CN108306258B - Over-temperature detection circuit and over-temperature protection circuit for heater - Google Patents
Over-temperature detection circuit and over-temperature protection circuit for heater Download PDFInfo
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- CN108306258B CN108306258B CN201810298704.XA CN201810298704A CN108306258B CN 108306258 B CN108306258 B CN 108306258B CN 201810298704 A CN201810298704 A CN 201810298704A CN 108306258 B CN108306258 B CN 108306258B
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H5/00—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal non-electric working conditions with or without subsequent reconnection
- H02H5/04—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal non-electric working conditions with or without subsequent reconnection responsive to abnormal temperature
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Abstract
The present application relates to an overheat detection circuit and an overheat protection circuit for a heater. The over-temperature detection circuit and the over-temperature protection circuit have the beneficial effects that the over-temperature detection circuit and the over-temperature protection circuit do not need to use a temperature sensor, and whether the heater has an over-temperature condition can be judged only by detecting the difference between the power supply voltage and the voltage at two ends of the heater. In addition, the over-temperature protection for the heater can be realized with the addition of only an external circuit and a protection switch. This can significantly reduce heater volume without losing a single failsafe function. Provides a novel idea in the aspect of miniaturized heater, and has high practical value and economic value.
Description
Technical Field
The present application relates to the technical field of electrical engineering, and in particular, to an over-temperature detection circuit and an over-temperature protection circuit for a heater.
Background
Heater temperature control is widely used in various industries. But safety issues with heaters are also of concern.
According to the traditional safety requirements, the heater should not have the phenomena of uncontrolled temperature and rise or even fire under the single failure of any device.
The traditional solution is mainly to connect a temperature switch in the power supply loop of the heater in series for detecting the temperature of the heater, and when the temperature of the heater reaches a certain limit value, the power supply of the heater is disconnected. The temperature switch has two forms, one is self-recovering and one is non-self-recovering. In either way, there are a number of drawbacks, such as the thermal protection point depends on the nature of the temperature switch itself, which cannot be readjusted externally; the self-recovery type heater can work near the critical point of the over-temperature protection temperature and still deviate from the normal higher-level operation, hidden danger can still be brought for a long time, or higher requirements are put on the temperature resistance of surrounding electronic equipment; the non-self-recovery type self-fusing protection device is automatically fused once protected, the protection device must be replaced after maintenance, the temperature switch is large in general size and difficult to apply in some micro heaters, and the temperature switch is expensive and has adverse effects on the control of the heater cost.
Also, the conventional method relies on a temperature sensor for temperature control, which must be added to the heater, further increasing the heater volume and the cost of the heating circuit.
For this reason, there is an urgent need in the art to develop a temperature sensor-free overheat detection circuit and an overheat protection circuit for a heater.
Disclosure of Invention
An object of the present invention is to provide an overheat detection circuit for a heater without using a temperature sensor, thereby solving the technical problems in the prior art. Specifically, the circuit of the application judges whether the heater is over-temperature or not by adding a voltage detection comparison circuit. The heater is typically a positive temperature coefficient heater, i.e., as the temperature increases, the resistance increases. The over-temperature detection circuit supplies power to the heater through the constant current circuit, then the voltage comparator compares the difference between the power supply voltage and the voltages at two ends of the heater with the set temperature protection point voltage, and if the difference between the power supply voltage and the voltages at two ends of the heater is lower than the temperature protection point voltage, the over-temperature condition of the heater is indicated.
The invention also aims to provide an over-temperature protection circuit for the heater, which uses the over-temperature detection circuit.
In order to achieve the above object, the present application provides the following technical solutions.
In a first aspect, the present application provides an over-temperature protection circuit for a heater, the over-temperature protection circuit for a heater including a heater, a constant current circuit for supplying power to the heater, a voltage comparator, a protection switch, and a first resistor, the voltage comparator including a "+" terminal input, a "-" terminal input, and an output, the output of the voltage comparator outputting an over-temperature signal when an over-temperature condition occurs to the heater;
wherein the protection switch is connected in series with the heater;
wherein the first resistor is configured in parallel with the heater;
the "+" end input end of the voltage comparator is used for inputting the difference between the power supply voltage and the voltages at the two ends of the heater, and the "-" end input end of the voltage comparator is used for inputting the temperature protection point voltage; and
the output end of the voltage comparator is electrically communicated with the protection switch and is configured to turn off the protection switch when the output end of the voltage comparator outputs an over-temperature signal.
In one embodiment of the first aspect, the heater is a positive temperature coefficient heater.
In another implementation of the first aspect, the protection switch is a CMOS device and/or a solid state relay.
In another embodiment of the first aspect, the protection switch is a CMOS device, the gate of the CMOS device and the output of the voltage comparator are in electrical communication, and the over-temperature protection circuit for the heater further comprises a second resistor having one end in electrical communication with the gate of the CMOS device and the other end in electrical communication with the output of the voltage comparator.
In another embodiment of the first aspect, the over-temperature protection circuit for a heater further includes a digital-to-analog converter, an external temperature control circuit, and a micro control unit;
the digital-analog converter is used for outputting temperature protection point voltage;
wherein the micro-control unit is configured to receive an over-temperature signal at the output of the voltage comparator and to provide an external temperature control input signal; and
wherein the external temperature control circuit is configured to reset the protection switch.
In another implementation manner of the first aspect, the over-temperature protection circuit for a heater further includes a digital-to-analog converter, an external start-stop circuit, and a control logic circuit;
the digital-analog converter is used for outputting temperature protection point voltage;
the external start-stop circuit is used for providing a fixed pulse width input signal, and the fixed pulse width input signal is used for controlling the on-off of the constant current circuit;
wherein the control logic circuit comprises a CMOS and gate device and at least one schmidt gate device in series, one end of the at least one schmidt gate device being in electrical communication with the output of the voltage comparator and the other end being in electrical communication with the input of the CMOS and gate device; and
wherein the fixed pulse width input signal is in electrical communication with an input of the CMOS and gate device and an output of the CMOS and gate device is in electrical communication with the constant current circuit.
In another implementation manner of the first aspect, when an over-temperature condition occurs in the heater, the output end of the voltage comparator outputs a low level as an over-temperature signal, and the protection switch is turned off.
In another implementation manner of the first aspect, when the heater generates an over-temperature condition, the output end of the voltage comparator outputs a low level serving as an over-temperature signal, the protection switch is opened, and the micro control unit re-closes the protection switch through the external temperature control circuit after receiving the over-temperature signal.
In another implementation manner of the first aspect, when the heater generates an over-temperature condition, the output end of the voltage comparator outputs a low level as an over-temperature signal, the protection switch is opened, and the external temperature control circuit re-closes the protection switch when detecting that the temperature of the heater falls below an acceptable maximum temperature.
In another implementation manner of the first aspect, when the heater has an over-temperature condition, the output end of the voltage comparator outputs a low level serving as an over-temperature signal, the protection switch is opened, the next fixed pulse width input signal provided by the external power-on circuit enables the constant current circuit to be electrically connected again, the protection switch is closed again, and the heater is started again.
In a second aspect, the present application provides an over-temperature detection circuit for a heater, the over-temperature detection circuit comprising a heater, a constant current circuit to power the heater, and a voltage comparator comprising a "+" terminal input, a "-" terminal input, and an output,
the "+" end input end of the voltage comparator is used for inputting the difference between the power supply voltage and the voltage at two ends of the heater, and the "-" end input end of the voltage comparator is used for inputting the temperature protection point voltage.
In one embodiment of the second aspect, the voltage comparator output outputs a low level when an over-temperature condition occurs in the heater.
Compared with the prior art, the over-temperature detection circuit and the over-temperature protection circuit have the beneficial effects that the over-temperature detection circuit and the over-temperature protection circuit do not need to use a temperature sensor, whether the heater has an over-temperature condition can be judged only by detecting the difference between the power supply voltage and the voltages at two ends of the heater, and under the condition that an external circuit and a protection switch are only needed to be added, the over-temperature protection for the heater in a self-recovery or non-self-recovery mode can be realized, so that the volume of the heater can be obviously reduced, and meanwhile, the single fault protection function is not lost. Provides a novel idea in the aspect of miniaturized heater, and has high practical value and economic value.
Drawings
Fig. 1 schematically shows a constant current circuit according to one embodiment of the present application.
Fig. 2 schematically shows an over-temperature detection circuit according to an embodiment of the present application.
Fig. 3 schematically shows an over-temperature protection circuit according to one embodiment of the present application.
Fig. 4 schematically shows a schematic diagram of a non-self-healing over-temperature protection circuit according to one embodiment of the present application.
Fig. 5 schematically illustrates a non-self-healing over-temperature protection circuit according to another embodiment of the present application.
Fig. 6 schematically shows a schematic diagram of a temperature control circuit according to an embodiment of the present application.
Fig. 7 schematically illustrates a temperature control circuit according to another embodiment of the present application.
Detailed Description
The technical solutions of the present application will be clearly and completely described below with reference to the accompanying drawings and examples of the present application.
Definition of terms
As used herein, the term "temperature guard point voltage" refers to the difference between the supply voltage and the voltage across the heater when the heater is at an acceptable maximum temperature in the case of heating the heater with a constant current circuit. The temperature protection point voltage may be greater than zero and less than the supply voltage of the constant current circuit.
As used herein, the term "over temperature signal" refers to a signal output by the output of a voltage comparator when an over temperature condition occurs in the heater. In general, the over-temperature signal refers to a low level output from the output terminal of the voltage comparator.
In a first aspect, the present application provides an over-temperature protection circuit for a heater, the over-temperature protection circuit for a heater including a heater, a constant current circuit for supplying power to the heater, a voltage comparator, a protection switch, and a first resistor, the voltage comparator including a "+" terminal input, a "-" terminal input, and an output, the output of the voltage comparator outputting an over-temperature signal when an over-temperature condition occurs to the heater;
wherein the protection switch is connected in series with the heater;
wherein the first resistor is configured in parallel with the heater;
the "+" end input end of the voltage comparator is used for inputting the difference between the power supply voltage and the voltages at the two ends of the heater, and the "-" end input end of the voltage comparator is used for inputting the temperature protection point voltage; and
the output end of the voltage comparator is electrically communicated with the protection switch and is configured to turn off the protection switch when the output end of the voltage comparator outputs an over-temperature signal.
In another embodiment of the first aspect, the over-temperature protection circuit for a heater further includes a digital-to-analog converter, an external temperature control circuit, and a micro control unit;
the digital-analog converter is used for outputting temperature protection point voltage;
wherein the micro control unit is configured to receive an over-temperature signal at the output of the voltage comparator; and
wherein the external temperature control circuit is configured to reset the protection switch.
In another implementation manner of the first aspect, the over-temperature protection circuit for a heater further includes a digital-to-analog converter, an external start-stop circuit, and a control logic circuit;
the digital-analog converter is used for outputting temperature protection point voltage;
the external start-stop circuit is used for providing a fixed pulse width input signal, and the fixed pulse width input signal is used for controlling the on-off of the constant current circuit;
wherein the control logic circuit comprises a CMOS and gate device and at least one schmidt gate device in series, one end of the at least one schmidt gate device being in electrical communication with the output of the voltage comparator and the other end being in electrical communication with the input of the CMOS and gate device; and
wherein the fixed pulse width input signal is in electrical communication with an input of the CMOS and gate device and an output of the CMOS and gate device is in electrical communication with the constant current circuit.
In a second aspect, the present application provides an over-temperature detection circuit for a heater, the over-temperature detection circuit comprising a heater, a constant current circuit to power the heater, and a voltage comparator comprising a "+" terminal input, a "-" terminal input, and an output,
the "+" end input end of the voltage comparator is used for inputting the difference between the power supply voltage and the voltage at two ends of the heater, and the "-" end input end of the voltage comparator is used for inputting the temperature protection point voltage.
In one embodiment, the present application provides a heater overtemperature protection circuit, which is characterized by comprising:
the temperature sensor or the temperature switch is not required to be added;
a heater adapted to a positive temperature coefficient of resistance;
the constant current mode is used for supplying power to the heater, and meanwhile, the constant current source can control the switch by an external signal;
detecting voltage change of a voltage detection point caused by resistance change of the heater by a voltage detection comparison circuit, and outputting a control signal to the protection switch by a set over-temperature voltage;
the protection switch turns off the heater current to realize over-temperature protection;
once the circuit detects the over-temperature, unless reset, the power supply of the heater is always disconnected, repeated on-off is avoided, and the problem that temperature protection only repeatedly rises and falls at the over-temperature boundary is caused;
the circuit can realize on-line protection reset, namely, under the condition of not performing any power-off operation, the protection circuit is reset through an external reset signal, so that the heater can work normally;
the protection circuit does not change an external control circuit, does not influence the original external temperature closed-loop control circuit and control mode method or program of the temperature control system, and can be realized only by improving a power supply circuit of the heater;
in one embodiment, the heater should be one whose internal resistance increases with increasing temperature, i.e., a positive temperature coefficient heater. The heaters should all be positive temperature coefficients, depending on the heater material characteristics. As more and more electrons participate in thermal disorder movement with temperature rise at the atomic level, fewer electrons are presented to move in one direction under voltage control, and the effect is that the current is reduced, i.e. the resistance is increased. The present patent should be adapted to virtually all heaters.
In a specific embodiment, the constant current circuit can perform start-stop control through an external control signal, constant current control is performed during start, and the constant current circuit does not output during stop. This is used to provide an external control circuit with a means of temperature closed loop control.
In one embodiment, the constant current should be less than the minimum current in the operating region of the heater, i.e., the current should be constant and unchanged by the resistance change of the heater when the heater is operating normally;
in one embodiment, the over-temperature voltage can be reset, and even on-line reset is performed through the controller and the digital-to-analog conversion device, so that the purpose of setting different protection temperatures is achieved.
In one embodiment, after the over-temperature protection circuit described herein enters a protection state, the start-stop signal is turned off again, and then turned on again, so that the protection switch can be reset. In this embodiment, the resetting does not need to change any original software and hardware, and only needs to add a protection circuit and a protection switch.
In a specific embodiment, by improving the over-temperature detection circuit according to the first aspect, a temperature control circuit of a non-self-recovery type temperature-less sensor is realized, which is characterized in that,
no temperature sensor;
the temperature is automatically disconnected after being increased to a certain set point and cannot be recovered, and an external circuit can detect the disconnection state and judge whether continuous control of the temperature is needed or not;
the voltage of the temperature protection point in the voltage detection comparison circuit is set on line by an external digital-analog circuit, so that any temperature control of the circuit can be realized;
in a specific embodiment, by improving the over-temperature detection circuit according to the first aspect, a temperature control circuit of a self-recovery type temperature-less sensor is realized, which is characterized in that,
adding logic judgment, adding a fixed pulse width input signal and enabling an over-temperature signal output by the voltage detection comparison circuit to participate in control at the control front section of the constant current circuit;
when the over-temperature signal arrives, the external start-stop signal is in any state, the constant current circuit stops working, the next pulse width signal resets the circuit, the heater is started again, and protection is enabled immediately after the over-temperature signal arrives, so that the pulse width of the phase-change pulse width control reaches the aim of temperature control.
The over-temperature protection circuit described herein first requires a controlled constant current circuit to supply power. While this circuit needs to be controlled, which can be turned on and off from the outside. Referring to fig. 1, fig. 1 schematically shows a constant current circuit according to one embodiment of the present application. As shown in the figure, the function of current switching control is realized by Q2. When the control input is at a high level, the voltage of the Q1 is the output voltage of the U1, and the output of the U1 is the current control signal of the Q1. The constant current function is realized through R1, Q1, U1 and V1. R1 is a current sampling resistor, and V1 is a control voltage. When the output current is smaller, the "-" terminal voltage of the U1 is smaller than V1, the output voltage of the U1 amplifier is increased, when the current becomes larger, the-terminal voltage of the U1 becomes larger, the state equal to V1 is gradually reached, and the output of the U1 is gradually reduced until a stable state is entered. R2 is an isolation resistor to achieve that the gate voltage of Q1 can be pulled down by Q2.
The constant current circuit has the following characteristics: 1) The controlled end of the circuit can input PWM control signals without changing any original control circuit and software program. 2) V1 may be modified to be output by the DAC and the current output may be adjustable.
For ease of control, the constant current source should be designed at the negative supply terminal, i.e. the ground. In another case, when the impedance of the public ground needs to be reduced, the constant current source designed at the positive end can be used in the method disclosed by the patent, and only the control logic needs to be slightly modified and a bootstrap circuit at the control end is added.
The heater is not strictly limited in this application, but only the positive temperature coefficient of resistance is required. The circuit that this patent was published can realize no temperature sensor or temperature switch just can realize temperature protection's principle, realizes promptly that the resistance to heater itself carries out on-line monitoring, when the resistance is greater than a definite value, just cuts off this heater power supply to reach the purpose of protection.
Next, an over-temperature detection circuit and an over-temperature detection method for a heater according to the present application will be discussed in detail with reference to fig. 2. Fig. 2 schematically shows an over-temperature detection circuit according to an embodiment of the present application. As shown in fig. 2, the over-temperature detection circuit includes a heater, a constant current circuit that supplies power to the heater, and a voltage comparator U2. The "+" end of U2 is used for inputting the difference Vp between the power supply voltage and the voltage at the two ends of the heater, and the "-" end is used for inputting the temperature protection point voltage V2.
Whether the heater has an over-temperature condition can be judged by detecting the voltage V0 at the output end of the voltage comparator. The circuit will be subjected to transient analysis. When the heater is just started, the resistance is smaller, so that the voltage at two ends of the heater is smaller, the difference Vp between the power supply voltage and the voltage at two ends of the heater is larger than the temperature protection point voltage V2, and the output end of the voltage comparator U2 outputs a high level, namely the position V0 is a high level. As the heater temperature increases, vp gradually decreases until it is less than V2, at which time the output of the voltage comparator U2 outputs a low level, i.e., V0 is low. Therefore, it is possible to determine whether the heater has an over-temperature condition by detecting the voltage V0 at the output terminal of the voltage comparator U2 without using a temperature sensor.
An over-temperature protection circuit for a heater and an over-temperature protection method for a heater according to the present application will be described in detail below with reference to fig. 3 to 7.
Fig. 3 schematically shows an over-temperature protection circuit according to one embodiment of the present application. As shown in fig. 3, Q3 is a protection switch, which may be replaced with other devices such as solid state relays, contact relays, and the like. U2 is a voltage comparator, and U2 and V2 form a voltage monitoring circuit.
The over-temperature protection circuit shown in fig. 3 has a steady state, which is the key to whether the circuit can be reset. The circuit will be subjected to transient analysis. In the case where the constant current circuit is off, if Q3 is on, Q3 and the heater make Vp directly equal to the supply voltage (high level). If Q3 is off, R4 will pull the voltage up directly to the supply voltage. That is, vp is equal to the supply voltage whenever the constant current circuit is off, whether Q3 is on or off. Because the detection comparison voltage V2 is typically greater than 0 and less than the supply voltage, the U2 comparator outputs a high level. At the moment of conducting the constant current circuit, the gate voltage of the Q3 is delayed due to the existence of parasitic capacitance, and the gate of the Q3 is extremely high level to the source, and the high level can control the Q3 to keep an on state.
Because Q3 is opened, the internal resistance of Q3 is negligible or can be converted into a fixed resistance, and under the constant current state, vp is only related to the resistance of the heater. When the temperature of the heater is not high, the resistance of the heater is small, the resistance of the two ends of the heater is not high, and Vp is the power supply voltage minus the small voltage of the two ends of the heater. As the heater temperature increases, the heater resistance increases, the voltage across the heater increases, and Vp becomes smaller. When the heater resistance is greater than a certain value, vp is lower than V2 and the U2 output immediately goes low. In this case, Q3 is turned off, and since the constant current circuit itself is still in an on state, vp drops rapidly after Q3 is turned off, and the output of U2 remains unchanged. At this time, the circuit enters a steady state, and the power supply of the heater is cut off, thereby achieving the purpose of protecting the heater.
As described above, Q3 must be in an on state regardless of whether Q3 is on or not, as long as the constant current circuit is turned off and then turned on again. The reset of the protection switch can be realized by turning the constant current circuit off and then on again. After reset, if the heater temperature is lower than the protection temperature, the heater starts to work normally. If the temperature of the heater is higher than the protection temperature, the circuit rapidly enters the protection state again, and the power supply of the heater is cut off until the circuit is not reset.
V2 in the circuit can be calibrated according to actual conditions, for example, a sliding rheostat is used in a resistor voltage division mode, and the protection temperature of the heater is strictly limited to a certain temperature point.
If V2 is output by a digital-to-analog converter (DAC), the method can be used as a means for controlling temperature by matching with logic modification of a Micro Control Unit (MCU), and does not need participation of a temperature sensor. Referring specifically to fig. 4 and 5, fig. 4 schematically shows a schematic diagram of a non-self-healing over-temperature protection circuit according to one embodiment of the present application. In the schematic diagram shown in fig. 4, the principle of over-temperature protection is similar to the protection circuit shown in fig. 3, but with the addition of an external temperature control circuit. The external temperature control circuit can input a pulse width fixed modulation (PWM) signal to the constant current circuit, thereby controlling the on-off of the constant current circuit. In one embodiment, the external temperature control circuit may detect the temperature of the heater by a temperature sensor, and when the temperature of the heater falls within an acceptable temperature range, the heater is restarted.
Fig. 5 schematically illustrates a non-self-healing over-temperature protection circuit according to another embodiment of the present application. In the circuit shown in fig. 5, the control temperature is output to U2 through the DAC, when the temperature is too high, the voltage comparator U2 outputs an over-temperature output signal to the MCU, and after the MCU recognizes the signal, the circuit is reset through the control input terminal, and the heater resumes heating. When the heater has an over-temperature condition, the voltage comparator U2 continues to output an over-temperature signal, and the MCU resets and controls again. The resistance change signal comes from the heating material of the heater, and the temperature time delay is very low, so that the temperature controllability is better than that of a common heater, and a certain temperature control precision can be achieved without PID control.
If the over-temperature output and the control signal of the over-temperature protection circuit described in fig. 3 are logically changed, the MCU participating in the temperature control process may be omitted, and only the DAC output and the switching signal are needed. Referring specifically to fig. 6 and 7, fig. 6 schematically illustrates a schematic diagram of a temperature control circuit according to another embodiment of the present application. In the schematic circuit diagram shown in fig. 6, a control logic circuit is added at the front section of the constant current circuit, so that the over-temperature signal of the voltage detection comparison circuit and the control signal of the external start-stop circuit are simultaneously involved in controlling the on-off of the constant current circuit.
Fig. 7 schematically illustrates a temperature control circuit according to another embodiment of the present application. Compared with the non-self-recovery type over-temperature protection circuit shown in fig. 5, the temperature control circuit shown in fig. 7 inverts the over-temperature output of the output end of the voltage comparator in the voltage detection comparison circuit and switches the input phase to the output phase. When the switch input is closed, the circuit is in a reset state. After the switch is turned on, after the temperature of the heater rises to a certain temperature, the U2 outputs a low level, after the temperature is inverted by the U3A, the phase is input to the switch through the CMOS AND gate device U4 and the switch, the constant current circuit is controlled to be turned off, and the switch is reset. In one embodiment, U3 is CD40106. In one embodiment, U4 is 74HC08. After the switch works normally, the heater continues to heat. If the temperature exceeds the protection temperature, U2 immediately outputs an over-temperature signal, and the constant current circuit is turned off and reset. So as to achieve the effect that the temperature floats up and down at the temperature control point. The purpose of the schmitt trigger NOT gate adopted by U3 is to prevent insufficient temperature drop time in a period of time after triggering, and the temperature continues to rise and cannot be constant due to the fact that the temperature continues to be heated. If the triggering time is insufficient, a plurality of schmitt triggers can be added in series, and the speed of the change of the resistance-capacitance reduction signal can be increased in the schmitt triggers optionally so as to prevent the insufficient cooling time.
The circuits shown in fig. 5 and 7 do not need a temperature sensor to participate in temperature control, and do not need a temperature switch to participate, so that the size of the heater can be greatly reduced, and a single fault protection function is not lost. Provides a novel idea in the aspect of miniaturized heater, and has high practical value and economic value.
The embodiments are described above in order to facilitate the understanding and application of the present application by those of ordinary skill in the art. It will be apparent to those skilled in the art that various modifications can be made to these embodiments and that the general principles described herein may be applied to other embodiments without the use of inventive faculty. Accordingly, the present application is not limited to the embodiments herein, and those skilled in the art, based on the present disclosure, may make improvements and modifications without departing from the scope and spirit of the present application.
Claims (10)
1. An over-temperature protection circuit for a heater comprises the heater, a constant current circuit for supplying power to the heater, a voltage comparator, a protection switch and a first resistor, wherein the voltage comparator comprises a "+" end input end, a "-" end input end and an output end, and when the heater has an over-temperature condition, the output end of the voltage comparator outputs an over-temperature signal;
wherein the protection switch is connected in series with the heater;
wherein the first resistor is configured in parallel with the heater;
the "+" end input end of the voltage comparator is used for inputting the difference between the power supply voltage and the voltages at the two ends of the heater, and the "-" end input end of the voltage comparator is used for inputting the temperature protection point voltage; and
the output end of the voltage comparator is electrically communicated with the protection switch and is configured to turn off the protection switch when the output end of the voltage comparator outputs an over-temperature signal,
when the constant current circuit is closed, if the protection switch is opened, the protection switch and the heater can enable the input terminal voltage of the "+" terminal to be equal to the power supply voltage; if the protection switch is turned off, the first resistor directly pulls up the input end voltage of the "+" end to the power supply voltage, and the voltage comparator outputs a high level;
at the moment of conduction of the constant current circuit, the protection switch keeps on state due to the existence of parasitic capacitance, the internal resistance of the protection switch is negligible or can be converted into fixed resistance, under the constant current state, the voltage of the input end of the "+" end is only related to the resistance of the heater, when the temperature of the heater is low, the resistance of the heater is low, the voltage of the input end of the "+" end is the power supply voltage minus the small voltage of the two ends of the heater, the voltage of the two ends of the heater rises along with the rising of the temperature of the heater, the voltage of the input end of the "+" end is higher and lower, the voltage of the input end of the "+" end is lower than the temperature protection point voltage, the output of the voltage comparator immediately becomes low level, under the condition, the protection switch is cut off, the voltage of the input end of the "+" end is rapidly lowered after the constant current circuit is cut off, the output of the voltage comparator is kept unchanged, at the moment, the power supply of the heater enters steady state, and the power supply of the heater is cut off.
2. The over-temperature protection circuit for a heater according to claim 1, wherein the heater is a positive temperature coefficient heater.
3. The over-temperature protection circuit for a heater according to claim 1, wherein the protection switch is a CMOS device and/or a solid state relay.
4. The over-temperature protection circuit for a heater of claim 3, wherein the protection switch is a CMOS device, a gate of the CMOS device is in electrical communication with an output of the voltage comparator, and the over-temperature protection circuit for a heater further comprises a second resistor having one end in electrical communication with the gate of the CMOS device and the other end in electrical communication with the output of the voltage comparator.
5. The over-temperature protection circuit for a heater according to claim 1, further comprising a digital-to-analog converter, an external temperature control circuit, and a micro control unit;
the digital-analog converter is used for outputting temperature protection point voltage;
wherein the micro-control unit is configured to receive an over-temperature signal at the output of the voltage comparator and to provide an external temperature control input signal; and wherein the external temperature control circuit is configured to reset the protection switch.
6. The over-temperature protection circuit for a heater of claim 1, further comprising a digital-to-analog converter, an external start-stop circuit, and control logic;
the digital-analog converter is used for outputting temperature protection point voltage;
the external start-stop circuit is used for providing a fixed pulse width input signal, and the fixed pulse width input signal is used for controlling the on-off of the constant current circuit;
wherein the control logic circuit comprises a CMOS and gate device and at least one schmidt gate device in series, one end of the at least one schmidt gate device being in electrical communication with the output of the voltage comparator and the other end being in electrical communication with the input of the CMOS and gate device; and
wherein the fixed pulse width input signal is in electrical communication with an input of the CMOS and gate device and an output of the CMOS and gate device is in electrical communication with the constant current circuit.
7. The overheat protection circuit for a heater according to claim 1, wherein the output terminal of the voltage comparator outputs a low level as an overheat signal when an overheat condition occurs to the heater, and the protection switch is turned off.
8. The overheat protection circuit for a heater of claim 5, wherein when an overheat condition occurs in the heater, the output terminal of the voltage comparator outputs a low level as an overheat signal, the protection switch is opened, and the micro control unit re-closes the protection switch through the external temperature control circuit after receiving the overheat signal.
9. The overheat protection circuit for a heater of claim 5, wherein the output terminal of the voltage comparator outputs a low level as an overheat signal when an overheat condition occurs to the heater, the protection switch is opened, and the external temperature control circuit re-closes the protection switch when it is detected that the temperature of the heater falls below an acceptable maximum temperature.
10. The over-temperature protection circuit for a heater according to claim 5, wherein when an over-temperature condition occurs in the heater, the output terminal of the voltage comparator outputs a low level as an over-temperature signal, the protection switch is opened, the next fixed pulse width input signal provided by the external power-on/off circuit causes the constant current circuit to be electrically connected again, the protection switch to be closed again, and the heater to be started again.
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| Application Number | Priority Date | Filing Date | Title |
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| CN201810298704.XA CN108306258B (en) | 2018-04-04 | 2018-04-04 | Over-temperature detection circuit and over-temperature protection circuit for heater |
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| CN201810298704.XA CN108306258B (en) | 2018-04-04 | 2018-04-04 | Over-temperature detection circuit and over-temperature protection circuit for heater |
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| CN108306258A CN108306258A (en) | 2018-07-20 |
| CN108306258B true CN108306258B (en) | 2023-12-29 |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN109980599B (en) * | 2019-04-19 | 2021-04-13 | 中国电子科技集团公司第五十八研究所 | Over-temperature protection structure suitable for conventional CMOS (complementary metal oxide semiconductor) process |
| CN111934281B (en) * | 2020-08-10 | 2022-06-03 | 迈普通信技术股份有限公司 | Electronic equipment overtemperature protection circuit, electronic equipment and overtemperature protection control method |
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