JPH0588142U - Electronic device protection circuit - Google Patents

Abstract

(57) [Summary] [Purpose] To detect the temperature difference at a predetermined location of an electronic device with high accuracy and set the operation start temperature of the protection circuit. [Structure] A reference contact 1 of a thermocouple is attached to a reference location of an electronic device, and a temperature measuring contact 2 is attached to an abnormal temperature detection location. Thermoelectromotive force e based on the temperature difference between the reference point and the detection point
1 is amplified by the offset voltage amplifier 3.
When the voltage e2 of the output of the voltage amplifier 3 exceeds the reference voltage E2 corresponding to the preset temperature difference, the comparator 5 outputs the control voltage e3 to control the relay drive unit 6 to cut off the power supply of the electronic device.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a protection circuit for an electronic device, and more particularly to a protection circuit for an electronic device that detects an abnormal temperature of the electronic device and shuts off the power supply.

[0002]

[Prior Art]

 In some electronic devices, a temperature sensor is built in, and an abnormality in the operation of the electronic device is determined based on the temperature detected by the sensor, and when there is an abnormality, the power is cut off. The purpose of this protection circuit is to detect abnormal operation of the electronic device by temperature rise, cut off the power supply to minimize damage to the device and save repair cost. The purpose is to prevent fatal disasters such as smoke and fire. As a simple conventional protection circuit, there is one that detects the absolute temperature at a specified location with a thermistor and drives the relay etc. to shut off the power supply when the temperature exceeds a predetermined temperature. However, if it is assumed that the operating room temperature range of the device is set to -10 ° C to 40 ° C, the temperature rise during steady use is set to 20 ° C, and the abnormality determination temperature is further set to + 20 ° C, the set temperature is an absolute temperature. It becomes 80 ° C. That is, when the indoor temperature is used at -10 ° C, the protection circuit is activated when the temperature rises by 90 ° C, which is not suitable for the purpose of minimizing damage. Next, as a solution to the above problems, there is a method in which a reference point is provided in the device, a temperature difference from the reference point is detected, and when a preset temperature difference is reached, the protection circuit is activated. In this method, fluctuations in the room temperature used are removed, and the abnormality detection capability is greatly improved. However, when a thermistor or the like is used as the temperature sensor, the resistance-temperature characteristic of the thermistor is a logarithmic characteristic, and the value of the resistance change corresponding to the temperature difference varies depending on the indoor temperature. The correction using a correction amplifier or the like complicates the correction circuit, and it is a difficult task to check the correction results for each product. As a result, there is a margin in setting the temperature at which the protection circuit starts operating, to prepare for a malfunction of the protection circuit, which is a problem in accurately detecting an abnormality in the device and protecting the electronic device.

[0003]

[Problems to be solved by the device]

 The present invention has been made in view of such a point, and accurately detects the temperature difference between two locations in the electronic device to accurately detect the degree of abnormality in the entire range of the indoor temperature used. It is intended to provide a protection circuit for an electronic device that makes a determination and shuts off the power supply based on the determination result.

[0004]

[Means for Solving the Problems]

 In order to solve the above problems, the present invention measures a temperature difference at a predetermined location of an electronic device, detects that the temperature difference exceeds a predetermined temperature difference, and shuts off the power supply to protect the electronic device. A thermocouple that detects the temperature difference, an offset-adjustable voltage amplifier that amplifies a thermoelectromotive force corresponding to the temperature difference of the thermocouple, and a reference voltage that corresponds to the predetermined temperature difference. It is intended to provide a protection circuit for an electronic device, which is provided with a comparator that determines a value of an output voltage of a voltage amplifier and outputs a control signal.

[0005]

[Action]

 With the above configuration, in the protection circuit for the electronic device according to the present invention, the temperature difference between two predetermined locations inside the device is detected by the thermocouple, and the temperature difference corresponding to the temperature difference output by the thermocouple is detected. The thermoelectromotive force is amplified and output to the comparator. The comparator discriminates the input voltage from the reference voltage corresponding to the preset temperature difference, and outputs a control signal when the reference voltage is exceeded.

[0006]

【Example】

 Hereinafter, embodiments of a protection circuit for an electronic device according to the present invention will be described with reference to the drawings. FIG. 1 is a circuit diagram of an essential part showing an embodiment of a protection circuit for an electronic device according to the present invention. In the figure, reference numeral 1 is a reference junction of a thermocouple attached to a reference point in the device, and 2 is a temperature measurement junction of a thermocouple attached to a measurement point, which corresponds to a temperature difference between the reference point and the measurement point. Is output. Reference numeral 3 denotes a voltage amplifier which receives the thermoelectromotive force e1 and the offset voltage E1 as inputs, and outputs a voltage e2 obtained by predetermined amplification. The resistor R1 is an input resistor and the resistor R2 is a feedback resistor, which determines the gain of the voltage amplifier 3. Reference numeral 4 is an offset voltage generating circuit, which is composed of a variable resistor VR1, supply voltages + Vcc, -Vcc, etc., and generates and outputs an adjustable offset voltage E1. Reference numeral 5 denotes a comparator, which compares the voltage e 2 output from the voltage amplifier 3 with the reference voltage E 2 to output a control voltage e3. The resistor R3 and the variable resistor VR2 divide the supply voltage + Vcc to generate a reference voltage E2 and supply it to the comparator 5. Reference numeral 6 denotes a relay drive unit, which controls the power supply unit of the device based on the control voltage e3 to protect the electronic device.

Next, the operation of the protection circuit of the electronic device according to the present invention will be described. The reference contact 1 of the thermocouple is mounted at a place that does not cause a temperature rise due to an abnormal operation, which represents a normal temperature rise of the electronic device. The temperature measuring contact 2 of the thermocouple is mounted at a location where a corresponding temperature rise occurs if an abnormality occurs. Now, the case of using the iron-constantan thermocouple will be described. In this case, in the target temperature range, the thermoelectromotive force-temperature characteristic is almost linear, and about 53 μV / ° C is obtained. Therefore, if the temperature of the reference contact 1 of the thermocouple is T1 and the temperature of the temperature measuring contact 2 is T2, the thermoelectromotive force is e1≅53 (T2-T1) μV. The output voltage of the voltage amplifier 3 becomes e2≅53 (T2-T1) R2 / R1 μV, which is output to the comparator 5. At this time, the offset voltage E1 is adjusted by the variable resistor VR1 such that the output voltage e2 becomes zero when the input voltage e1 is zero. Next, the reference voltage E2 of the comparator 5 becomes E2≅53T3R2 / R1 μV when the value of the temperature difference for shutting off the power source is set to T3, and is given by adjusting the variable resistor VR2. When e2> E2, that is, T2-T1> T3, the comparator 5 outputs the voltage e3 to drive the relay drive circuit 6 to cut off the power supply.

Next, there is a case where there is a considerable temperature difference between the temperature of the reference contact 1 and the temperature of the temperature measurement contact 2 in the steady operation state. In such a case, the thermoelectromotive force corresponding to this temperature difference can be offset by the offset voltage E1, and the output voltage e2 of the voltage amplifier 3 in the steady operation state can be made zero. Then, the output voltage e2 of the voltage amplifier 3 can obtain a voltage corresponding to only the temperature increase due to the abnormality, so that the temperature difference for abnormality determination can be set with higher accuracy.

When a copper-constantan thermocouple is used, the influence of nonlinearity due to the square characteristic of the thermoelectromotive force-temperature characteristic appears as an error in the target temperature range. In this case, the linearity may be corrected by a logarithmic amplifier or the like for use as described above, or the temperature may be set in consideration of an error. Even if it is used without correction, the temperature difference can be detected with high accuracy in comparison with the non-linearity of the thermistor and the variation of characteristic constants.

[0010]

[Effect of the device]

 As described above, in the protection circuit for the electronic device according to the present invention, the temperature difference between the reference point and the measurement point in the device is detected by the thermocouple, and the detection circuit drives the relay of the protection circuit. .. Therefore, it is possible to detect the temperature rise of the target location with high accuracy, and it is possible to protect the electronic device by detecting the occurrence of a malfunction in the initial stage. Furthermore, the reliability of the protection circuit can be further enhanced by offsetting the temperature difference between the reference point and the measurement point in the steady operation state and setting the operating temperature.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an essential part showing an embodiment of a protection circuit for an electronic device according to the present invention.

[Explanation of symbols]

 1 Thermocouple reference junction 2 Thermocouple temperature measuring junction 3 Voltage amplifier 4 Offset voltage generator 5 Comparator 6 Relay driver R1 Input resistance R2 Feedback resistance R3 Resistance VR1 Variable resistor VR2 Variable resistor

Claims (2)

[Scope of utility model registration request] 1. A temperature difference at a predetermined location of an electronic device is measured,
A protective circuit for an electronic device, which detects that a temperature difference exceeds a predetermined temperature difference and shuts off the power supply, and a thermocouple for detecting the temperature difference and a thermocouple corresponding to the temperature difference between the thermocouples. An offset adjustable voltage amplifier for amplifying electric power, and a comparator for determining a value of an output voltage of the voltage amplifier based on a reference voltage corresponding to the predetermined temperature difference and outputting a control signal. A protection circuit for an electronic device. 2. The protection circuit for an electronic device according to claim 1, wherein the predetermined temperature difference is set by offsetting the temperature difference at the predetermined location in the steady operation state by the voltage amplifier.