] (7) The temperature sensor transmits the temperature information to the MCU.

[0061] like Figure 1 , the power supply circuit includes a power supply chip U6 and a control voltage follower circuit and a Peltier voltage control circuit electrically connected to the power supply chip U6;

[0062] In the power chip U6, pin 7 is connected to 24V and grounded through capacitors C20-C22, and pins 6 and 9 are grounded;

[0063] The Peltier voltage control circuit includes a diode D5, capacitors C17-19, and an inductor L1. Capacitor C17 is connected between pins 7 and 8 of the power chip U6. One output from pin 8 is grounded through diode D5, and the other output is filtered by inductor L1 and parallel capacitors C18 and C19 before being connected to V-out.

[0064] The control voltage follower circuit includes an op amp U5A; pin 3 of the op amp U5A is connected to a Peltier-DA-CTR for electrical connection to the MCU, pin 3 is grounded via a capacitor, pin 2 is grounded via a resistor R17, and a resistor R18 is connected between pins 1 and 2; pin 4 is grounded, and pin 8 is connected to a voltage of +5V and then to ground via a capacitor C18; pin 1 is connected to pin 4 of the power chip U6 via resistors R21 and R103, and pin 1 of the op amp U5A is grounded via a parallel resistor R23 and capacitor C13; pin 4 is grounded via a resistor R104;

[0065] The MCU's DAC pin outputs a "Peltier-DA-CTR" voltage signal to the non-inverting terminal of operational amplifier U6A. Based on the op amp's peripheral resistor configuration (R17 = 10K, R18 = 10K), the Peltier-DA-CTR voltage signal is amplified by 100% and then output as DA-CTR.

[0066] The MCU outputs a Peltier-DAC analog voltage value. To prevent interference with this analog signal, an external op amp (MCP6002) is connected to the DAC output to enhance signal stability. Voltage amplification is based on the characteristics of the op amp, and the gain is determined by the resistor values ​​of the peripheral circuits. The output voltage of the DAC pin is continuously adjustable. When the DAC pin output voltage varies, the V-OUT value (described below) also varies linearly within a certain range.

[0067] By building the above voltage linear adjustment, the heating or cooling power can be adjusted, and the current direction can be switched to achieve the switching of heating or cooling. Through the controllable voltage source, the temperature can reach the desired temperature requirement, such as Figure 7 Feedback regulation is formed by a sensor specially used to measure temperature and a Peltier resistor. Since the output of the voltage source is ripple-processed, the output voltage value changes smoothly. Ripple processing is achieved through inductance and capacitance, but the role of ripple processing is secondary; the main reason is that the continuous on-off regulation of PWM is different from the continuous on-off process of the duty cycle, which can effectively extend the service life of the Peltier resistor and circuit components.

[0068] VSENSE is a reference voltage for power chip U6. This reference voltage has excellent stability and minimal temperature drift, acting as a constant voltage source. The DA-CRT signal is another voltage source controlled by the MCU. According to the design of the power chip, its output, V-OUT, is dependent on voltage source VSENSE, voltage source DC-CTR, resistors R101 (which fine-tunes the voltage), R102, R103, and R104.

[0069] Since the circuit components of the output part of the power supply chip are all composed of resistors, this part is a linear circuit; and because the reference voltage VSNSE of the power supply chip is a constant voltage source, and DA-CTR is a controlled linearly changing voltage source, according to the superposition theorem (when one independent source is constant and an independent source changes linearly, then the response also changes linearly), it can be seen that the output voltage V-OUT of the power supply chip also changes linearly within a certain controlled range.

[0070] From the superposition theorem, we can get: V-OUT * (R103 / / R104) / [(R101+R102) / / (R103 / / R104)] + DC-CRT * [(R101+R102) / / R104] / {[(R101+R102) / / R104]+R103} = VSENSE = 1.221 (constant value);

[0071] like Figure 2-Figure 6 The V-OUT output of the voltage chip U6 is connected to the pin 11 of the motor driver chip U3 as the voltage source of the chip.

[0072] In the motor driver chip U3, pins 1 and 2 are connected to the pull-down circuit through the corresponding 8874-IN1 and 8874-IN2 respectively; pin 4 is externally connected to a high-level enable, and pin 4 is connected to the fault detection circuit through 8874-FAULT; pin 5 enters the external reference voltage input through 8874-VREF; pin 6 is connected to the circuit output and grounded through resistor R14, pin 7 is grounded, pins 8 and 10 are connected to the 8874-out1 channel and 8874-out2 channel respectively, pins 9, 15, and 17 are grounded, pin 16 is connected to +5V through resistor R6 and grounded through resistor R11, and pin 16 is connected to the NC channel; capacitor C5 is connected between pins 13 and 14, and capacitor C6 is connected between pin 12 and pin C11 through the VCP channel; pin 11 is grounded through parallel capacitors C7 and C8;

[0073] The 8874-IN1 channel and the 8874-IN2 channel are connected to the IN1 control circuit and the IN2 control circuit respectively;

[0074] The IN1 control circuit includes an optocoupler chip U1. In the optocoupler chip U1, pin 1 is connected to a 3.3V voltage through a resistor R2, pin 3 is connected to the MCU, pin 6 is connected to 5V and grounded through a capacitor C1, pin 4 is grounded, pin 4 is connected to one end of a diode ID1, and pin 5 is connected to a resistor R5; the other end of the diode ID1 is connected to the 8874-IN1 channel; the output end of the resistor R5 is connected to the 8874-IN1 channel and to 5V through a resistor R1;

[0075] The 8874-IN1 channel is also grounded through capacitor C3;

[0076] The IN2 control circuit includes an optocoupler chip U2. In the optocoupler chip U2, pin 1 is connected to a 3.3V voltage through a resistor R4, pin 3 is connected to the MCU, pin 6 is connected to 5V and grounded through a capacitor C2, pin 4 is grounded, pin 4 is connected to one end of a diode ID2, and pin 5 is connected to a resistor R6; the other end of the diode ID2 is connected to the 8874-IN2 channel; the output end of the resistor R6 is connected to the 8874-IN2 channel and to 5V through a resistor R3;

[0077] The 8874-IN2 channel is also grounded through capacitor C4;

[0078] like Figure 1 First, in the Peltier-DA-CTR voltage signal, the DAC pin of the microcontroller outputs an adjustable voltage of 0-3.3V; then, the voltage is amplified by the op amp U5A by 1 times and becomes an adjustable voltage of 0-6.6V, recorded as DA-CTR; secondly, because DA-CTR is adjustable within a certain range, in the power chip U6, the superposition theorem shows that V-OUT is adjustable within a certain range. Again, as Figure 5 , V-OUT is given to the power supply pin of the motor driver chip U3, and the voltage output by the chip is equal to VOUT. Later, the output voltage of the motor driver chip U3 is obtained by Figure 5 There are three situations for the outputs of the two pins 8 and 10: (1) OUT1 and OUT2 are both equal to 0; (2) OUT1 outputs a positive voltage (equal to the V-OUT value connected to pin 11), and OUT2 outputs GND. (3) OUT2 outputs a positive voltage (equal to the V-OUT value connected to pin 11), and OUT1 outputs GND; combined with Figure 6 The three output conditions of the motor driver chip U3 are determined by pins 1 and 2. Specifically, if Figure 2 、 3 , the MCU controls the high and low levels of these two GPIO pins, controls the high and low levels of pins 1 and 2 of the motor driver chip U3, and then controls the three output modes of the motor driver chip U3; then the ambient temperature is measured by the temperature sensor and the temperature value is transmitted to the MCU. The MCU determines the size of the output DAC according to the set temperature value and the measured temperature value.

[0079] like Figure 4 The enabling circuit includes resistors R8 and R13 connected to the 8874-SLEEP channel respectively, and resistors R8 and R13 are connected to the power supply 5V and ground respectively; the resistors R8 and R13 are used to set the resistor division voltage: among which, the voltage connected to pin 3 of the motor driver chip is (5V*R13 / (R8*R13)).

[0080] like Figure 4 , the external reference voltage circuit includes resistors R7 and R12 connected to pin 4 of the motor driver chip through the 8874-VREF channel, and resistors R7 and R12 are connected to the power supply 5V and ground respectively;

[0081] The fault detection circuit includes resistor R15 connected in series between the 8874-FAULT channel and 5V and the light LED1;

[0082] In general, the MCU control signals MCU-ENIN1 and MCU-ENIN2 are pulled high or low to control the level states of Pin1 and Pin2 of the motor driver chip U3. The interior of the motor driver chip U3 is an H-bridge composed of four MOS tubes. The G pole of the MOS tube is controlled by the external pins Pin1 and Pin2, thereby controlling the on and off of the MOS tube to achieve forward or reverse current flow, that is, the heating function or cooling function of the Peltier.

[0083] According to the output logic control of the motor driver chip DRV8874 (U3) in the attached figure, the MCU only needs to simply pull it high or low to switch between heating and cooling functions.

[0084] In the process Figure 8 In Chinese: Tget is the ambient temperature obtained by the temperature sensor, and Tflag is the set ambient temperature. Based on the superposition theorem, building a circuit with linearly adjustable voltage output not only controls the Peltier heating or cooling power but also extends the life of the Peltier and circuit components. This complete design solution allows for automatic switching between Peltier heating and cooling, with automatic power regulation.

[0085] First, the MCU obtains the ambient temperature Tget through the temperature sensor; then, the MCU compares the obtained ambient temperature Tget with the set ambient temperature Tflag;

[0086] If the obtained ambient temperature Tget is greater than the set ambient temperature Tflag, the output cooling control is performed, ENIN1 is low and ENIN2 is high. At the same time, according to the difference between Tget and Tflag, the PID adjusts the DAC output of the MCU, that is, the Peltier-DA-CTR signal;

[0087] If the obtained ambient temperature Tget is lower than the set ambient temperature Tflag, output heating control is performed, and the motor driver chip U6 heats the DAC output PID to adjust the Peltier.

[0088] The present invention is fully described for the purpose of clearer disclosure, and the prior art will not be listed one by one.

[0089] Finally, it should be noted that the above embodiments are intended only to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may be modified or some of the technical features thereof may be replaced with equivalents. It is obvious for those skilled in the art to combine multiple technical solutions of the present invention. However, these modifications or replacements do not deviate from the spirit and scope of the technical solutions of the embodiments of the present invention. Any technical content not fully described in this utility model is generally known technology.

Claims

1. A Peltier system capable of automatically switching between hot and cold conditions, characterized in that: It includes an MCU and a temperature sensor, an operational amplifier and a motor driver chip electrically connected to the MCU; the operational amplifier is connected to the motor driver chip through a power circuit; The motor driver chip is connected to the temperature sensor through Peltier.

2. The Peltier automatic switching heating and cooling system according to claim 1, characterized in that: The power circuit includes a power chip U6 , a control voltage follower circuit electrically connected to the power chip U6 , and a Peltier voltage control circuit.

3. The Peltier automatic switching heating and cooling system according to claim 2, characterized in that: In the power chip U6, pin 7 is connected to 24V and grounded through capacitors C20-C22, and pins 6 and 9 are grounded; The Peltier voltage control circuit includes a diode D5, capacitors C17-19, and an inductor L1. Capacitor C17 is connected between pins 7 and 8 of the power chip U6. One output of pin 8 is grounded through a diode D5, and the other output is filtered by an inductor L1 and parallel capacitors C18 and C19 before being connected to V-out.

4. The Peltier automatic switching heating and cooling system according to claim 3, characterized in that: The control voltage follower circuit includes an op amp U5A; pin 3 of the op amp U5A is connected to a Peltier-DA-CTR for electrical connection to the MCU, pin 3 is grounded through a capacitor, pin 2 is grounded through a resistor R17, and a resistor R18 is connected between pins 1 and 2; pin 4 is grounded, and pin 8 is connected to a voltage of +5V and then to ground through a capacitor C18; pin 1 is connected to pin 4 of the power chip U6 through resistors R21 and R103, and pin 1 of the op amp U5A is grounded through a parallel resistor R23 and capacitor C13; pin 4 is grounded through a resistor R104.

5. The Peltier automatic switching heating and cooling system according to claim 4, characterized in that: The DAC pin of the MCU outputs a Peltier-DA-CTR voltage signal to the non-inverting terminal of the operational amplifier U6A; the Peltier-DA-CTR voltage output signal is recorded as DA-CTR.

6. The Peltier automatic switching heating and cooling system according to claim 5, characterized in that: The V-OUT output of the voltage chip U6 is connected to the pin 11 of the motor driver chip U3 as the voltage source of the chip.

7. The Peltier automatic switching heating and cooling system according to claim 5, characterized in that: In the motor driver chip U3, pins 1 and 2 are connected to the pull-down circuit through the corresponding 8874-IN1 and 8874-IN2 respectively; pin 4 is externally connected to a high-level enable, and pin 4 is connected to the fault detection circuit through 8874-FAULT; pin 5 enters the external reference voltage input through 8874-VREF; pin 6 is connected to the circuit output and grounded through resistor R14, pin 7 is grounded, pins 8 and 10 are connected to the 8874-out1 channel and 8874-out2 channel respectively, pins 9, 15, and 17 are grounded, pin 16 is connected to +5V through resistor R6 and grounded through resistor R11, and pin 16 is connected to the NC channel; capacitor C5 is connected between pins 13 and 14, and capacitor C6 is connected between pin 12 and pin C11 through the VCP channel; pin 11 is grounded through parallel capacitors C7 and C8.

8. The Peltier automatic switching heating and cooling system according to claim 7, characterized in that: The fault detection circuit includes a resistor R15 connected in series between the 8874-FAULT channel and 5V and a light LED1.

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