Over-temperature protection circuits and electrical appliances

Abstract

The present invention proposes an over-temperature protection circuit and an electrical appliance, wherein the over-temperature protection circuit includes: a load, a working power supply for supplying power to the load, a switching unit for switching the on / off state of the load and the working power supply, and a control power supply for supplying power to the switching unit, and further includes: a protection circuit arranged between the switching unit and the control power supply; when the temperature of the load is higher than a preset over-temperature protection point, the protection circuit cuts off the switching unit so that the switching unit turns off the load; when the temperature of the load is lower than a preset over-temperature protection point, the protection circuit turns on the switching unit so that the switching unit turns on the load. Compared with the prior art, the present invention can turn off the load when the load is over-temperature, thereby playing an over-temperature protection function, and can also turn on the load again when the load returns to normal temperature, thereby allowing the electrical appliance to operate.

Description

Technical Field

[0001] The invention belongs to the field of electrical appliances, in particular to an over-temperature protection circuit and an electrical appliance. Background Art

[0002] With the improvement of living standards, there are more and more electronic products in the home, and the safety level of household appliances is also getting higher and higher. For example, heating loads such as auxiliary heating may cause overheating due to improper use. If the load works under overtemperature conditions for a long time, the load will also be damaged. In the prior art, fuses are usually connected in series for protection. When the temperature reaches a certain value, the fuse can melt and turn off the load. However, when the fuse method is used, when the temperature of the load returns to normal, due to the problem of fuse melting, the circuit cannot be restored to the working state and needs to be repaired before it can be used again.

[0003] Therefore, how to design an over-temperature protection circuit and electrical appliance that can disconnect the load when over-temperature occurs and can turn the load back on when the load returns to normal temperature is a technical problem that needs to be solved urgently in the industry. Summary of the invention

[0004] In view of the problem in the prior art that the load cannot resume working when the load temperature returns to normal, the present invention provides an over-temperature protection circuit and an electrical appliance.

[0005] The technical solution of the present invention is to propose an over-temperature protection circuit, comprising: a load, a working power supply for supplying power to the load, a switching unit for switching the on-off state of the load and the working power supply, and a control power supply for supplying power to the switching unit, and also comprising: a protection circuit arranged between the switching unit and the control power supply;

[0006] When the temperature of the load is higher than a preset over-temperature protection point, the protection circuit cuts off the switching unit, so that the switching unit turns off the load;

[0007] When the temperature of the load is lower than a preset over-temperature protection point, the protection circuit turns on the switching unit, so that the switching unit turns on the load.

[0008] Further, the protection circuit includes a first switch connected in series between the control power supply and the switching unit, and a second switch controlling the on-off state of the first switch;

[0009] When the second switch is turned on, the first switch is turned on, and then the switching unit is turned on, thereby turning on the load;

[0010] When the second switch is turned off, the first switch is turned off, thereby cutting off the switching unit, thereby turning off the load.

[0011] Furthermore, the protection circuit further includes:

[0012] Over-temperature detection unit: used to monitor whether the temperature of the load is higher than the over-temperature protection point;

[0013] An over-temperature switching unit: connected to the over-temperature detection unit and the second switching switch, and when the over-temperature detection unit detects that the temperature of the load is higher than the over-temperature protection point, the second switching switch is cut off; when the over-temperature detection unit detects that the temperature of the load is lower than the over-temperature protection point, the second switching switch is turned on.

[0014] Further, the over-temperature switching unit includes a first over-temperature switching switch connected to the over-temperature detection unit, and a second over-temperature switching switch connecting the first over-temperature switching switch and the second switching switch;

[0015] When the over-temperature detection unit detects that the temperature of the load is higher than the over-temperature protection point, the first over-temperature switch is turned on, and then the second over-temperature switch is turned on, so that the second switch is turned off;

[0016] When the over-temperature detection unit detects that the temperature of the load is lower than the over-temperature protection point, the first over-temperature switch is disconnected, and then the second over-temperature switch is disconnected, thereby turning on the second switch.

[0017] Further, the over-temperature detection unit includes a thermistor RX and a resistor R1 connected in series between the control power supply and the ground, and the over-temperature switching unit is connected between the thermistor RX and the resistor R1;

[0018] When the temperature of the load reaches the over-temperature protection point, the resistance of the thermistor RX reaches a preset resistance, and the over-temperature detection unit sends an over-temperature signal, thereby turning on the first over-temperature switch;

[0019] When the temperature of the load is lower than the over-temperature protection point, the resistance of the thermistor RX is lower than a preset resistance, and the over-temperature detection unit sends a normal temperature signal, thereby turning off the first over-temperature switch.

[0020] Further, the over-temperature switching unit includes a transistor Q3 and a transistor Q4;

[0021] The emitter of the transistor Q3 is connected to the reference voltage, the base is connected to the over-temperature detection unit, the collector is connected to the base of the transistor Q4, the collector of the transistor Q4 is connected to the second switch, and the emitter is grounded;

[0022] The base of the transistor Q3 is turned on when receiving an over-temperature signal, and is turned off when receiving a normal-temperature signal.

[0023] Furthermore, the second switch includes a transistor Q2, the collector of the transistor Q2 is connected to the first switch, the base is connected to a high-level control signal for controlling the operation of the load, and the emitter is grounded.

[0024] Furthermore, the first switch includes a transistor Q1 , the emitter of the transistor Q1 is connected to the control power supply, the collector is connected to the switching unit, and the base is connected to the collector of the transistor Q2 .

[0025] Furthermore, the switching unit is a relay.

[0026] The present invention also provides an electrical appliance, which adopts the over-temperature protection circuit.

[0027] Compared with the prior art, the present invention has at least the following beneficial effects:

[0028] 1. By setting the over-temperature protection circuit, when the temperature of the load is higher than the preset over-temperature protection point, the load is disconnected in time to provide over-temperature protection.

[0029] 2. Over-temperature is detected by connecting a thermistor in series with a resistor. The over-temperature protection point can be adjusted by changing the resistance value of the resistor in series with the thermistor, so that the over-temperature protection point of the over-temperature protection circuit can be adjusted according to the actual needs of the appliance, which is more applicable.

[0030] 3. Switching control is performed by cooperating with thermistors and transistors. The load can be disconnected when the load temperature is higher than the over-temperature protection point to provide over-temperature protection. The load can also be turned on again when the load temperature returns to normal to keep the appliance running, thus avoiding the need for maintenance after over-temperature protection and reducing maintenance costs to a certain extent. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0032] Figure 1 FIG. 4 is a circuit diagram of an embodiment of the present invention. DETAILED DESCRIPTION

[0033] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0034] Thus, a feature indicated in this specification will be used to illustrate one of the features of an embodiment of the present invention, rather than implying that each embodiment of the present invention must have the described feature. In addition, it should be noted that this specification describes many features. Although some features can be combined together to illustrate possible system designs, these features can also be used in other combinations that are not explicitly described. Thus, unless otherwise stated, the described combinations are not intended to be limiting.

[0035] The principle and structure of the present invention are described in detail below with reference to the accompanying drawings and embodiments.

[0036] With the increasing number of electronic products, the safety of electrical appliances is becoming more and more important. However, heating loads such as auxiliary heating often overheat due to improper use, which can easily damage the load. The existing over-temperature protection is through a series fuse. When the load temperature returns to normal, the load cannot work again because the fuse is blown. It needs to be repaired before it can be re-operated, which increases the subsequent repair time and cost. The idea of ​​the present invention is to provide an over-temperature signal to the transistor by connecting a thermistor in series with a resistor, so that it can be turned on when the load is over-temperature, thereby playing an over-temperature protection role, and disconnect at normal temperature to resume work.

[0037] Specifically, the over-temperature protection circuit proposed in the present invention includes a load, a working power supply for supplying power to the load, a switching unit for switching the on / off state of the load and the working power supply, and a control power supply for supplying power to the switching unit, and also includes a protection circuit arranged between the control power supply and the switching unit. The protection circuit is used for over-temperature protection. Since it is connected between the control power supply and the switching unit, it can adjust the on / off state of the switching unit by controlling its own on / off state, wherein when the temperature of the load is higher than a preset over-temperature protection point, the protection circuit cuts off the switching unit, and conversely, when the temperature of the load is lower than the preset over-temperature protection point, the protection circuit turns on the switching unit, and further controls the operating state of the load by the on / off state of the switching unit.

[0038] Preferably, the switching unit adopts a relay, and the relay includes a working circuit part and a switch part. The working circuit part is connected to the control power supply, and the switch part is connected in series with the load. When the relay is powered on, the electromagnet in the relay can attract the switch part to close it, thereby turning on the load and making the load work. On the contrary, when the relay is powered off, the electromagnet in the relay can no longer attract the switch, and the switch part will be disconnected, thereby disconnecting the load to play a protective role. In the present invention, the protection circuit is arranged between the relay and its control power supply. When the temperature of the load reaches the over-temperature protection point, the power supply of the relay can be cut off in time, thereby disconnecting the switch part of the relay to play an over-temperature protection role.

[0039] Compared with other switching devices, the control logic of the relay is simple and the cost is relatively low. In some other embodiments of the present invention, the same control effect can be achieved by adopting other control elements. It is only necessary to satisfy that the switching switch is closed when the power is on to make the load work; and is opened when the power is off, thereby shutting off the load and playing a protective role.

[0040] Furthermore, the protection circuit includes a first switch connected in series between the switching unit and the control power supply, and a second switch that controls the on / off state of the first switch. The first switch is connected in series between the control power supply and the switching unit. When the first switch is disconnected, the control power supply and the switching unit are disconnected, so that the control power supply disconnects the power supply to the switching unit, and the switching unit is disconnected, thereby turning off the load.

[0041] The second switching switch is used to control the on / off state of the first switching switch. When the second switching switch is turned on, it can turn on the first switching switch, thereby closing the switching unit and controlling the load to work; conversely, when the second switching unit is disconnected, it can disconnect the first switching switch, thereby causing the switching unit to control the load to shut down, thereby playing a protective role.

[0042] Furthermore, in order to realize the over-temperature protection function of the present invention, the protection circuit is also provided with an over-temperature detection unit, and an over-temperature switching unit connecting the over-temperature detection unit and the second switching switch. The over-temperature detection unit is used to detect whether the temperature of the load reaches the over-temperature protection point, and when the temperature of the load reaches the over-temperature protection point, an over-temperature signal is sent to the over-temperature switching unit, so that the over-temperature switching unit turns off the second switching switch, and then turns off the load, thereby playing an over-temperature protection role. At the same time, when the temperature of the load does not reach the over-temperature protection point, the over-temperature detection unit sends a normal temperature signal to the over-temperature switching unit, so that the over-temperature switching unit turns on the second switching switch, so that the load works.

[0043] Among them, the over-temperature detection unit can be a device for detecting temperature, such as a temperature detector, so that it can send an over-temperature signal to the over-temperature switching unit when the temperature is over-temperature. The over-temperature switching unit adopts a corresponding switching device so that when it receives an over-temperature fault, it turns off the second switching switch, thereby disconnecting the load to provide over-temperature protection.

[0044] See also Figure 1 In a preferred embodiment of the present invention, the over-temperature detection unit uses a thermistor RX and a resistor R1 connected in series between the control power supply and the ground. The characteristic of the thermistor is that the resistance changes with the change of temperature. Since the thermistor RX is connected in series with the resistor R1, when the resistance of the thermistor RX changes, its own voltage division will also change. The over-temperature switching unit is connected between the thermistor RX and the resistor R1, receives the voltage between the thermistor RX and the resistor R1, and uses the voltage when the over-temperature protection is reached as an over-temperature signal to control the on-off of the second switching switch. For example, when the temperature is 70 degrees, the resistance of the thermistor RX is a at 70 degrees. At this time, through the voltage division of the thermistor RX, the voltage received by the over-temperature switching unit is A, that is, A is the over-temperature signal. At this time, the temperature of 70 degrees is the over-temperature protection point set by the over-temperature protection circuit. When the temperature in the load is greater than or equal to 70 degrees, it is determined that the load is over-temperature and the load is turned off, thereby playing a protective role. Among them, when the temperature of the load does not reach 70 degrees, the voltage received by the over-temperature switching unit is B, which is used as a normal temperature signal. In this case, it is not enough to guide the over-temperature switching unit, and the load works normally.

[0045] It should be noted that in this embodiment, the over-temperature protection point is adjustable by adopting the mode of connecting thermistor RX and resistor R1 in series. The over-temperature protection point is the set protection temperature. When it is higher than the over-temperature protection point, it is determined that the load has an over-temperature problem. In this embodiment, by changing the size of resistor R1, the size of the over-temperature protection point can be adjusted. For example, when the resistance value of resistor R1 is n1, the over-temperature signal is voltage A at this time. When the resistance value of thermistor RX reaches m1, the voltage divided by it and resistor R1 reaches A. At this time, the temperature of thermistor RX is Q1, that is, the over-temperature protection point is Q1 temperature at this time; when the size of resistor R1 is changed to n2, due to the change of the size of resistor R1, when the over-temperature switching unit receives voltage A, the resistance value of thermistor RX will also be changed to m2 at this time, and its corresponding temperature is also different from before. It is assumed that the temperature of thermistor RX is Q2 at this time, that is, the over-temperature protection point is Q2 temperature at this time. Through the adjustment of resistor R1, the size of the over-temperature protection point can be adaptively adjusted according to the needs of different electrical appliances, so that the applicability of the present invention is better. Among them, after determining the voltage of the over-temperature signal, it is only necessary to obtain the law of temperature and resistance change according to the model of the thermistor RX, and then set the size of the resistor R1 according to the circuit voltage division principle to determine the specific over-temperature protection point.

[0046] Furthermore, the over-temperature protection unit includes a first over-temperature switching switch connected to the over-temperature detection unit, and a second over-temperature switching switch connecting the first over-temperature switching switch and the second switching switch. The setting method is that when the first over-temperature switching switch receives an over-temperature signal, it is turned on, and then the second over-temperature switching switch is turned on. After the second switching switch is turned on, it can pull down the signal output to the second switching switch, and then turn off the second switching switch, thereby disconnecting the load.

[0047] See also Figure 1 Specifically, the over-temperature switching switch includes a transistor Q3 and a transistor Q4, wherein the emitter of the transistor Q3 is connected to a reference voltage, and the base is connected between the thermistor RX and the resistor R1, for receiving an over-temperature signal, the collector of the transistor Q3 is connected to the base of the transistor Q4, the collector of the transistor Q4 is connected to the second switching switch, and the emitter is grounded.

[0048] It can be seen from the above settings that when the load is over-temperature, the voltage between the thermistor RX and the resistor R1 reaches A, which will output an over-temperature signal to the base of the transistor Q3, thereby controlling the transistor Q3 to be turned on, and then turning on the transistor Q4, so that the level at the second switch is pulled down, the load is turned off, and the over-temperature protection function is played. In this embodiment, the transistor Q3 and the transistor Q4 are used to control the second switch because the conduction characteristics of the transistor can be turned on as long as the voltage reaches. After the setting of the transistor, when the load is over-temperature, the load can be disconnected to play a protective role. At the same time, when the load is disconnected, the temperature in the load decreases, and the voltage division of the thermistor RX also changes accordingly. When the temperature in the load is lower than the over-temperature protection point, the voltage division of the thermistor RX is not enough to turn on the transistor Q3. At this time, the transistor Q3 will be turned off again, so that the transistor Q4 is turned off, and then the transistor Q2 is turned on again, and the load resumes work. If other control methods are used, such as a fuse blowing method, when the over-temperature point is reached for the first time, the fuse blows, thereby shutting off the load. When the temperature returns to normal, the fuse cannot be turned on again, so that it cannot resume working and needs to be repaired before it can resume working. In the present invention, the combination of the transistor Q3, the transistor Q4 and the thermistor RX can achieve a self-recovery effect, the circuit can be reused, and the practicality is higher.

[0049] It should be noted that the thermistor RX in the present invention adopts a PTC resistor (positive temperature coefficient resistor), and the resistance value of the resistor increases with the increase of temperature, that is, when the temperature increases, the divided voltage of the thermistor RX will become higher, and the voltage output to the base of the transistor Q3 will decrease. When it is lower than the emitter voltage, the transistor Q3 is turned on; when the temperature decreases, the resistance value of the thermistor RX decreases, the divided voltage of the thermistor RX decreases, and the voltage output to the base of the transistor Q3 increases. When it is higher than the emitter voltage, the transistor Q3 is turned off.

[0050] It should be pointed out that when the temperature of the load reaches the over-temperature protection point, the voltage at the base of transistor Q3 is A, and the over-temperature signal is only less than the voltage signal of A voltage. Since the resistance of the PTC resistor increases with the increase of temperature, that is, the higher the temperature, the lower the voltage output to the base of transistor Q3, that is, when the temperature of the load is greater than or equal to the over-temperature protection point, the voltage output to the base of transistor Q3 is less than or equal to A. This part of the voltage is used as an over-temperature signal and can be used to turn on transistor Q3 and then turn off the load. Correspondingly, the normal temperature signal refers to a voltage signal higher than A voltage, and this part of the voltage can disconnect transistor Q3 and turn on the load. Among them, the thermistor RX is set at the load so that it can better sense temperature changes and achieve better control effects.

[0051] Further, the reference voltage is provided by resistors R2 and R3, and resistors R2 and R3 are connected in series between the control power supply and the emitter of transistor Q3 to provide a reference voltage to the emitter of transistor Q3. It should be noted that the conduction condition of transistor Q3 is that it is turned on when the voltage is lower than the reference voltage, and the change rule of the thermistor is that the resistance increases with the increase of temperature. As the temperature of the load increases, the resistance of the thermistor gradually increases, thereby reducing the voltage output to the base of transistor Q3, and then turning on transistor Q3. In the present invention, the way to change the over-temperature protection point can also be achieved by changing the size of resistors R2 and R3. By changing the size of resistors R2 and R3, the reference voltage changes, that is, the voltage required when transistor Q3 is turned on changes. When the resistance value of resistor R1 remains unchanged, the resistance value of the thermistor RX is different from before when transistor Q3 is turned on, that is, the temperature when the over-temperature signal is sent is different, and the corresponding over-temperature protection point also changes accordingly. The specific setting method can be designed according to the thermistor and the circuit voltage division principle, which will not be repeated here. It should be noted that, although the size of the over-temperature protection point can be changed by changing the resistance value of resistor R1, the reference voltage needs to be considered when adjusting the over-temperature protection point by changing the resistance value of resistor R1. It must be ensured that when the over-temperature protection point is reached, the voltage output to the base of transistor Q3 is lower than the reference voltage. By adjusting the reference voltage by changing resistors R2 and R3, there is no need to consider the setting of resistor R1, and the method of setting the over-temperature protection point is simpler.

[0052] For further information, see Figure 1 The second switch is a transistor Q2, the collector of which is connected to the first switch, the base of which is connected to a high-level control signal for controlling the operation of the load, and the emitter of which is grounded. A resistor is connected in series at the base of the transistor Q2 and then connected to a level signal, which is used to play a role in voltage division and current limiting. When the transistor Q4 is turned on, the high-level control signal will be directly guided to the ground through the transistor Q4, so that the voltage at the base of the transistor Q2 is 0, and the transistor Q2 is turned off, thereby cutting off the first switch.

[0053] The first switch is a transistor Q1, the emitter of the transistor Q1 is connected to the control power supply, the collector is connected to the switching unit, and the base is connected to the collector of the transistor Q2. Figure 1 It can be clearly seen from the setting of transistor Q1 that when transistor Q1 is turned off, it is equivalent to an open circuit, and the control unit will not be able to provide voltage to the switching unit. At this time, the switching unit is powered off and the load will be controlled to be turned off. Through the setting of transistor Q1, the over-temperature protection circuit can control the on and off of the switching unit, and then control the state of the load.

[0054] According to the idea of ​​the present invention, MOS tubes and other switching tube devices can be used instead of triodes, which can also achieve the same technical effect. Compared with MOS tubes, triodes have lower costs, simpler connections, and higher practicality.

[0055] The control process of the present invention is:

[0056] When the appliance starts working, a high-level control signal is sent to the base of transistor Q2, transistor Q2 is turned on, and then transistor Q1 is turned on, the control power supply is supplied to the switching unit, and the load works normally. In this case, since the temperature is lower than the over-temperature protection point, the resistance of the thermistor RX is small, the base voltage of transistor Q3 is higher than the reference voltage, and transistor Q3 is turned off without entering the over-temperature protection;

[0057] When the load is overheated, since the temperature in the load reaches the over-temperature protection point, the resistance of the thermistor RX increases, so that the voltage output to the base of the transistor Q3 reaches the first reference voltage, the transistor Q3 is turned on, and enters the over-temperature protection. At this time, the transistor Q4 is turned on, and the high-level control signal is directly introduced into the ground through the transistor Q4, so that the transistor Q2 is turned off, and then the transistor Q1 is turned off. The control power supply cannot supply power to the switching unit, and the load is disconnected to play an over-temperature protection role;

[0058] After the over-temperature protection, the temperature in the load gradually decreases. When it is lower than the over-temperature protection point, the resistance of the thermistor RX decreases due to the decrease in temperature, and the voltage output to the base of the transistor Q3 increases, causing the transistor Q3 to be disconnected again, and then the transistor Q4 is disconnected. Since the transistor Q4 is disconnected, the high-level control signal is normally input to the base of the transistor Q2, and the transistor Q2 is turned on, and then the transistor Q1 is turned on. The control power supply starts to supply power to the switching unit, and the switching unit turns on the load again, so that the circuit load resumes work.

[0059] The present invention further provides an electrical appliance, which comprises a load and an over-temperature protection circuit connected to the load, wherein the over-temperature protection circuit adopts the above-mentioned over-temperature protection circuit.

[0060] Compared with the prior art, the over-temperature protection circuit of the present invention can shut down the load in time when the load is over-temperature, so that the load stops working and avoids damage to the electrical appliance. At the same time, the present invention can also adjust the over-temperature protection point by adjusting the resistor R1 or the resistor R2 and the resistor R3, so that it can adapt to different electrical appliance requirements and settings, and has better applicability. Furthermore, the over-temperature protection circuit of the present invention can not only shut down the load when the temperature is over-temperature to provide over-temperature protection, but also shut down the transistor Q3 and the transistor Q4 when the temperature drops, and then turn on the transistor Q2 and the transistor Q1, so that the switching unit is powered on again and the load resumes working. The circuit has a self-recovery function, which avoids the problem of needing to be repaired before being reused after a fault, and reduces maintenance costs.

[0061] The above embodiments are only used to illustrate the specific implementation of the present invention. It should be noted that, for those skilled in the art, several modifications and changes can be made without departing from the concept of the present invention, and these modifications and changes should all fall within the protection scope of the present invention.

Claims

1. Over-temperature protection circuit, including: A load, a working power supply for supplying power to the load, a switching unit for switching the on / off state of the load and the working power supply, and a control power supply for supplying power to the switching unit, characterized in that it also includes: a protection circuit arranged between the switching unit and the control power supply; When the temperature of the load is higher than a preset over-temperature protection point, the protection circuit cuts off the switching unit, so that the switching unit turns off the load; When the temperature of the load is lower than a preset over-temperature protection point, the protection circuit turns on the switching unit so that the switching unit turns on the load; The protection circuit includes a first switch connected in series between the control power supply and the switching unit, and a second switch controlling the on-off state of the first switch; When the second switch is turned on, the first switch is turned on, thereby turning on the switching unit. element, thereby turning on the load; When the second switch is disconnected, the first switch is disconnected, thereby cutting off the switching unit, thereby turning off the load; The protection circuit further comprises: Over-temperature detection unit: used to monitor whether the temperature of the load is higher than the over-temperature protection point; Over-temperature switching unit: connected to the over-temperature detection unit and the second switching switch. When the detection unit detects that the temperature of the load is higher than the over-temperature protection point, the second switching switch is cut off; when the over-temperature detection unit detects that the temperature of the load is lower than the over-temperature protection point, the second switching switch is turned on.

2. The over-temperature protection circuit according to claim 1, characterized in that: The over-temperature switching unit includes a first over-temperature switching switch connected to the over-temperature detection unit, and a second over-temperature switching switch connecting the first over-temperature switching switch and the second switching switch; When the over-temperature detection unit detects that the temperature of the load is higher than the over-temperature protection point, the first The first over-temperature switch is turned on, thereby turning on the second over-temperature switch, thereby turning off the second switch; When the over-temperature detection unit detects that the temperature of the load is lower than the over-temperature protection point, the first over-temperature switch is disconnected, and then the second over-temperature switch is disconnected, thereby turning on the second switch.

3. The over-temperature protection circuit according to claim 2, characterized in that: The over-temperature detection unit includes a thermistor RX and a resistor R1 connected in series between the control power supply and the ground, and the over-temperature switching unit is connected between the thermistor RX and the resistor R1; When the temperature of the load reaches the over-temperature protection point, the resistance of the thermistor RX reaches the preset value. The over-temperature detection unit sends an over-temperature signal, thereby turning on the first over-temperature switch; When the temperature of the load is lower than the over-temperature protection point, the resistance of the thermistor RX is lower than a preset resistance, and the over-temperature detection unit sends a normal temperature signal, thereby turning off the first over-temperature switch.

4. The over-temperature protection circuit according to claim 1, characterized in that: The over-temperature switching unit includes a transistor Q3 and a transistor Q4; The emitter of the transistor Q3 is connected to the reference voltage, the base is connected to the over-temperature detection unit, and the collector The electrode is connected to the base of the transistor Q4, the collector of the transistor Q4 is connected to the second switch, and the emitter is grounded; The base of the transistor Q3 is turned on when receiving an over-temperature signal, and is turned off when receiving a normal-temperature signal.

5. The over-temperature protection circuit according to claim 4, characterized in that: The second switch includes a transistor Q2 , the collector of the transistor Q2 is connected to the first switch, the base is connected to a high-level control signal for controlling the operation of the load, and the emitter is grounded.

6. The over-temperature protection circuit according to claim 5, characterized in that: The first switch includes a transistor Q1 , wherein the emitter of the transistor Q1 is connected to the control power supply, the collector is connected to the switching unit, and the base is connected to the collector of the transistor Q2 .

7. The over-temperature protection circuit according to claim 1, characterized in that: The switching unit is a relay.

8. An electrical appliance, characterized in that The electrical appliance adopts the over-temperature protection circuit as described in any one of claims 1 to 7.

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