Heater protection circuit and heater

Abstract

The application discloses a kind of heater protection circuit and heater, including temperature detection unit, comparison unit and processor unit, temperature detection unit is exported with the temperature corresponding voltage signal of heat generator to comparison unit, comparison unit compares voltage signal with voltage upper limit value and voltage lower limit value, in the case where voltage signal is greater than voltage upper limit value or voltage signal is less than voltage lower limit value, comparison unit exports low level temperature enable signal to pulse width modulation controller in processor unit, to make pulse width modulation controller stop output pulse width modulation signal, disconnect the power switch of heat generator, to realize the power switch of heat generator is disconnected quickly in the case where the temperature of heat generator appears abnormal, reliable heat protection is realized to heater, since it is not necessary to set mechanical thermal fuse in circuit, while improving the response speed of heat protection, reduce the volume of heater and reduce cost, especially suitable for small portable heater.

Description

Technical Field

[0001] This application relates to the field of protection circuit technology, and in particular to a heater protection circuit and a heater. Background Technology

[0002] A heater is an electrical appliance that uses electrical energy to achieve a heating effect, converting electrical energy into heat energy. Examples include some household appliances such as hair curlers, hair straighteners, and hair dryers. During use, the heating element in a heater may overheat. Therefore, heaters typically include a protection circuit to prevent heating element failure and ensure the heater's safety.

[0003] Currently, heating element failure protection generally relies on the heating element's resistance increasing (positive temperature coefficient) as it heats up, thus reducing the heating current for self-protection, or it uses an external mechanical thermal fuse. However, with the reduced heating current method, the heating element cannot be completely disconnected from the power supply during overheating, failing to achieve true thermal protection. External mechanical thermal fuses are bulky and slow to respond, making them unsuitable for applications with high space and performance requirements, especially for portable heating products. Furthermore, mechanical thermal fuses are expensive, significantly reducing the competitiveness of price-sensitive products.

[0004] For example, patent CN103384419A discloses a self-fuse-protected electric heating device, which includes an electric heater, a fuse, and a temperature limiter. The live wire of the electric heater is connected in series with the fuse and can be connected to the live wire of an external AC power source through the fuse. The neutral wire of the electric heater is connected in series with the temperature limiter and can be connected to the neutral wire of an external AC power source through the temperature limiter. A fusible heating element is installed inside the electric heater. Because it protects the heater through a fuse, the electrical equipment is large and the thermal protection response speed is slow. Utility Model Content

[0005] This application provides a heater protection circuit and a heater, including a temperature detection unit, a comparison unit, and a processor unit, to improve the thermal protection response speed of the heater.

[0006] A first aspect provides a heater protection circuit, comprising: a temperature detection unit for detecting the temperature of a heating element in the heater and outputting a voltage signal corresponding to the temperature; a comparison unit for comparing the voltage signal with an upper voltage limit and a lower voltage limit, and outputting a temperature enable signal corresponding to the comparison result, wherein the temperature enable signal is low when the voltage signal is greater than the upper voltage limit or less than the lower voltage limit; and a processor unit including a pulse width modulation controller, wherein the pulse width modulation controller stops outputting the pulse width modulation signal to disconnect the power switch of the heating element when the temperature enable signal is low; wherein the temperature detection unit is in contact with the heating element, the output terminal of the temperature detection unit is connected to a first terminal of the comparison unit, the second terminal of the comparison unit is connected to the input terminal of the pulse width modulation controller via the first terminal of the processor unit, and the output terminal of the pulse width modulation controller is connected to the power switch as the second terminal of the processor unit.

[0007] In some embodiments, the comparison unit includes a first comparator, a second comparator, and a first resistor. The positive input terminal of the first comparator is connected to the upper voltage limit. The negative input terminal of the first comparator and the positive input terminal of the second comparator are connected to the first terminal of the comparison unit. The negative input terminal of the second comparator is connected to the lower voltage limit. The output terminals of the first comparator, the second comparator, and the first terminal of the first resistor are all connected to the second terminal of the comparison unit. The second terminal of the first resistor is connected to a first power supply. The first comparator and the second comparator employ open-drain output or open-collector output.

[0008] This ensures that the temperature enable signal is reliably low when the voltage signal is greater than the upper voltage limit or less than the lower voltage limit, thus improving the reliability of the comparator unit.

[0009] In some embodiments, the temperature detection unit includes a second resistor and a third resistor. The second resistor is a negative temperature coefficient thermistor. The second resistor is attached to the surface of the heating element. The first end of the second resistor is connected to a second power supply. The second end of the second resistor and the first end of the third resistor are connected to the output terminal of the temperature detection unit. The second end of the third resistor is grounded.

[0010] Since the resistance of the second resistor decreases as the temperature increases, the voltage signal can accurately reflect the actual temperature of the heating element and whether the temperature detection unit is functioning properly, thereby improving the reliability of the temperature detection unit.

[0011] In some embodiments, the temperature detection unit further includes a fourth resistor and a first capacitor. The second end of the second resistor and the first end of the third resistor are connected to the output terminal of the temperature detection unit via the fourth resistor. One end of the first capacitor is connected to the output terminal of the temperature detection unit, and the other end of the first capacitor is grounded.

[0012] The fourth resistor and the first capacitor can filter the voltage signal, thereby further improving the accuracy of the voltage signal.

[0013] In some embodiments, the output of the temperature detection unit is also connected to a third terminal of the processor unit. This improves the reliability of the heater.

[0014] In some embodiments, the processor unit includes an analog-to-digital converter module for converting the voltage signal received at a third terminal of the processor unit into a temperature signal. This improves the reliability of the heater.

[0015] In some embodiments, when the voltage signal is not greater than the upper voltage limit and not less than the lower voltage limit, the temperature enable signal is at a high level, and the pulse width modulation controller is further configured to output a pulse width modulation signal when the temperature enable signal is at a high level. This improves the reliability of the heater.

[0016] In some embodiments, the number of temperature detection units and the number of comparison units are both greater than the number of heating elements, and each temperature detection unit corresponds to one comparison unit.

[0017] By ensuring that the number of temperature detection units and comparison units is greater than the number of heating elements, the heater protection circuit can still perform its thermal protection function normally even if one of the temperature detection units or comparison units malfunctions. This achieves a redundant design for the protection circuit and further improves the reliability of the heater.

[0018] In some embodiments, the temperature detection unit includes a thermocouple and an operational amplifier. The thermocouple is in contact with the heating element, and the output terminal of the thermocouple is connected to the input terminal of the operational amplifier. The output terminal of the operational amplifier is the output terminal of the temperature detection unit. This improves the flexibility of the heater protection circuit.

[0019] In a second aspect, a heater is provided, including a heating element and a heater protection circuit as described in the first aspect.

[0020] By applying the above technical solution, the heater protection circuit includes a temperature detection unit, a comparison unit, and a processor unit. The temperature detection unit outputs a voltage signal corresponding to the temperature of the heating element to the comparison unit. The comparison unit compares the voltage signal with the upper and lower voltage limits. If the voltage signal is greater than the upper voltage limit or less than the lower voltage limit, the comparison unit outputs a low-level temperature enable signal to the pulse width modulation controller in the processor unit. This causes the pulse width modulation controller to stop outputting the pulse width modulation signal and disconnect the power switch of the heating element. This enables the rapid disconnection of the heating element's power switch in case of abnormal temperature, achieving reliable thermal protection for the heater. Since there is no need to install a mechanical thermal fuse in the circuit, the thermal protection response speed is improved, while the size of the heater is reduced and the cost is lowered, making it particularly suitable for small portable heaters. Attached Figure Description

[0021] To more clearly illustrate the technical solutions of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments recorded in this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 This application provides an embodiment of a heater protection circuit. Figure 1 ; Figure 2 This application provides an embodiment of a heater protection circuit. Figure 2 ; Figure 3 This application provides an embodiment of a heater protection circuit. Figure 3 ; Figure 4 This application provides an embodiment of a heater protection circuit. Figure 4 .

[0023] Figures 1-4 In the middle, 10 is the temperature detection unit; 20 is the comparison unit; 30 is the processor unit; 31 is the pulse width modulation controller; 32 is the analog-to-digital conversion module; 40 is the power switch; and 50 is the heating element. Detailed Implementation

[0024] Various embodiments and features of this application are described herein with reference to the accompanying drawings.

[0025] It should be understood that various modifications can be made to the embodiments described herein. Therefore, the above description should not be considered as limiting, but merely as an example of embodiments. Other modifications within the scope and spirit of this application will be apparent to those skilled in the art.

[0026] The accompanying drawings, which are included in and form part of this specification, illustrate embodiments of the present application and, together with the general description of the present application given above and the detailed description of the embodiments given below, serve to explain the principles of the present application.

[0027] These and other features of this application will become apparent from the following description of preferred forms of embodiments given as non-limiting examples, with reference to the accompanying drawings.

[0028] It should also be understood that although this application has been described with reference to some specific examples, those skilled in the art can certainly implement many other equivalent forms of this application.

[0029] The above and other aspects, features and advantages of this application will become more apparent when taken in conjunction with the accompanying drawings and in view of the following detailed description.

[0030] Specific embodiments of this application are described thereafter with reference to the accompanying drawings; however, it should be understood that the claimed embodiments are merely examples of this application, which can be implemented in various ways. Well-known and / or repeated functions and structures are not described in detail to avoid unnecessary or redundant details that could obscure the application. Therefore, the specific structural and functional details claimed herein are not intended to be limiting, but merely serve as the basis and representative basis for the claims to teach those skilled in the art to use this application in a variety of substantially any suitable detailed structures.

[0031] This specification may use the phrases “in one embodiment,” “in another embodiment,” “in yet another embodiment,” or “in other embodiments,” all of which may refer to one or more of the same or different embodiments according to this application.

[0032] An embodiment of this application discloses a heater protection circuit, including a temperature detection unit, a comparison unit, and a processor unit. The temperature detection unit outputs a voltage signal corresponding to the temperature of the heating element to the comparison unit. The comparison unit compares the voltage signal with an upper voltage limit and a lower voltage limit. If the voltage signal is greater than the upper voltage limit or less than the lower voltage limit, the comparison unit outputs a low-level temperature enable signal to the pulse width modulation controller in the processor unit, causing the pulse width modulation controller to stop outputting the pulse width modulation signal and disconnecting the power switch of the heating element. This enables rapid disconnection of the power switch of the heating element in case of abnormal temperature, achieving reliable thermal protection for the heater. Since a mechanical thermal fuse is not required in the circuit, the thermal protection response speed is improved, while the size of the heater is reduced and the cost is lowered, making it particularly suitable for small portable heaters.

[0033] like Figure 1 As shown, the heater protection circuit includes: The temperature detection unit 10 is used to detect the temperature of the heating element 50 in the heater and output a voltage signal corresponding to the temperature. The comparison unit 20 is used to compare the voltage signal with the upper voltage limit and the lower voltage limit respectively, and output the temperature enable signal corresponding to the comparison result. When the voltage signal is greater than the upper voltage limit or less than the lower voltage limit, the temperature enable signal is low level. The processor unit 30 includes a pulse width modulation controller 31, which is used to stop outputting the pulse width modulation signal when the temperature enable signal is low, so as to disconnect the power switch 40 of the heating element 50. The temperature detection unit 10 is in contact with the heating element 50. The output of the temperature detection unit 10 is connected to the first end of the comparison unit 20. The second end of the comparison unit 20 is connected to the input end of the pulse width modulation controller 31 via the first end of the processor unit 30. The output end of the pulse width modulation controller 31 is connected to the power switch 40 as the second end of the processor unit 30.

[0034] In this embodiment, the heater may include, for example, any one of the following: a hair curler, a hair dryer, an electric hand warmer, or a hand and foot warmer. The heater may include one or more heating elements 50 (such as heating wires), which are connected to a power switch 40. When the power switch 40 is turned on, the temperature of the heating element 50 rises. The processor unit 30 may include, for example, a microcontroller unit (MCU). The processor unit 30 is equipped with a pulse width modulation (PWM) controller 31. During normal operation of the heater, the PWM controller 31 in the processor unit 30 controls the power switch 40 by outputting a pulse width modulation signal (PWM signal) to make the heating element 50 reach or maintain the target temperature. The PWM controller 31 has a hardware braking function; when the temperature enable signal is low, it stops outputting the PWM signal to disconnect the power switch 40 of the heating element 50.

[0035] After the heater is started, the temperature detection unit 10 detects the temperature of the heating element 50, converts the temperature into a voltage signal, and outputs the voltage signal to the comparison unit 20. The comparison unit 20 compares the voltage signal with the upper and lower voltage limits respectively, and outputs a temperature enable signal to the pulse width modulation controller 31 in the processor unit 30. If the voltage signal is greater than the upper voltage limit or less than the lower voltage limit, it indicates that the temperature of the heating element 50 is too high or too low, and the temperature enable signal is low. After receiving the low-level temperature enable signal, the pulse width modulation controller 31 stops outputting the pulse width modulation signal and completely disconnects the electrical connection between the power supply and the heating element 50, thereby ensuring that the temperature of the heating element 50 is within the controlled range, realizing the electronic thermal fuse protection function, and thus achieving reliable thermal protection for the heater.

[0036] The heater protection circuit of this application embodiment includes: a temperature detection unit 10, used to detect the temperature of the heating element 50 in the heater and output a voltage signal corresponding to the temperature; a comparison unit 20, used to compare the voltage signal with an upper voltage limit and a lower voltage limit respectively, and output a temperature enable signal corresponding to the comparison result, wherein the temperature enable signal is low level when the voltage signal is greater than the upper voltage limit or less than the lower voltage limit; and a processor unit 30, including a pulse width modulation controller 31, which stops outputting the pulse width modulation signal when the temperature enable signal is low level, thereby disconnecting the power switch 40 of the heating element 50; wherein the temperature detection unit 10 is in contact with the heating element 50, the output terminal of the temperature detection unit 10 is connected to the first terminal of the comparison unit 20, the second terminal of the comparison unit 20 is connected to the input terminal of the pulse width modulation controller 31 via the first terminal of the processor unit 30, and the output terminal of the pulse width modulation controller 31 is connected to the power switch 40 as the second terminal of the processor unit 30. This enables hardware-level temperature anomaly detection. Since there is no need to install a mechanical thermal fuse in the circuit, it improves the thermal protection response speed, reduces the size of the heater, and lowers the cost, making it especially suitable for small portable heaters.

[0037] In some embodiments of this application, such as Figure 2As shown, the comparison unit 20 includes a first comparator U1, a second comparator U2, and a first resistor R1. The positive input terminal of the first comparator U1 is connected to the upper voltage limit value VREF_UP. The negative input terminal of the first comparator U1 and the positive input terminal of the second comparator U2 are connected to the first terminal of the comparison unit 20. The negative input terminal of the second comparator U2 is connected to the lower voltage limit value VREF_DOWN. The output terminals of the first comparator U1, the second comparator U2, and the first terminal of the first resistor R1 are all connected to the second terminal of the comparison unit 20. The second terminal of the first resistor R1 is connected to the first power supply VCC. The first comparator U1 and the second comparator U2 adopt open-drain output or open-collector output.

[0038] In this embodiment, the first comparator U1 compares the voltage signal with the upper voltage limit VREF_UP, and the second comparator U2 compares the voltage signal with the lower voltage limit VREF_DOWN. If the voltage signal is greater than the upper voltage limit VREF_UP, the first comparator U1 outputs a low level, and the second comparator U2 outputs a high level. Since the first comparator U1 and the second comparator U2 use open-drain or open-collector outputs, the outputs of the first comparator U1 and the second comparator U2 form a logical AND relationship, making the temperature enable signal output by the comparison unit 20 low. If the voltage signal is less than the lower voltage limit VREF_DOWN, the second comparator U2 outputs a low level, and the first comparator U1 outputs a high level. Since the first comparator U1 and the second comparator U2 use open-drain or open-collector outputs, the outputs of the first comparator U1 and the second comparator U2 form a logical AND relationship, making the temperature enable signal output by the comparison unit 20 low. Figures 2-4 In this context, VBUS represents the power supply to the heating element.

[0039] Since the first comparator U1 and the second comparator U2 in the comparison unit 20 adopt open-drain output or open-collector output, the output terminals of the first comparator U1 and the second comparator U2 are connected in parallel to form a logical AND relationship, thereby reliably making the temperature enable signal low level when the voltage signal is greater than the upper limit of the voltage or less than the lower limit of the voltage, thus improving the reliability of the comparison unit 20.

[0040] For example, if the upper limit of the temperature of the heating element is +150℃, the corresponding upper limit of the voltage is 4902mV, and the lower limit of the temperature is -20℃, the corresponding lower limit of the voltage is 433mV, then if the voltage signal is greater than 4902mV or less than 433mV, the temperature enable signal is low.

[0041] In some embodiments of this application, such as Figure 2As shown, the temperature detection unit 10 includes a second resistor RT1 and a third resistor R3. The second resistor RT1 is a negative temperature coefficient thermistor. The second resistor RT1 is attached to the surface of the heating element 50. The first end of the second resistor RT1 is connected to the second power supply VREF. The second end of the second resistor RT1 and the first end of the third resistor R3 are connected to the output terminal of the temperature detection unit 10. The second end of the third resistor R3 is grounded.

[0042] In this embodiment, the second resistor RT1 is a negative temperature coefficient thermistor, i.e., an NTC resistor, whose resistance decreases as the temperature increases. The second resistor RT1 can be mounted on the surface of the heating element 50. The first end of the second resistor RT1 is connected to the second power supply VREF, and the second end of the second resistor RT1 is grounded through the third resistor R3. The output terminal of the temperature detection unit 10 is led out from between the first resistor R1 and the second resistor RT1, so that the output terminal of the temperature detection unit 10 outputs a voltage signal. Since the resistance of the second resistor RT1 decreases as the temperature increases, the voltage signal can accurately reflect the actual temperature of the heating element and whether the temperature detection unit 10 is functioning normally, thereby improving the reliability of the temperature detection unit 10.

[0043] For example, if the second power supply VREF is 5000mV, the second resistor RT1 is normal, and the temperature of the heating element exceeds +150℃, the voltage signal will be greater than the upper voltage limit of 4902mV, causing the temperature enable signal to be low. Alternatively, if the second resistor RT1 is normal, and the temperature of the heating element is below -20℃, the voltage signal will be less than the upper voltage limit of 433mV, causing the temperature enable signal to be low. Alternatively, if the second resistor RT1 is short-circuited, the voltage signal can be 5000mV, greater than the upper voltage limit of 4902mV, causing the temperature enable signal to be low. Alternatively, if the second resistor RT1 is open-circuited, the voltage signal can be 0mV, less than the lower voltage limit of 433mV, causing the temperature enable signal to be low.

[0044] In some embodiments of this application, such as Figure 2 As shown, the temperature detection unit 10 also includes a fourth resistor R4 and a first capacitor C1. The second end of the second resistor RT1 and the first end of the third resistor R3 are connected to the output terminal of the temperature detection unit 10 via the fourth resistor R4. One end of the first capacitor C1 is connected to the output terminal of the temperature detection unit 10, and the other end of the first capacitor C1 is grounded.

[0045] In this embodiment, the fourth resistor R4 and the first capacitor C1 can filter the voltage signal, thereby further improving the accuracy of the voltage signal.

[0046] In some embodiments of this application, such as Figure 3 As shown, the output of the temperature detection unit 10 is also connected to the third terminal of the processor unit 30.

[0047] In this embodiment, by connecting the output of the temperature detection unit 10 to the third terminal of the processor unit 30, the processor unit 30 can obtain a voltage signal corresponding to the temperature of the heating element 50. This allows the processor unit 30 to monitor the temperature of the heating element 50 in real time based on the voltage signal and generate a suitable PWM signal. Alternatively, the processor unit 30 can send the temperature of the heating element 50 to the display screen of the heater for display, thereby improving the reliability of the heater.

[0048] In some embodiments of this application, such as Figure 3 As shown, the processor unit 30 includes an analog-to-digital converter module 32, which is used to convert the voltage signal received at the third terminal of the processor unit 30 into a temperature signal.

[0049] In this embodiment, the analog-to-digital conversion module 32 can be an AD converter, used to convert the voltage signal into a temperature signal. The subsequent processor unit 30 can monitor the temperature of the heating element 50 in real time and generate a suitable PWM signal through the temperature signal, or it can send the temperature signal of the heating element 50 to the display screen of the heater for display, thereby improving the reliability of the heater.

[0050] In some embodiments of this application, when the voltage signal is not greater than the upper voltage limit and the voltage signal is not less than the lower voltage limit, the temperature enable signal is at a high level, and the pulse width modulation controller 31 is also used to output a pulse width modulation signal when the temperature enable signal is at a high level.

[0051] In this embodiment, if the voltage signal is not greater than the upper voltage limit and not less than the lower voltage limit, it indicates that the temperature of the heating element 50 is suitable. Both the first comparator U1 and the second comparator U2 output a high level, thus making the temperature enable signal high. After receiving the high-level temperature enable signal, the pulse width modulation controller 31 can output a pulse width modulation signal to control the power switch normally, ensuring that the temperature of the heating element 50 reaches or remains at the target temperature. This improves the reliability of the heater.

[0052] For example, if the upper limit of the heating element's temperature is +150℃, the corresponding upper limit of the voltage is 4902mV, and the lower limit of the temperature is -20℃, the corresponding lower limit of the voltage is 433mV, then if the voltage signal is between 433mV and 4092mV, the temperature enable signal will be high.

[0053] In some embodiments of this application, the number of temperature detection units 10 and the number of comparison units 20 can both be greater than the number of heating elements, and each temperature detection unit 10 can correspond to one comparison unit 20.

[0054] In this embodiment, since the first comparator U1 and the second comparator U2 adopt open-drain output or open-collector output, the output terminals of multiple sets of comparison units 20 can be connected in parallel. By making the number of temperature detection units 10 and the number of comparison units 20 greater than the number of heating elements, when one of the temperature detection units 10 and the comparison unit 20 malfunctions, the heater protection circuit can still perform the thermal protection function normally, thereby realizing the redundant design of the protection circuit and further improving the reliability of the heater.

[0055] In some embodiments of this application, such as Figure 4 As shown, the temperature detection unit 10 includes a thermocouple TC and an operational amplifier U3. The thermocouple TC is in contact with the heating element 50. The output terminal of the thermocouple TC is connected to the input terminal of the operational amplifier U3. The output terminal of the operational amplifier U3 is the output terminal of the temperature detection unit 10.

[0056] In this embodiment, as an alternative, the temperature detection unit 10 includes a thermocouple TC and an operational amplifier U3. The thermocouple TC can detect the temperature of the heating element 50 and output a thermocouple TC voltage signal. Since the thermocouple TC voltage signal is small, the operational amplifier U3 is used to amplify the thermocouple TC voltage signal and output a voltage signal of appropriate size, thereby improving the flexibility of the heater protection circuit.

[0057] This application also proposes a heater, including a heating element and a heater protection circuit as described in various embodiments of this application.

[0058] For other embodiments of the heater in this application, please refer to the corresponding embodiments of the heater protection circuit in this application.

[0059] Furthermore, although exemplary embodiments have been described herein, their scope includes any and all embodiments based on this disclosure that have equivalent elements, modifications, omissions, combinations (e.g., schemes involving intersections of various embodiments), adaptations, or alterations. Elements in the claims will be interpreted broadly based on the language used in the claims and are not limited to the examples described in this specification or during the implementation of this application, and such examples will be interpreted as non-exclusive. Therefore, this specification and examples are intended to be considered illustrative only, and the true scope and spirit are indicated by the full scope of the following claims and their equivalents.

[0060] The above description is intended to be illustrative and not restrictive. For example, the above examples (or one or more thereof) can be used in combination with each other. Other embodiments may be used by those skilled in the art upon reading the above description. Furthermore, in the above detailed description, various features may be grouped together to simplify the disclosure. This should not be construed as an intention that a feature of the disclosure that is not claimed is necessary for any claim. Rather, the subject matter of this disclosure may be less than all the features of a particular disclosed embodiment. Thus, the following claims are incorporated herein by reference as examples or embodiments, wherein each claim is an independent, separate embodiment, and these embodiments are contemplated to be combined with each other in various combinations or arrangements. The scope of this disclosure should be determined by reference to the appended claims and the full scope of their equivalents.

[0061] The foregoing has provided a detailed description of several embodiments of this disclosure. However, this disclosure is not limited to these specific embodiments. Those skilled in the art can make various variations and modifications based on the concept of this disclosure, and all such variations and modifications should fall within the scope of protection claimed by this disclosure.

Claims

1. A heater protection circuit, characterized in that, include: A temperature detection unit is used to detect the temperature of the heating element in the heater and output a voltage signal corresponding to the temperature. The comparison unit is used to compare the voltage signal with the upper voltage limit and the lower voltage limit respectively, and output a temperature enable signal corresponding to the comparison result. When the voltage signal is greater than the upper voltage limit or the voltage signal is less than the lower voltage limit, the temperature enable signal is low. The processor unit includes a pulse width modulation controller, which is configured to stop outputting a pulse width modulation signal when the temperature enable signal is low, so as to disconnect the power switch of the heating element. The temperature detection unit is in contact with the heating element. The output of the temperature detection unit is connected to the first end of the comparison unit. The second end of the comparison unit is connected to the input of the pulse width modulation controller via the first end of the processor unit. The output of the pulse width modulation controller is connected to the power switch as the second end of the processor unit.

2. The heater protection circuit as described in claim 1, characterized in that, The comparison unit includes a first comparator, a second comparator, and a first resistor. The positive input terminal of the first comparator is connected to the upper voltage limit. The negative input terminal of the first comparator and the positive input terminal of the second comparator are connected to the first terminal of the comparison unit. The negative input terminal of the second comparator is connected to the lower voltage limit. The output terminals of the first comparator, the second comparator, and the first terminal of the first resistor are all connected to the second terminal of the comparison unit. The second terminal of the first resistor is connected to a first power supply. The first comparator and the second comparator adopt open-drain output or open-collector output.

3. The heater protection circuit as described in claim 1, characterized in that, The temperature detection unit includes a second resistor and a third resistor. The second resistor is a negative temperature coefficient thermistor. The second resistor is attached to the surface of the heating element. The first end of the second resistor is connected to a second power supply. The second end of the second resistor and the first end of the third resistor are connected to the output terminal of the temperature detection unit. The second end of the third resistor is grounded.

4. The heater protection circuit as described in claim 3, characterized in that, The temperature detection unit further includes a fourth resistor and a first capacitor. The second end of the second resistor and the first end of the third resistor are connected to the output terminal of the temperature detection unit via the fourth resistor. One end of the first capacitor is connected to the output terminal of the temperature detection unit, and the other end of the first capacitor is grounded.

5. The heater protection circuit as described in claim 1, characterized in that, The output of the temperature detection unit is also connected to the third terminal of the processor unit.

6. The heater protection circuit as described in claim 5, characterized in that, The processor unit includes an analog-to-digital converter module, which is used to convert the voltage signal received at the third terminal of the processor unit into a temperature signal.

7. The heater protection circuit as described in claim 1, characterized in that, When the voltage signal is not greater than the upper voltage limit and not less than the lower voltage limit, the temperature enable signal is at a high level, and the pulse width modulation controller is also used to output a pulse width modulation signal when the temperature enable signal is at a high level.

8. The heater protection circuit as described in claim 2, characterized in that, The number of temperature detection units and the number of comparison units are both greater than the number of heating elements, and each temperature detection unit corresponds to one comparison unit.

9. The heater protection circuit as described in claim 1, characterized in that, The temperature detection unit includes a thermocouple and an operational amplifier. The thermocouple is in contact with the heating element, and the output terminal of the thermocouple is connected to the input terminal of the operational amplifier. The output terminal of the operational amplifier is the output terminal of the temperature detection unit.

10. A heater, characterized in that, It includes a heating element and a heater protection circuit as described in any one of claims 1-9.

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