Piezoresistor protection circuit and air conditioner

Abstract

The utility model discloses a piezoresistor protection circuit and an air conditioner, and the piezoresistor protection circuit comprises a controller; the switching circuit is also used for connecting / disconnecting the first power supply end and the piezoresistor under the control of the controller; the overvoltage detection circuit is connected in series between the second end of the piezoresistor and the second power supply end, the controlled end of the overvoltage detection circuit is electrically connected with the controller, and the overvoltage detection circuit is used for sampling alternating current flowing through the piezoresistor and converting the alternating current into a corresponding detection voltage waveform when the piezoresistor is broken down due to overvoltage; the controller is also used for controlling the switching circuit to disconnect the piezoresistor and the first power supply end when continuously receiving the detection voltage waveform of the preset voltage value within a preset time period; according to the technical scheme of the utility model, the overvoltage of the piezoresistor can be accurately detected, and the piezoresistor can be timely protected at the same time.

Description

Technical Field

[0001] The utility model relates to the technical field of air conditioners, and particularly relates to a varistor protection circuit and an air conditioner. Background Art

[0002] At present, for lightning protection measures of air conditioner controllers on the market, a zinc oxide varistor is connected in parallel between the input power supply lines L and N. However, the varistor is also prone to thermal breakdown due to overvoltage of the power grid, and long-term connection will also cause the varistor to catch fire and burn. Existing varistor protection measures usually add a fuse tube or a gas discharge tube in the circuit. However, the fuse tube will not break when the current flowing through the varistor is less than the protection current value of the fuse tube, and it also takes a long response time for the gas discharge tube to drive the fuse tube to break by transferring high temperature. Summary of the Utility Model

[0003] The main purpose of the utility model is to provide a varistor protection circuit and an air conditioner, aiming to accurately detect overvoltage of the varistor and timely perform protection processing on the varistor.

[0004] To achieve the above purpose, the varistor protection circuit proposed by the utility model includes:

[0005] A controller;

[0006] A switch circuit, whose first connection end is used to connect to the first power supply end of the commercial power, whose second connection end is used to connect to the first end of the varistor, and whose controlled end is electrically connected to the controller. The switch circuit is also used to connect or disconnect the first power supply end and the varistor under the control of the controller;

[0007] An overvoltage detection circuit, which is connected in series between the second end of the varistor and the second power supply end, and whose controlled end is electrically connected to the controller. The overvoltage detection circuit is used to sample the alternating current flowing through the varistor when the varistor is overvoltage broken down, and convert it into a corresponding detected voltage waveform;

[0008] The controller is also used to control the switch circuit to disconnect the connection between the varistor and the first power supply end when it continuously receives the detected voltage waveform with a preset voltage value within a preset time period.

[0009] In some embodiments, the overvoltage detection circuit includes:

[0010] A sampling circuit, whose first sampling end is connected to the second end of the varistor, and whose second sampling end is connected to the second power supply end. The sampling circuit is used to sample the alternating current flowing through the varistor, perform voltage conversion and rectification processing, and output a corresponding DC sampling voltage;

[0011] A voltage stabilizing circuit is connected in series between the output end of the sampling circuit and the controller. The voltage stabilizing circuit is used to stabilize the DC sampling voltage and then output it as a detected voltage waveform.

[0012] In some embodiments, the sampling circuit includes:

[0013] An isolation circuit, the first end of its primary side is used to connect to the second end of the varistor, and the second end of its primary side is used to connect to the second power supply end of the mains. The isolation circuit is further used to couple the AC current when the varistor passes through the AC current, and then perform voltage conversion processing to output a corresponding AC sampling voltage;

[0014] A rectifying circuit is connected in series between the secondary side of the isolation circuit and the input end of the voltage stabilizing circuit. The rectifying circuit is used to rectify the AC sampling voltage and then output a corresponding DC sampling voltage.

[0015] In some embodiments, the isolation circuit includes:

[0016] A current transformer, having a first input pin, a second input pin, a first output pin and a second output pin. The first input pin is the first end of the primary side of the isolation circuit, the first output pin is the second end of the primary side of the isolation circuit, and the second end of the second output pin is grounded;

[0017] A first resistor is connected in parallel between the second input pin of the current transformer and the second output pin.

[0018] In some embodiments, the rectifying circuit includes:

[0019] A first diode, the anode of which is the input end of the rectifying circuit and the cathode of which is the output end of the rectifying circuit.

[0020] In some embodiments, the voltage stabilizing circuit includes:

[0021] A second resistor, the first end of which is the input end of the voltage stabilizing circuit;

[0022] A third resistor, the first end of which is connected to the second end of the second resistor and the second end of which is grounded.

[0023] A fourth resistor is connected in series between the second end of the second resistor and the controller;

[0024] A voltage stabilizing diode, the cathode of which is connected to the second end of the second resistor and the anode of which is grounded.

[0025] In some embodiments, the voltage stabilizing circuit further includes:

[0026] A first capacitor is connected in parallel across both ends of the voltage stabilizing diode;

[0027] A second capacitor is connected in parallel across both ends of the voltage stabilizing diode.

[0028] In some embodiments, the switching circuit includes:

[0029] A relay, including a contact and a coil. The first end of the contact is used to connect to the first power supply terminal, the second end of the contact is used to connect to the first end of the varistor, and the first end of the coil is used to connect to a power supply;

[0030] A switching transistor, whose input terminal is connected to the second end of the coil and whose output terminal is grounded;

[0031] A fifth resistor is connected in series between the controlled terminal of the switching transistor and the controller;

[0032] A sixth resistor is connected in parallel between the controlled terminal of the switching transistor and the output terminal of the switching transistor;

[0033] A second diode is connected in parallel across both ends of the coil.

[0034] In some embodiments, the varistor protection circuit further includes:

[0035] A fuse. The first end of the fuse is used to connect to the first power supply terminal, the second end of the fuse is used to connect to the input terminal of the switching circuit, and is also used to disconnect the connection between the first power supply terminal and the varistor when the maximum current value of the alternating current flowing through the varistor reaches the protection current value of the fuse.

[0036] The present utility model further provides an air conditioner, including a varistor and the above-mentioned varistor protection circuit, and the varistor is electrically connected to the varistor protection circuit.

[0037] The technical solution of the present utility model uses an overvoltage detection circuit to sample the alternating current flowing through the varistor when it is broken down by overvoltage, output a corresponding detected voltage waveform to the controller, and utilize the principle that the voltage output by the mains power supply system is a power frequency voltage, and continuously sample the alternating current with a preset time period as the detection period. Thus, when the varistor is broken down by overvoltage due to the disconnection of the neutral line, the controller will continuously receive the detected voltage waveform and control the switching circuit to disconnect the varistor from the first power supply terminal, reducing the risk of the varistor catching fire caused by the alternating current being less than the protection current value and the fuse not turning off, or the long response time of the gas discharge tube. It realizes accurate detection of the varistor overvoltage and timely protection of the varistor. Description of the Drawings

[0038] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the accompanying drawings required for use in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on the structures shown in these drawings.

[0039] Figure 1 Schematic diagram of the structure of an embodiment of the varistor protection circuit of the present invention;

[0040] Figure 2 Schematic diagram of the structure of another embodiment of the varistor protection circuit of the present invention;

[0041] Figure 3 Schematic diagram of the structure of yet another embodiment of the varistor protection circuit of the present invention;

[0042] Figure 4 Schematic diagram of the structure of still another embodiment of the varistor protection circuit of the present invention;

[0043] Figure 5 Circuit connection diagram of an embodiment of the varistor protection circuit of the present invention;

[0044] Figure 6 Schematic diagram of the mains power supply system when the neutral line is missing;

[0045] Figure 7 Waveform diagram of the mains current when the neutral line is missing;

[0046] Figure 8 Waveform diagram of the AC sampling voltage output by the isolation circuit;

[0047] Figure 9 Waveform diagram of the DC sampling voltage output by the rectification circuit;

[0048] Figure 10 Waveform diagram of the detection voltage waveform output by the voltage stabilization circuit.

[0049] Explanation of the reference numerals in the drawings:

[0050] Label Name Label Name 100 Controller ZR1 Varistor 200 Switching circuit L1 Current transformer 300 Overvoltage detection circuit KY1 Relay 310 Sampling circuit Q1 Switching transistor 311 Isolation circuit TZ1 Zener diode 312 Rectifier circuit D1~D2 First diode~Second diode 320 Voltage regulation circuit C1~C2 First capacitor~Second capacitor 400 Fuse R1~R6 First resistor~Sixth resistor

[0051] The realization of the object of the present invention, its functional features and advantages will be further described with reference to the embodiments and the accompanying drawings. Detailed implementation manners

[0052] The following will clearly and completely describe the technical solutions in the embodiments of the present utility model in conjunction with the accompanying drawings in the embodiments of 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. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present utility model without creative efforts shall fall within the protection scope of the present utility model.

[0053] In addition, in the present utility model, descriptions such as "first" and "second" are only for descriptive purposes, and cannot be understood as indicating or implying their relative importance or implicitly indicating the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include at least one such feature. In addition, the technical solutions between the various embodiments can be combined with each other, but it must be based on the ability of those of ordinary skill in the art to implement. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such a combination of technical solutions does not exist and is not within the protection scope required by the present utility model.

[0054] The present utility model provides a varistor protection circuit.

[0055] Referring to Figure 1 , in one embodiment, the varistor protection circuit includes:

[0056] A controller 100;

[0057] A switch circuit 200, whose first connection end is used to connect to the first power supply end of the mains power, whose second connection end is used to connect to the first end of the varistor, and whose controlled end is electrically connected to the controller 100. The switch circuit 200 is further configured to connect / disconnect the varistor from the first power supply end under the control of the controller 100.

[0058] An overvoltage detection circuit 300, which is connected in series between the second end of the varistor and the second power supply end, and whose controlled end is electrically connected to the controller 100. The overvoltage detection circuit 300 is configured to sample the alternating current flowing through the varistor and convert it into a corresponding detected voltage waveform when the varistor is overvoltage broken down.

[0059] The controller 100 is further configured to control the switch circuit 200 to disconnect the connection between the varistor and the first power supply end when the detected voltage waveform of the preset voltage value is continuously received within a preset time period.

[0060] It should be noted that as Figure 6As shown in the figure, in a three-phase four-wire mains power supply system, there are multiple live wire connection terminals U, V, and W, and a neutral wire connection terminal N in the middle. Under normal circumstances, a load is connected to any one of the live wire connection terminals and the neutral wire connection terminal respectively to form a closed loop of single-phase alternating current. At this time, the voltage applied across the load is the normal single-phase line voltage of 380V.

[0061] However, if the neutral wire of the mains power supply system is open due to reasons such as cable aging and external forces, when there are more than two loads connected to the power supply system and they are connected to different phases, the line voltage of one phase will be superimposed with the line voltage of the other phase of Load 1 and Load 2, and the maximum will reach more than 700V. Since the varistor bridging the first power supply terminal and the second power supply terminal of the air conditioner controller 100 usually uses a 620V level, the varistor will be thermally broken down at this time. A large current alternating current will flow through the thermistor, causing it to heat up, and it will catch fire and burn after a long connection.

[0062] In this embodiment, the first power supply terminal and the second power supply terminal of the mains power supply respectively represent the connection terminals of the neutral wire and the live wire. When the first power supply terminal is the connection terminal of the neutral wire, the second power supply terminal is the connection terminal of the live wire. When the first power supply terminal is the connection terminal of the live wire, the second power supply terminal is the connection terminal of the neutral wire.

[0063] Specifically, when the neutral wire of the mains power supply system is open, the varistor inputs an abnormal overvoltage and receives a power frequency voltage waveform as shown in Figure 7 the figure. At this time, the overvoltage (such as above 620V) will break down the varistor, causing the alternating current to form a current loop through the varistor, the overvoltage detection circuit 300 and the second power supply terminal. At this time, the overvoltage detection circuit 300 samples this part of the alternating current. Since the mains power supply is a power frequency voltage and the voltage frequency during overvoltage remains unchanged, there will be the same breakdown waveform in multiple power frequency cycles. That is, in each power frequency cycle, when overvoltage occurs, the same detection voltage waveform can be output according to the sampled alternating current.

[0064] It can be understood that in the case of lightning strikes, surges, etc., there will also be a short-term overvoltage that breaks down the varistor. However, this breakdown is instantaneous and will not be applied across the varistor for a long time, and the varistor will not heat up and catch fire due to this.

[0065] Therefore, a timer is also integrated in the controller 100 to measure time with a preset period as a detection cycle. If the detection voltage waveform is continuously detected within the preset period, it indicates that the overvoltage is a power frequency voltage, that is, the neutral line is disconnected at this time, and the two-phase line voltages are superimposed across the varistor. Continuous connection will cause the varistor to heat up and catch fire. Therefore, the controller 100 outputs a corresponding turn-off control signal to the switch circuit 200 to control the switch circuit 200 to disconnect the varistor from the first power supply terminal; if the detection voltage waveform is not continuously detected within the preset period, it indicates that the overvoltage is generated by lightning strike, that is, the neutral line is not disconnected at this time, and the varistor will not heat up and catch fire. Therefore, the controller 100 will not output a turn-off control signal to the switch circuit 200, and the switch circuit 200 keeps the varistor connected to the first power supply terminal.

[0066] Among them, the preset period is preset in the controller 100 by R & D personnel according to actual needs, and can be a period corresponding to 10 power frequency cycles, a period corresponding to 7 power frequency cycles, etc.

[0067] The technical solution of the present utility model adopts an overvoltage detection circuit 300 to sample the alternating current flowing through the varistor circuit when the varistor is broken down by overvoltage, output a corresponding detection voltage waveform to the controller 100, and utilize the principle that the voltage output by the mains power supply system is a power frequency voltage. With the preset period as the detection cycle, the alternating current is continuously sampled. Thus, when the varistor is broken down by overvoltage due to the disconnection of the neutral line, the controller 100 will control the switch circuit 200 to disconnect the varistor from the first power supply terminal due to continuously receiving the detection voltage waveform, reducing the varistor fire caused by the alternating current being less than the protection current value and the fuse tube not turning off, or the long response time of the gas discharge tube. It realizes accurate detection of the varistor overvoltage and timely protection of the varistor.

[0068] Refer to Figure 2 , in an embodiment, the overvoltage detection circuit 300 includes:

[0069] A sampling circuit 310, whose first sampling terminal is connected to the second terminal of the varistor, and whose second sampling terminal is connected to the second power supply terminal. The sampling circuit 310 is used to sample the alternating current flowing through the varistor, perform voltage conversion and rectification processing, and output a corresponding DC sampling voltage;

[0070] A voltage stabilizing circuit 320, connected in series between the output terminal of the sampling circuit 310 and the controller. The voltage stabilizing circuit 320 is used to perform voltage stabilizing processing on the DC sampling voltage and output it as a detection voltage waveform.

[0071] Since the pins of the controller 100 can only recognize DC levels with relatively low voltages, in this embodiment, a sampling circuit 310 and a voltage stabilizing circuit 320 are provided. When the overvoltage breaks down the varistor, the sampling circuit 310 samples the AC current flowing through the varistor, and after voltage conversion processing, it performs half-wave rectification processing and outputs Figure 9 the DC sampling voltage shown. In order to make the DC sampling voltage match the pin voltage of the controller 100, the voltage stabilizing circuit 320 further steps down and stabilizes the DC sampling voltage and outputs Figure 10 the detected voltage waveform shown, taking Figure 10 the voltage value in it as an example. Each 5.6V square wave represents the detected voltage waveform in one power frequency cycle.

[0072] Referring to Figure 3 and Figure 5 , in one embodiment, the sampling circuit 310 includes:

[0073] An isolation circuit 311, the first end of its primary side is used to connect to the second end of the varistor ZR1, the second end of its primary side is used to connect to the second power supply end of the mains. The isolation circuit 311 is also used to couple the AC current when the AC current flows through the varistor ZR1, and after voltage conversion processing, it outputs the corresponding AC sampling voltage;

[0074] A rectification circuit 312 is connected in series between the secondary side of the isolation circuit 311 and the input end of the voltage stabilizing circuit 320. The rectification circuit 312 is used to rectify the AC sampling voltage and output the corresponding DC sampling voltage.

[0075] In this embodiment, since the mains power supply system is high voltage and the circuit where the controller 100 is located is low voltage, an isolation circuit 311 needs to be provided between the varistor ZR1 and the controller 100 for electrical isolation. Specifically, the isolation circuit 311 includes:

[0076] A current transformer L1, having a first input pin, a second input pin, a first output pin and a second output pin. The first input pin is the first end of the primary side of the isolation circuit 311, the first output pin is the second end of the primary side of the isolation circuit 311, and the second end of the second output pin is grounded;

[0077] A first resistor R1 is connected in parallel between the second input pin and the second output pin of the current transformer L1.

[0078] When the voltage across the varistor ZR1 exceeds its threshold value, a current will flow through the primary coil inside the current transformer L1. After being coupled with the secondary coil inside it, a corresponding low-voltage induced current is generated. The first resistor R1 connected to the secondary coil uses Ohm's law to convert the incoming low-voltage induced current into a low-voltage alternating current voltage with the same frequency as the voltage across the varistor ZR1, that is, as Figure 8 shown in the AC sampling voltage.

[0079] Since the pins of the controller 100 can only recognize DC voltage, a rectifying circuit 312 is also provided to rectify the AC sampling voltage. Specifically, the rectifying circuit 312 includes:

[0080] The first diode D1, whose anode is the input end of the rectifying circuit 312.

[0081] The first diode D1 has a one-way conduction function, so it can perform half-wave rectification on the AC sampling voltage output by the isolation circuit 311 and output a DC sampling voltage as shown in Figure 9 . It should be noted that since the first diode D1 performs half-wave rectification, the positive and negative breakdown voltage waveforms originally generated in one power frequency cycle are rectified into a positive-phase waveform. Therefore, in Figure 9 , the waveform of a DC sampling voltage can represent the breakdown voltage of one power frequency cycle.

[0082] Referring to Figure 2 and Figure 5 , in one embodiment, the voltage stabilizing circuit 320 includes:

[0083] The second resistor R2, whose first end is the input end of the voltage stabilizing circuit 320;

[0084] The third resistor R3, whose first end is connected to the second end of the second resistor R2 and whose second end is grounded.

[0085] The fourth resistor R4 is connected in series between the second end of the second resistor R2 and the controller 100;

[0086] The voltage stabilizing diode TZ1, the cathode of the voltage stabilizing diode TZ1 is connected to the second end of the second resistor R2, and the anode of the voltage stabilizing diode TZ1 is grounded.

[0087] In this embodiment, the second resistor R2 and the third resistor R3 form a voltage dividing network to further step down the DC sampling voltage output by the rectifying circuit 312 to adapt to the pin voltage of the controller 100.

[0088] It can be understood that the alternating current flowing through the varistor ZR1 may be generated by overvoltage of the varistor ZR1 caused by lightning strike. At this time, the voltage value of the DC sampling voltage output by the sampling circuit 310 is relatively high. Therefore, the zener diode TZ1 is used to stabilize the amplitude of the output overvoltage detection waveform, such as 5.6V, to protect the pins of the controller 100 from damage. The fourth resistor R4 is a current limiting protection resistor for the pins of the controller 100.

[0089] Referring to Figure 2 and Figure 5 , in one embodiment, the voltage stabilizing circuit 320 further includes:

[0090] A first capacitor C1, connected in parallel across the two ends of the zener diode TZ1;

[0091] A second capacitor C2, connected in parallel across the two ends of the zener diode TZ1.

[0092] In this embodiment, at least one of the first capacitor C1 and the second capacitor C2 can be an aluminum electrolytic capacitor. The first capacitor C1 and the second capacitor C2 together form a filter network to filter the voltage detection waveform after voltage stabilization by the zener diode TZ1.

[0093] Referring to Figure 1 and Figure 5 , in one embodiment, the switch circuit 200 includes:

[0094] A relay KY1, including contacts and a coil. The first end of the contacts is used to connect to the first power supply terminal, the second end of the contacts is used to connect to the first end of the varistor ZR1, and the first end of the coil is used to connect to a power supply;

[0095] A switching transistor Q1, whose input terminal is connected to the second end of the coil and whose output terminal is grounded;

[0096] A fifth resistor R5, connected in series between the controlled terminal of the switching transistor Q1 and the controller 100;

[0097] A sixth resistor R6, connected in parallel between the controlled terminal of the switching transistor Q1 and the output terminal of the switching transistor Q1;

[0098] A second diode D2, connected in parallel across the two ends of the coil.

[0099] In this embodiment, the switching transistor Q1 can be a MOS transistor, a triode, etc.

[0100] Taking the switching transistor Q1 as an NPN-type triode as an example for illustration:

[0101] When the varistor ZR1 protection circuit is powered on for the first time, the controller 100 outputs a high-level control signal to the controlled end of the switching transistor Q1, turns on the current loop in which the coil of the relay KY1 is located, controls its contacts to close, and enables the varistor ZR1 to work properly.

[0102] When the overvoltage detected by the controller 100 based on the detected voltage waveform received within a preset period is a power frequency voltage, it outputs a low level to the controlled end of the switching transistor Q1, disconnects the current loop in which the coil of the relay KY1 is located, controls its contacts to bounce back, and disconnects the varistor ZR1 from the first power supply terminal; if the detected voltage waveform is not continuously detected within the preset period, the controller 100 maintains a high-level output, controls the coil to continuously close the contacts, and keeps the varistor ZR1 connected to the first power supply terminal.

[0103] Wherein, the second diode D2 is used to consume the residual current flowing through the coil when the current loop in which the coil of the relay KY1 is located is disconnected.

[0104] Refer to Figure 4 and Figure 5 , in an embodiment, the varistor ZR1 protection circuit further includes:

[0105] A fuse 400, the first end of the fuse 400 is used to connect to the first power supply terminal, the second end of the fuse 400 is used to connect to the input end of the switching circuit 200, and is also used to disconnect the connection between the first power supply terminal and the varistor ZR1 when the maximum current value of the alternating current flowing through the varistor ZR1 reaches the protection current value of the fuse 400.

[0106] In this embodiment, a fuse 400 is connected in series on the loop of the varistor ZR1. At this time, when the varistor ZR1 is broken down and the current causing the varistor ZR1 to short-circuit reaches the protection current value of the fuse 400, the entire circuit is disconnected.

[0107] The present invention also provides an air conditioner, which includes a varistor ZR1 and a varistor ZR1 protection circuit. The specific structure of the varistor ZR1 protection circuit refers to the above embodiments. Since this air conditioner adopts all the technical solutions of the above embodiments, it has at least all the beneficial effects brought by the technical solutions of the above embodiments, which will not be elaborated here one by one.

[0108] The above are only alternative embodiments of the present utility model, and do not limit the patent scope of the present utility model accordingly. Any equivalent structural transformation made by using the content of the specification and drawings of the present utility model under the inventive concept of the present utility model, or any direct / indirect application in other related technical fields shall be included within the patent protection scope of the present utility model.

Claims

1. A varistor protection circuit, characterized in that: include: Controller; A switch circuit, wherein a first connection end thereof is used to connect to a first power supply end of a mains power supply, a second connection end thereof is used to connect to a first end of a varistor, and a controlled end thereof is electrically connected to the controller, and the switch circuit is further used to connect or disconnect the first power supply end and the varistor under the control of the controller; An overvoltage detection circuit is connected in series between the second end of the varistor and the second power supply end of the mains, and its controlled end is electrically connected to the controller. The overvoltage detection circuit is used to sample the AC current flowing through the varistor when the varistor breaks down due to overvoltage, and convert it into a corresponding detection voltage waveform; The controller is also used to control the switch circuit to disconnect the varistor from the first power supply terminal when the detection voltage waveform with a preset voltage value is continuously received within a preset time period.

2. The varistor protection circuit according to claim 1, characterized in that: The overvoltage detection circuit comprises: A sampling circuit, wherein a first sampling terminal is connected to the second terminal of the varistor, and a second sampling terminal is connected to the second power supply terminal, and the sampling circuit is used to sample the AC current flowing through the varistor, perform voltage conversion and rectification processing, and output a corresponding DC sampling voltage; The voltage stabilizing circuit is connected in series between the output end of the sampling circuit and the controller, and is used for stabilizing the DC sampling voltage and outputting it as a detection voltage waveform.

3. The varistor protection circuit according to claim 2, characterized in that: The sampling circuit comprises: An isolation circuit, wherein the first end of the primary side is used to connect to the second end of the varistor, and the second end of the primary side is used to connect to the second power supply end of the mains, and the isolation circuit is also used to couple the alternating current and then perform voltage conversion to output a corresponding alternating current sampling voltage when the alternating current flows through the varistor; The rectifier circuit is connected in series between the secondary side of the isolation circuit and the input end of the voltage stabilizing circuit, and is used for outputting a corresponding DC sampling voltage after rectifying the AC sampling voltage.

4. The varistor protection circuit according to claim 3, characterized in that: The isolation circuit comprises: A current transformer, comprising a first input pin, a second input pin, a first output pin and a second output pin, wherein the first input pin is a first end of the primary side of the isolation circuit, the first output pin is a second end of the primary side of the isolation circuit, and the second end of the second output pin is grounded; The first resistor is connected in parallel to the second input pin and the second output pin of the current transformer.

5. The varistor protection circuit according to claim 3, characterized in that: The rectifier circuit comprises: The first diode has an anode which is the input end of the rectifier circuit and a cathode which is the output end of the rectifier circuit.

6. The varistor protection circuit according to claim 2, characterized in that: The voltage stabilizing circuit comprises: a second resistor, a first end of which is an input end of the voltage stabilizing circuit; a third resistor, a first end of which is connected to the second end of the second resistor, and a second end of which is grounded; a fourth resistor, connected in series between the second end of the second resistor and the controller; A voltage regulator tube, wherein a cathode of the voltage regulator tube is connected to the second end of the second resistor, and an anode of the voltage regulator tube is grounded.

7. The varistor protection circuit according to claim 6, characterized in that: The voltage stabilizing circuit further comprises: A first capacitor is connected in parallel to both ends of the voltage regulator tube; The second capacitor is connected in parallel to the two ends of the voltage regulator tube.

8. The varistor protection circuit according to claim 1, characterized in that: The switch circuit comprises: A relay, comprising a contact and a coil, wherein the first end of the contact is used to connect to the first power supply end, the second end of the contact is used to connect to the first end of the varistor, and the first end of the coil is used to connect to the power supply; A switch tube, whose input end is connected to the second end of the coil and whose output end is grounded; A fifth resistor is connected in series between the controlled end of the switch tube and the controller; a sixth resistor connected in parallel to the controlled end of the switch tube and the output end of the switch tube; The second diode is connected in parallel to both ends of the coil.

9. The varistor protection circuit according to claim 1, characterized in that: The varistor protection circuit also includes: A fuse, wherein the first end of the fuse is used to be connected to the first power supply end, the second end of the fuse is used to be connected to the input end of the switching circuit, and is also used to disconnect the connection between the first power supply end and the varistor when the maximum current value of the alternating current flowing through the varistor reaches the protection current value of the fuse.

10. An air conditioner, characterized in that: It comprises a varistor and a varistor protection circuit as described in any one of claims 1 to 9, wherein the varistor is electrically connected to the varistor protection circuit.

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