Over-temperature protection circuit and heating electric appliance

Abstract

The utility model discloses an over-temperature protection circuit and a heating electric appliance, and relates to the technical field of electronic circuits. The over-temperature protection circuit is applied to a thick film heating body integrated with an electronic omnibearing sensing technology. The over-temperature protection circuit comprises an amplification branch circuit, a rectification branch circuit, a square wave generation branch circuit and a control branch circuit. The amplification branch is connected with the thick film heating body and is configured to amplify a temperature detection signal output through the electronic omnibearing sensing technology and output an amplified signal. The rectification branch is configured to rectify the amplified signal and output a DC signal. The square wave generation branch inputs a triangular wave signal and a direct current signal, and is configured to compare the triangular wave signal with the direct current signal, generate a first square wave signal based on a comparison result of the triangular wave signal and the direct current signal, and output the first square wave signal. And the control branch is configured to receive the first square wave signal and perform over-temperature protection on the thick film heating body based on the duty ratio of the first square wave signal. In this way, the stability and reliability of over-temperature protection can be improved.

Description

Technical Field

[0001] The embodiments of the present application relate to the technical field of electronic circuits, and in particular to an over-temperature protection circuit and a heating appliance. Background Art

[0002] In common heating appliances, such as kettles, coffee machines, water heaters, etc., thick film heaters are usually used to achieve the heating function. Thick film heaters have higher power density and lower thermal mass, and can be smaller and faster while more accurately controlling the temperature. However, after a long period of use, the thick film heater may be damaged due to local overheating caused by the accumulation of water scale inside the thick film heater. Therefore, electronic full area sensor technology (E-FAST) is usually integrated into the thick film heater to detect the temperature of the thick film heater, thereby realizing over-temperature protection of the thick film heater.

[0003] At present, the signal output by E-FAST is usually converted into a signal that can be compared with a preset voltage value, and the thick film heater is controlled to stop running when the signal exceeds the preset voltage value to achieve over-temperature protection. However, the stability and reliability of this method are poor. Utility Model Content

[0004] The embodiments of the present application provide an over-temperature protection circuit and a heating appliance, which can improve the stability and reliability of over-temperature protection.

[0005] In a first aspect, an embodiment of the present application provides an over-temperature protection circuit, which is applied to a thick film heater integrated with electronic omnidirectional sensing technology, and the over-temperature protection circuit includes:

[0006] an amplifying branch, connected to the thick film heater, and configured to amplify the temperature detection signal output by the electronic omnidirectional sensing technology and output an amplified signal;

[0007] A rectifying branch, connected to the amplifying branch and configured to rectify the amplified signal and output a DC signal;

[0008] a square wave generating branch, connected to the rectifying branch, inputting a triangular wave signal and the DC signal, and configured to compare the triangular wave signal with the DC signal, and to generate and output a first square wave signal based on the comparison result between the triangular wave signal and the DC signal;

[0009] The control branch is connected to the square wave generating branch and is configured to receive the first square wave signal and determine the temperature of the thick film heater based on the duty cycle of the first square wave signal to protect the thick film heater from over-temperature.

[0010] In one or more embodiments, the over-temperature protection circuit further includes:

[0011] The triangular wave generating branch is respectively connected to the control branch and the square wave generating branch, inputs the second square wave signal output by the control branch, and is configured to convert the second square wave signal into the triangular wave signal.

[0012] In one or more embodiments, the triangular wave generating branch includes a first switch unit and a triangular wave generating unit;

[0013] The first switch unit is connected to the triangular wave generating unit, the control branch, the first power supply and the first ground respectively, and the first switch unit is configured to output a high level to the triangular wave generating unit based on the first power supply when the second square wave signal is at a high level, and to output a low level to the triangular wave generating unit based on the first ground when the second square wave signal is at a low level;

[0014] The triangular wave generating unit is connected to the square wave generating branch and is configured to generate a positive slope portion of the triangular wave signal in response to the low level and to generate a negative slope portion of the triangular wave signal in response to the high level.

[0015] In one or more embodiments, the first switch unit includes a first optical coupler, a first resistor and a second resistor;

[0016] The first resistor is connected between the second power supply and the first end of the light emitter of the first optocoupler, the second end of the light emitter of the first optocoupler is connected to the control branch, the second resistor is connected between the first power supply and the first end of the light receiver of the first optocoupler, the first end of the light receiver of the first optocoupler is also connected to the triangular wave generating unit, and the second end of the light receiver of the first optocoupler is connected to the first ground.

[0017] In one or more embodiments, the triangle wave generating unit includes a first operational amplifier, a third resistor, a fourth resistor, a fifth resistor, a sixth resistor, a first capacitor and a second capacitor;

[0018] The third resistor is connected between the first switch unit and the inverting input terminal of the first operational amplifier, the fourth resistor and the fifth resistor are connected in series between the first power supply and the first ground, the connection point between the fourth resistor and the fifth resistor is connected to the non-inverting input terminal of the first operational amplifier, the sixth resistor is connected between the inverting input terminal and the output terminal of the first operational amplifier, the first capacitor is connected in parallel with the sixth resistor, the second capacitor is connected between the power supply terminal of the first operational amplifier and the first ground, the power supply terminal of the first operational amplifier is also connected to the first power supply, and the ground terminal of the first operational amplifier is connected to the first ground.

[0019] In one or more embodiments, the amplifying branch includes a second operational amplifier, a seventh resistor, an eighth resistor, a ninth resistor, a tenth resistor, an eleventh resistor, a twelfth resistor, a third capacitor, a fourth capacitor, a fifth capacitor, a sixth capacitor and a seventh capacitor;

[0020] The seventh resistor, the fourth capacitor and the ninth resistor are connected in series in sequence between the thick film heater and the inverting input terminal of the second operational amplifier, the eighth resistor is connected between the connection point between the seventh resistor and the fourth capacitor and the first ground, the third capacitor is connected in parallel with the eighth resistor, the tenth resistor and the eleventh resistor are connected in series between the first power supply and the first ground, the connection point between the tenth resistor and the eleventh resistor is connected to the non-inverting input terminal of the second operational amplifier, the sixth capacitor is connected between the power supply terminal of the second operational amplifier and the first ground, the power supply terminal of the second operational amplifier is connected to the first power supply, the ground terminal of the second operational amplifier is connected to the first ground, the twelfth resistor is connected between the inverting input terminal and the output terminal of the second operational amplifier, the fifth capacitor is connected in parallel with the twelfth resistor, and the seventh capacitor is connected between the output terminal of the second operational amplifier and the rectifier branch.

[0021] In one or more embodiments, the rectifying branch includes a first diode and a second diode;

[0022] The anode of the first diode is connected to the cathode of the second diode and the amplifying branch respectively, the cathode of the first diode is connected to the square wave generating branch, and the anode of the second diode is connected to the first ground.

[0023] In one or more embodiments, the square wave generating branch comprises:

[0024] a comparison unit, connected to the rectifying branch, inputting the triangular wave signal and the DC signal, and configured to compare the triangular wave signal with the DC signal and output the comparison result;

[0025] The second switch unit is respectively connected to the comparison unit, the second power supply and the second ground, and is configured to receive the comparison result, and output a low level based on the second ground when the comparison result is a high level, and output a high level based on the second power supply when the comparison result is a low level, so as to output the first square wave signal.

[0026] In one or more embodiments, the comparison unit includes a third operational amplifier, a thirteenth resistor, an eighth capacitor, a ninth capacitor, and a tenth capacitor;

[0027] The thirteenth resistor is connected between the in-phase input terminal of the third operational amplifier and the first ground, the eighth capacitor and the ninth capacitor are both connected in parallel with the thirteenth resistor, the tenth capacitor is connected between the power supply terminal of the third operational amplifier and the first ground, the power supply terminal of the third operational amplifier is also connected to the first power supply, and the ground terminal of the third operational amplifier is connected to the first ground.

[0028] In one or more embodiments, the second switch unit includes a second optical coupler, a fourteenth resistor, a fifteenth resistor, a sixteenth resistor and an eleventh capacitor;

[0029] The fourteenth resistor is connected between the first power supply and the first end of the light emitter of the second optocoupler, the first end of the light emitter of the second optocoupler is also connected to the comparison unit, the second end of the light emitter of the second optocoupler is connected to the first ground, the fifteenth resistor, the sixteenth resistor and the eleventh capacitor are connected in series between the second power supply and the second ground in sequence, the connection point between the fifteenth resistor and the sixteenth resistor is connected to the first end of the light receiver of the second optocoupler, the connection point between the sixteenth resistor and the eleventh capacitor is connected to the control branch, and the second end of the light receiver of the second optocoupler is connected to the second ground.

[0030] In a second aspect, an embodiment of the present application provides a heating appliance, comprising a thick film heater integrating electronic omnidirectional sensing technology and an over-temperature protection circuit as described above, wherein the thick film heater is connected to the over-temperature protection circuit.

[0031] The beneficial effect of the present application is that the over-temperature protection circuit of the embodiment of the present application is applied to a thick film heater integrated with electronic omnidirectional sensing technology. The over-temperature protection circuit includes an amplification branch, a rectification branch, a square wave generation branch and a control branch. Among them, the amplification branch is connected to the thick film heater and is configured to amplify the temperature detection signal output by the electronic omnidirectional sensing technology and output the amplified signal. The rectification branch is connected to the amplification branch and is configured to rectify the amplified signal and output a DC signal. The square wave generation branch is connected to the rectification branch, inputs a triangular wave signal and a DC signal, and is configured to compare the triangular wave signal with the DC signal, and generates and outputs a first square wave signal based on the comparison result of the triangular wave signal and the DC signal. The control branch is connected to the square wave generation branch and is configured to receive the first square wave signal and determine the temperature of the thick film heater based on the duty cycle of the first square wave signal. Subsequently, the control branch can further obtain the change trend of the temperature of the thick film heater, and can realize the over-temperature protection of the thick film heater in combination with the actual temperature of the thick film heater and its change trend. Compared with the solution in the related art that implements over-temperature protection based on a fixed preset voltage value, the present application implements over-temperature protection in combination with the actual temperature of the thick film heater and its changing trend, which can more accurately determine whether the thick film heater is overheated, and thus can implement over-temperature protection more stably and reliably. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] One or more embodiments are exemplarily described by the figures in the corresponding drawings, and these exemplary descriptions are not intended to limit the embodiments. Elements with the same reference numerals in the drawings represent similar elements.

[0033] Figure 1 The structure of the over-temperature protection circuit provided in the embodiment of the present application is shown in FIG. Figure 1 ;

[0034] Figure 2 The structure of the over-temperature protection circuit provided in the embodiment of the present application is shown in FIG. Figure 2 ;

[0035] Figure 3 The structure of the over-temperature protection circuit provided in the embodiment of the present application is shown in FIG. Figure 3 ;

[0036] Figure 4 The structure of the over-temperature protection circuit provided in the embodiment of the present application is shown in FIG. Figure 4 ;

[0037] Figure 5 is with Figure 4 Schematic diagram of circuit structure corresponding to the structure shown. DETAILED DESCRIPTION

[0038] In order to make the purpose, technical scheme and advantages of the embodiments of the present application clearer, the technical scheme in the embodiments of the present application will be described clearly and in detail in combination with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0039] It should be noted that, when an element is described as being “connected to” another element, it may be directly connected to the other element, or one or more intervening elements may exist therebetween.

[0040] In addition, the technical features involved in the various embodiments of the present application described below can be combined with each other as long as there is no structural conflict between them.

[0041] Please refer to Figure 1 , Figure 1 This is a schematic diagram of the structure of the over-temperature protection circuit provided in the embodiment of the present application. Figure 1 As shown, the over-temperature protection circuit 100 is applied to a thick film heater 200 integrated with electronic omnidirectional sensing technology. The thick film heater 200 integrated with electronic omnidirectional sensing technology is a thick film heater with a layer of special material coated on the insulating paint. This material has better electrical conductivity at high temperature and can output a corresponding electrical signal based on the temperature of the thick film heater. The electrical signal is the temperature detection signal in the embodiment of the present application.

[0042] like Figure 1 As shown, the over-temperature protection circuit 100 includes an amplifying branch 10 , a rectifying branch 20 , a square wave generating branch 30 and a controlling branch 40 .

[0043] The amplifying branch 10 is connected to the thick film heater 200 , the rectifying branch 20 is connected to the amplifying branch 10 , the square wave generating branch 30 is connected to the rectifying branch 20 , and the controlling branch 40 is connected to the square wave generating branch 30 .

[0044] Specifically, the amplification branch 10 is configured to amplify the temperature detection signal output by the electronic omnidirectional sensing technology and output the amplified signal. The rectification branch 20 is configured to rectify the amplified signal and output a DC signal. The square wave generation branch 30 inputs the triangular wave signal S1 and the DC signal. The square wave generation branch 30 is configured to compare the triangular wave signal S1 with the DC signal, and generate and output a first square wave signal based on the comparison result between the triangular wave signal S1 and the DC signal. The control branch 40 is configured to receive the first square wave signal and determine the temperature of the thick film heating body 200 based on the duty cycle of the first square wave signal.

[0045] In the related art, the signal output by E-FAST is usually converted into a signal that can be compared with a preset voltage value, and the thick film heater is controlled to stop running when the signal exceeds the preset voltage value to achieve over-temperature protection. That is, over-temperature protection is achieved based on a fixed preset voltage value. However, when this method is applied to different thick film heaters, it is necessary to modify the preset voltage value according to the characteristics of different thick film heaters, and the preset voltage value is usually achieved by a voltage divider resistor. Therefore, when applied to different thick film heaters, it is necessary to select a corresponding voltage divider resistor, and the versatility of the solution is poor. Secondly, since over-temperature protection is only achieved based on a fixed preset voltage value, when the temperature fluctuates within the preset voltage value range, the thick film heater will be constantly switched between running and stopping, and the stability and reliability are poor, which can easily damage the thick film heater, that is, shorten the service life of the thick film heater.

[0046] In the embodiment of the present application, the control branch 40 can determine the temperature of the thick film heater 200 in real time. On the one hand, when applied to different thick film heaters, it is only necessary to adjust the duty cycle of the first square wave signal corresponding to the control branch 40 when implementing over-temperature protection, without changing any electronic devices, and the scheme has strong versatility. On the other hand, the control branch 40 can determine the change trend of the temperature of the thick film heater 200 by determining the temperature of the thick film heater 200 in real time, and realize over-temperature protection in combination with the temperature of the thick film heater 200 and its change trend. Based on this, even if the temperature fluctuates within the preset voltage value range, since the change trend does not meet the over-temperature protection condition, it will not cause the thick film heater to switch between running and stopping, and the stability and reliability are high, which is conducive to extending the service life of the thick film heater. At the same time, combined with whether the change trend of the temperature of the thick film heater 200 is gradually increasing, and whether the temperature of the thick film heater 200 reaches the temperature value of the over-temperature protection, it can accurately determine whether the thick film heater is overheated, and then it can realize over-temperature protection more stably and reliably.

[0047] In one embodiment of the present application, Figure 2 As shown, the over-temperature protection circuit 100 further includes a triangle wave generating branch 50 .

[0048] The triangular wave generating branch 50 is connected to the control branch 40 and the square wave generating branch 30 respectively. The triangular wave generating branch 50 inputs the second square wave signal output by the control branch 40. The triangular wave generating branch 50 is configured to convert the second square wave signal into a triangular wave signal S1. When the period of the second square wave signal remains unchanged, the positive slope and the negative slope of the triangular wave signal S1 are determined by the duty cycle of the second square wave signal. Then, in practical applications, the duty cycle of the second square wave signal can be adjusted to obtain the desired triangular wave signal S1.

[0049] In one embodiment of the present application, Figure 3 As shown, the triangular wave generating branch 50 includes a first switch unit 51 and a triangular wave generating unit 52 .

[0050] The first switch unit 51 is connected to the triangular wave generating unit 52 , the control branch 40 , the first power source V1 and the first ground GND1 , respectively. The triangular wave generating unit 52 is connected to the square wave generating branch 30 .

[0051] Specifically, the first switch unit 51 is configured to output a high level to the triangular wave generating unit 52 based on the first power supply V1 when the second square wave signal is at a high level, and to output a low level to the triangular wave generating unit 52 based on the first ground GND when the second square wave signal is at a low level. The first switch unit 51 can play a role in signal isolation to prevent the signal output by the control branch 40 from interfering with the signal of other branches or units (such as the triangular wave generating unit 52), thereby maintaining the stable operation of the over-temperature protection circuit 100.

[0052] The triangular wave generating unit 52 is configured to generate a positive slope portion of a triangular wave signal in response to a low level, and to generate a negative slope portion of a triangular wave signal in response to a high level. That is, the triangular wave generating unit 52 can output a triangular wave signal based on the high level and the low level output by the first switching unit 51. When the first switching unit 51 outputs a low level, the voltage output by the triangular wave generating unit 52 gradually increases to form a positive slope portion of the triangular wave signal; when the first switching unit 51 outputs a high level, the voltage output by the triangular wave generating unit 52 gradually decreases to form a negative slope portion of the triangular wave signal.

[0053] In one embodiment of the present application, Figure 4 As shown, the square wave generating branch 30 includes a comparing unit 31 and a second switching unit 32 .

[0054] The comparison unit 31 is connected to the rectifier branch 20 and the triangular wave generating unit 52. The comparison unit 31 inputs the triangular wave signal S1 and the DC signal. The comparison unit 31 is configured to compare the triangular wave signal with the DC signal and output a comparison result. In a specific embodiment of the present application, when the voltage of the triangular wave signal is greater than or equal to the voltage of the DC signal, the comparison result output by the comparison unit 31 is a low level; when the voltage of the triangular wave signal is less than the voltage of the DC signal, the comparison result output by the comparison unit 31 is a high level.

[0055] The second switch unit 32 is connected to the comparison unit 31, the second power supply V2 and the second ground GND2 respectively. The second switch unit 32 is configured to receive the comparison result, and output a low level based on the second ground GND2 when the comparison result is a high level, and output a high level based on the second power supply V2 when the comparison result is a low level, so as to output a first square wave signal. The second switch unit 32 can play a role in signal isolation to prevent the signal output by the control branch 40 from interfering with the signal of other branches or units (such as the comparison unit 31), so as to maintain the stable operation of the over-temperature protection circuit 100.

[0056] Please refer to Figure 5 , Figure 5 An example is shown with Figure 4 A circuit corresponding to the structure shown in FIG. Figure 5 As shown, in one embodiment of the present application, the first switch unit 51 includes a first optical coupler U1 , a first resistor R1 , and a second resistor R2 .

[0057] Among them, the first resistor R1 is connected between the second power supply V2 and the first end of the light emitter of the first optocoupler U1, the second end of the light emitter of the first optocoupler U1 is connected to the control branch 40, the second resistor R2 is connected between the first power supply V1 and the first end of the light receiver of the first optocoupler U1, the first end of the light receiver of the first optocoupler U1 is also connected to the triangular wave generating unit 52, and the second end of the light receiver of the first optocoupler U1 is connected to the first ground GND1.

[0058] Specifically, when the second square wave signal output by the control branch 40 is high level, the light emitter of the first optical coupler U1 is turned off, and the light receiver of the first optical coupler U1 is also turned off. The first power source V1 outputs a high level to the triangle wave generating unit 52 at the connection point N1 through the second resistor R2.

[0059] When the second square wave signal output by the control branch 40 is at a low level, the light emitter of the first optical coupler U1 is turned on, and the light receiver of the first optical coupler U1 is also turned on. The connection point N1 between the second resistor R2 and the light receiver of the first optical coupler U1 is connected to the first ground GND1 through the light receiver of the first optical coupler U1, so that a low level is output to the triangle wave generating unit 52 at the connection point N1.

[0060] In an embodiment of the present application, the triangle wave generating unit 52 includes a first operational amplifier UA1 , a third resistor R3 , a fourth resistor R4 , a fifth resistor R5 , a sixth resistor R6 , a first capacitor C1 , and a second capacitor C2 .

[0061] Among them, the third resistor R3 is connected between the first switch unit 51 and the inverting input terminal of the first operational amplifier UA1, the fourth resistor R4 and the fifth resistor R5 are connected in series between the first power supply V1 and the first ground GND1, the connection point between the fourth resistor R4 and the fifth resistor R5 is connected to the non-inverting input terminal of the first operational amplifier UA1, the sixth resistor R6 is connected between the inverting input terminal and the output terminal of the first operational amplifier UA1, the first capacitor C1 and the sixth resistor R6 are connected in parallel, the second capacitor C2 is connected between the power supply terminal of the first operational amplifier UA1 and the first ground GND1, the power supply terminal of the first operational amplifier UA1 is also connected to the first power supply V1, and the ground terminal of the first operational amplifier UA1 is connected to the first ground GND1.

[0062] Specifically, the third resistor R3 is a current limiting resistor. The fourth resistor R4 and the fifth resistor R5 are voltage dividing resistors. The second capacitor C2 is a filter capacitor. The first capacitor C1, the sixth resistor R6 and the first operational amplifier UA1 form an inverse integrator to achieve that when the connection point N1 is at a low level, the voltage output by the first operational amplifier UA1 gradually increases to form a positive slope portion of the triangular wave signal; and when the connection point N1 is at a high level, the voltage output by the first operational amplifier UA1 gradually decreases to form a negative slope portion of the triangular wave signal. Thus, a triangular wave signal is output at the output end of the first operational amplifier UA1.

[0063] In one embodiment of the present application, the amplifying branch 10 includes a second operational amplifier UA2, a seventh resistor R7, an eighth resistor R8, a ninth resistor R9, a tenth resistor R10, an eleventh resistor R11, a twelfth resistor R12, a third capacitor C3, a fourth capacitor C4, a fifth capacitor C5, a sixth capacitor C6 and a seventh capacitor C7.

[0064] Among them, the seventh resistor R7, the fourth capacitor C4 and the ninth resistor R9 are connected in series between the thick film heater 200 and the inverting input terminal of the second operational amplifier UA2 in sequence, the eighth resistor R8 is connected between the connection point between the seventh resistor R7 and the fourth capacitor C4 and the first ground GND1, the third capacitor C3 is connected in parallel with the eighth resistor R8, the tenth resistor R10 and the eleventh resistor R11 are connected in series between the first power supply V1 and the first ground GND1, the connection point between the tenth resistor R10 and the eleventh resistor R11 is connected to the non-inverting input terminal of the second operational amplifier UA2, the sixth capacitor C6 is connected between the power supply terminal of the second operational amplifier UA2 and the first ground GND1, the power supply terminal of the second operational amplifier UA2 is connected to the first power supply V1, the ground terminal of the second operational amplifier UA2 is connected to the first ground GND1, the twelfth resistor R12 is connected between the inverting input terminal and the output terminal of the second operational amplifier UA2, the fifth capacitor C5 is connected in parallel with the twelfth resistor R12, and the seventh capacitor C7 is connected between the output terminal of the second operational amplifier UA2 and the rectifier branch 20.

[0065] Specifically, the seventh resistor R7, the eighth resistor R8, the ninth resistor R9, the third capacitor C3 and the fourth capacitor C4 are used for current limiting and filtering. The tenth resistor R10 and the eleventh resistor R11 are voltage-dividing resistors. The sixth capacitor C6 and the seventh capacitor C7 are filter capacitors. The fifth capacitor C5, the eleventh resistor R12 and the second operational amplifier UA2 form a reverse differential amplifier circuit to increase the temperature detection signal output by the electronic omnidirectional sensing technology by a preset voltage value to form an amplified signal.

[0066] In one embodiment of the present application, the rectifying branch 20 includes a first diode D1 and a second diode D2 .

[0067] The anode of the first diode D1 is connected to the cathode of the second diode D2 and the amplifying branch 10 respectively, the cathode of the first diode D1 is connected to the square wave generating branch 30, and the anode of the second diode D2 is connected to the first ground GND1.

[0068] Specifically, the temperature detection signal is usually a sinusoidal signal, with a positive part and a negative part. Although amplified by the amplification branch 10, there may still be a negative part. Based on this, the positive part of the temperature detection signal is rectified by the first diode D1, and the negative part of the temperature detection signal is rectified by the second diode D2 to output a complete signal.

[0069] In an embodiment of the present application, the comparison unit 31 includes a third operational amplifier UA3, a thirteenth resistor R13, an eighth capacitor C8, a ninth capacitor C9 and a tenth capacitor C10.

[0070] Among them, the thirteenth resistor R13 is connected between the non-inverting input terminal of the third operational amplifier UA3 and the first ground GND1, the eighth capacitor C8 and the ninth capacitor C9 are both connected in parallel with the thirteenth resistor R13, the tenth capacitor C10 is connected between the power supply terminal of the third operational amplifier UA3 and the first ground GND1, the power supply terminal of the third operational amplifier UA3 is also connected to the first power supply V1, and the ground terminal of the third operational amplifier UA3 is connected to the first ground GND1.

[0071] Specifically, the thirteenth resistor R13, the eighth capacitor C8, the ninth capacitor C9 and the tenth capacitor C10 are all used for filtering.

[0072] When the voltage of the DC signal is greater than the voltage of the triangular wave signal, the third operational amplifier UA3 outputs a high level; when the voltage of the DC signal is less than or equal to the voltage of the triangular wave signal, the third operational amplifier UA3 outputs a low level. Then, within a period of the triangular wave signal, according to the duty cycle of the signal output by the third operational amplifier UA3, the voltage of the DC signal can be determined, and then the temperature detection signal can be determined, and finally the temperature of the thick film heater 200 can be determined.

[0073] Secondly, within a period of a triangular wave signal, the duration of the third operational amplifier UA3 outputting a high level gradually increases (correspondingly, the duration of the low level gradually decreases), and the duration of the voltage of the DC signal being greater than the voltage of the triangular wave signal gradually increases, and it can be determined that the temperature of the thick-film heating body 200 corresponding to the temperature detection signal at this time gradually increases; on the contrary, the duration of the third operational amplifier UA3 outputting a high level gradually decreases (correspondingly, the duration of the low level gradually increases), and the duration of the voltage of the DC signal being greater than the voltage of the triangular wave signal gradually decreases, that is, the duration of the voltage of the DC signal being less than or equal to the voltage of the triangular wave signal gradually increases, and it can be determined that the temperature of the thick-film heating body 200 corresponding to the temperature detection signal at this time gradually decreases. In summary, the change trend of the temperature of the thick-film heating body 200 can be determined.

[0074] In an embodiment of the present application, the second switch unit 32 includes a second optical coupler U2 , a fourteenth resistor R14 , a fifteenth resistor R15 , a sixteenth resistor R16 and an eleventh capacitor C11 .

[0075] Among them, the fourteenth resistor R14 is connected between the first power supply V1 and the first end of the light emitter of the second optocoupler U2, the first end of the light emitter of the second optocoupler U2 is also connected to the comparison unit 31, the second end of the light emitter of the second optocoupler U2 is connected to the first ground GND1, the fifteenth resistor R15, the sixteenth resistor R16 and the eleventh capacitor C11 are connected in series between the second power supply V2 and the second ground GND2 in sequence, the connection point between the fifteenth resistor R15 and the sixteenth resistor R16 is connected to the first end of the light receiver of the second optocoupler U2, the connection point between the sixteenth resistor R16 and the eleventh capacitor C11 is connected to the control branch 40, and the second end of the light receiver of the second optocoupler U2 is connected to the second ground GND2.

[0076] Specifically, when the third operational amplifier UA3 outputs a high level, the light emitter of the second optical coupler U2 is turned on, and the light receiver of the second optical coupler U2 is also turned on. The connection point N2 between the fifteenth resistor R15 and the light receiver of the second optical coupler U2 is connected to the second ground GND2 through the light receiver of the second optical coupler U2, so that a low level (the low level is the low level in the first square wave signal) is output at the connection point N2 to the control branch 40.

[0077] When the third operational amplifier UA3 outputs a low level, the light-emitting device of the first optical coupler U1 is turned on, and the light receiver of the first optical coupler U1 is also turned off. The second power supply V2 sequentially outputs a high level (the high level is the high level in the first square wave signal) to the control branch 40 through the fifteenth resistor R15 and the sixteenth resistor R16.

[0078] Then, based on the duty cycle of the first square wave signal, the control branch 40 can determine the voltage of the DC signal, and then determine the temperature detection signal, and finally determine the temperature of the thick film heater 200. Moreover, if the duty cycle of the first square wave signal gradually decreases, it can be determined that the temperature of the thick film heater 200 corresponding to the temperature detection signal at this time gradually increases; conversely, if the duty cycle of the first square wave signal gradually increases, it can be determined that the temperature of the thick film heater 200 corresponding to the temperature detection signal at this time gradually decreases. In summary, the control branch 40 can determine the changing trend of the temperature of the thick film heater 200. Therefore, when applied to different thick film heaters, it is only necessary to adjust the duty cycle of the first square wave signal corresponding to the control branch 40 when realizing over-temperature protection without changing any electronic components, and the solution has strong versatility. Furthermore, by combining the temperature of the thick film heater 200 and its changing trend to achieve over-temperature protection, even if the temperature fluctuates within the preset voltage value range, since the changing trend does not meet the over-temperature protection condition, the thick film heater will not be constantly switched between operation and shutdown, and the stability and reliability are high, which is conducive to extending the service life of the thick film heater. At the same time, by combining whether the changing trend of the temperature of the thick film heater 200 is gradually increasing, and whether the temperature of the thick film heater 200 has reached the temperature value of the over-temperature protection, it is possible to accurately determine whether the thick film heater is over-heated, and thus achieve over-temperature protection more stably and reliably.

[0079] The embodiment of the present application also provides a heating appliance. The heater includes a thick film heater integrated with electronic omnidirectional sensing technology and an over-temperature protection circuit 100 in any embodiment of the present application. The thick film heater is connected to the over-temperature protection circuit 100.

[0080] The above descriptions are merely embodiments of the present application and are not intended to limit the patent scope of the present application. Any equivalent structure or equivalent process transformation made using the contents of the present application specification and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present application.

[0081] The above embodiments are only used to illustrate the technical solutions of the present application, but not to limit them. Under the idea of ​​the present application, the technical features in the above embodiments or different embodiments can also be combined, and the steps can be implemented in any order. It should be understood by ordinary technicians in this field that they can still modify the technical solutions recorded in the above embodiments, or replace some of the technical features by equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. An over-temperature protection circuit, characterized in that: Applied to a thick film heater integrated with electronic omnidirectional sensing technology, the over-temperature protection circuit comprises: an amplifying branch, connected to the thick film heater, and configured to amplify the temperature detection signal output by the electronic omnidirectional sensing technology and output an amplified signal; A rectifying branch, connected to the amplifying branch and configured to rectify the amplified signal and output a DC signal; a square wave generating branch, connected to the rectifying branch, inputting a triangular wave signal and the DC signal, and configured to compare the triangular wave signal with the DC signal, and to generate and output a first square wave signal based on the comparison result between the triangular wave signal and the DC signal; The control branch is connected to the square wave generating branch and is configured to receive the first square wave signal and determine the temperature of the thick film heater based on the duty cycle of the first square wave signal to protect the thick film heater from over-temperature.

2. The over-temperature protection circuit according to claim 1, characterized in that: Also includes: The triangular wave generating branch is respectively connected to the control branch and the square wave generating branch, inputs the second square wave signal output by the control branch, and is configured to convert the second square wave signal into the triangular wave signal.

3. The over-temperature protection circuit according to claim 2, characterized in that: The triangular wave generating branch comprises a first switch unit and a triangular wave generating unit; The first switch unit is connected to the triangular wave generating unit, the control branch, the first power supply and the first ground respectively, and the first switch unit is configured to output a high level to the triangular wave generating unit based on the first power supply when the second square wave signal is at a high level, and to output a low level to the triangular wave generating unit based on the first ground when the second square wave signal is at a low level; The triangular wave generating unit is connected to the square wave generating branch and is configured to generate a positive slope portion of the triangular wave signal in response to the low level and to generate a negative slope portion of the triangular wave signal in response to the high level.

4. The over-temperature protection circuit according to claim 3, characterized in that: The first switch unit includes a first optical coupler, a first resistor and a second resistor; The first resistor is connected between the second power supply and the first end of the light emitter of the first optocoupler, the second end of the light emitter of the first optocoupler is connected to the control branch, the second resistor is connected between the first power supply and the first end of the light receiver of the first optocoupler, the first end of the light receiver of the first optocoupler is also connected to the triangular wave generating unit, and the second end of the light receiver of the first optocoupler is connected to the first ground.

5. The over-temperature protection circuit according to claim 3, characterized in that: The triangle wave generating unit comprises a first operational amplifier, a third resistor, a fourth resistor, a fifth resistor, a sixth resistor, a first capacitor and a second capacitor; The third resistor is connected between the first switch unit and the inverting input terminal of the first operational amplifier, the fourth resistor and the fifth resistor are connected in series between the first power supply and the first ground, the connection point between the fourth resistor and the fifth resistor is connected to the non-inverting input terminal of the first operational amplifier, the sixth resistor is connected between the inverting input terminal and the output terminal of the first operational amplifier, the first capacitor is connected in parallel with the sixth resistor, the second capacitor is connected between the power supply terminal of the first operational amplifier and the first ground, the power supply terminal of the first operational amplifier is also connected to the first power supply, and the ground terminal of the first operational amplifier is connected to the first ground.

6. The over-temperature protection circuit according to claim 1, characterized in that: The amplifying branch includes a second operational amplifier, a seventh resistor, an eighth resistor, a ninth resistor, a tenth resistor, an eleventh resistor, a twelfth resistor, a third capacitor, a fourth capacitor, a fifth capacitor, a sixth capacitor and a seventh capacitor; The seventh resistor, the fourth capacitor and the ninth resistor are connected in series in sequence between the thick film heater and the inverting input terminal of the second operational amplifier, the eighth resistor is connected between the connection point between the seventh resistor and the fourth capacitor and the first ground, the third capacitor is connected in parallel with the eighth resistor, the tenth resistor and the eleventh resistor are connected in series between the first power supply and the first ground, the connection point between the tenth resistor and the eleventh resistor is connected to the non-inverting input terminal of the second operational amplifier, the sixth capacitor is connected between the power supply terminal of the second operational amplifier and the first ground, the power supply terminal of the second operational amplifier is connected to the first power supply, the ground terminal of the second operational amplifier is connected to the first ground, the twelfth resistor is connected between the inverting input terminal and the output terminal of the second operational amplifier, the fifth capacitor is connected in parallel with the twelfth resistor, and the seventh capacitor is connected between the output terminal of the second operational amplifier and the rectifier branch.

7. The over-temperature protection circuit according to claim 1, characterized in that: The rectifying branch comprises a first diode and a second diode; The anode of the first diode is connected to the cathode of the second diode and the amplifying branch respectively, the cathode of the first diode is connected to the square wave generating branch, and the anode of the second diode is connected to the first ground.

8. The over-temperature protection circuit according to claim 1, characterized in that: The square wave generating branch comprises: a comparison unit, connected to the rectifying branch, inputting the triangular wave signal and the DC signal, and configured to compare the triangular wave signal with the DC signal and output the comparison result; The second switch unit is respectively connected to the comparison unit, the second power supply and the second ground, and is configured to receive the comparison result, and output a low level based on the second ground when the comparison result is a high level, and output a high level based on the second power supply when the comparison result is a low level, so as to output the first square wave signal.

9. The over-temperature protection circuit according to claim 8, characterized in that: The comparison unit includes a third operational amplifier, a thirteenth resistor, an eighth capacitor, a ninth capacitor and a tenth capacitor; The thirteenth resistor is connected between the in-phase input terminal of the third operational amplifier and the first ground, the eighth capacitor and the ninth capacitor are both connected in parallel with the thirteenth resistor, the tenth capacitor is connected between the power supply terminal of the third operational amplifier and the first ground, the power supply terminal of the third operational amplifier is also connected to the first power supply, and the ground terminal of the third operational amplifier is connected to the first ground.

10. The over-temperature protection circuit according to claim 8, characterized in that: The second switch unit includes a second optical coupler, a fourteenth resistor, a fifteenth resistor, a sixteenth resistor and an eleventh capacitor; The fourteenth resistor is connected between the first power supply and the first end of the light emitter of the second optocoupler, the first end of the light emitter of the second optocoupler is also connected to the comparison unit, the second end of the light emitter of the second optocoupler is connected to the first ground, the fifteenth resistor, the sixteenth resistor and the eleventh capacitor are connected in series between the second power supply and the second ground in sequence, the connection point between the fifteenth resistor and the sixteenth resistor is connected to the first end of the light receiver of the second optocoupler, the connection point between the sixteenth resistor and the eleventh capacitor is connected to the control branch, and the second end of the light receiver of the second optocoupler is connected to the second ground.

11. A heating appliance, characterized in that: It comprises a thick film heater integrated with electronic omnidirectional sensing technology and an over-temperature protection circuit as described in any one of claims 1 to 10, wherein the thick film heater is connected to the over-temperature protection circuit.

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