JPH04340320A - circuit protection device - Google Patents

Abstract

PURPOSE:To protect equipment by breaking a driving power supply circuit to a part at abnormal overheating of the same part. CONSTITUTION:A part 4 is supplied with driving power through the switching circuit by a transistor 2, and reference voltage V2 is input into by comparison circuit by a comparator 5, and Vcc is connected to earth by a resistor R1 and a thermistor Rt arranged in series. With the thermistor Rt side as an earth, the said power voltage is divided, and the same divided voltage V1 is input as comparison voltage, and the thermistor Rt is attached to the inside, etc., of the part 4, and the abnormal temperature rise of the part 4 is detected as the change of the resistance value of the thermistor Rt. A comparator 5 compares the comparison voltage V1 generated by the change of the same voltage value and the reference voltage V2 and outputs a control signal, and input, it into said switching circus, and breaks the same switching circuit to stop the power supply to the part 4 and protect equipment.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a circuit protection device for protecting equipment by cutting off a power supply circuit for driving the component when the component overheats abnormally. The occurrence of smoke or burnout accidents in electrical equipment is related to the magnitude of the current used in the equipment's circuit, the height of the energizing voltage, and the magnitude of the supplied power.Television receivers in particular are particularly sensitive to these three values. Because it is large enough to cause an electrical fire, it is designated as a Class A electrical appliance under the Electrical Appliance and Materials Control Law, which causes many accidents. In Japan, when parts used in equipment are made flame-retardant, they are often incinerated when disposed of, and when incinerated, the flame retardant used to make the parts flame-retardant generates toxic gas, which may cause pollution. Therefore, if a large number of safety devices are installed in an aircraft, the safety devices may malfunction and break down due to changes over time or variations, reducing the reliability of the equipment. Therefore, the question is how to incorporate appropriate safety devices into equipment to ensure the safety of the equipment.

0002

2. Description of the Related Art Conventionally, electrical equipment has been protected by using fuses in power supply circuits, fuse resistors in electronic circuits, or thermal fuses in transformers, either singly or in combination. However, fuses and fuse resistors usually need to be loaded with a margin for the rating, and there is a region in which they do not blow when the current exceeds the rating, so there is a difference between normal operation and abnormal operation. Thermal fuses cannot be used as a safety device unless the current difference between them exceeds a certain level, and thermal fuses are difficult to use because they must be inserted directly into the internal circuit of the component.

0003

[Problem to be solved by the invention] Therefore, even when there is no difference in current between normal operation and abnormality, it is possible to detect an abnormal temperature rise occurring in a component, detect a failure of the device, and supply power to the component. An object of the present invention is to provide a circuit protection device that can protect electrical equipment by interrupting a circuit.

0004

[Means for Solving the Problems] FIG. 1 is an electrical circuit diagram of a circuit protection device showing one embodiment of the present invention. a circuit that supplies driving power to the circuit, a circuit that inputs the reference voltage V2 to a comparison circuit using a comparator 5, and a resistor R1 and thermistor R that connect the power supply voltage in series.
t, the thermistor Rt side is connected to the ground, the thermistor Rt side is grounded, the power supply voltage is divided, and the divided voltage V1 is inputted to the comparator 5 as a comparison voltage. The comparator 5 detects the abnormal temperature rise of the component 4 as a change in the resistance value of the thermistor Rt, and the comparator 5 detects the comparison voltage V1 and the reference voltage V2 generated by the change in the resistance value. A control signal is output and inputted to the switching circuit to shut off the switching circuit, thereby stopping power supply to the component 4 and protecting the circuit.

[0005]

[Operation] With the above-described configuration, the present invention uses the thermistor Rt to detect an abnormal temperature rise that occurs when a component fails, and shuts off the power supply circuit to the component. There is almost no difference in the current flowing through the circuit, so even if protective devices such as fuses and fuse resistors cannot be used, abnormal operation of the circuit can be detected and equipment can be protected. Instead of directly inserting it into the internal circuit of a component and opening the internal circuit of the component due to an abnormal temperature rise of the component,
When attaching a thermistor Rt to a component, in order to ensure that the temperature rise of the component is well transmitted to the thermistor Rt, for example, the thermistor Rt is fixed to the surface of the component, or when attached to a high voltage unit of a television, the component is Thermistor Rt can be buried in a filler inside the case, or wrapped between insulating paper when incorporated into a transformer. It is possible to protect the equipment by detecting this and cutting off the power supply to the component.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is an electrical circuit diagram of a circuit protection device showing an embodiment of the present invention. Reference numeral 1 designates an input terminal to which a voltage of Vcc is inputted as a power source for driving a component 4. In FIG. The drive power supply circuit applied through the input terminal 1 is input to the collector of an NPN transistor 2 used as a switching circuit, and the emitter of the transistor 2 and the drive power input circuit of the component 4 are connected. A resistor R4 and a resistor R5 are connected to each other and the driving power supply Vcc is connected in series.
Connect to the ground through the resistor R5 side, divide the voltage of Vcc with the resistor R5 side as the ground, and use the divided voltage as the reference voltage V2.
is input to a comparison circuit using a comparator 5, and connected to the ground via a resistor R1 and thermistor Rt connected with the drive power supply Vcc in series, and divides the voltage of Vcc by setting the thermistor Rt side to the ground. The resulting voltage is input to a comparator 5 as a comparison voltage V1, and the control signal output terminal of the comparator 5 is input to the base of the transistor 2 via the bias resistor 3.

FIG. 2 is a resistance/temperature characteristic diagram of the thermistor Rt. As shown in the figure, a negative characteristic thermistor whose resistance value decreases as the temperature rises is used, and the resistor R1 and thermistor Rt During normal operation, comparator 5 outputs a control signal of H level with V1>V2, and outputs a control signal of H level from comparator 5 to compare voltage V1, which is Vcc divided by resistor R4 and resistor R5, and reference voltage V2, which is Vcc divided by resistor R4 and resistor R5. The voltage Vcc is inputted to the base of the transistor 2 via the bias resistor 3, and the drive power supply Vcc is supplied to the component 4 with the transistor 2 in a conductive state. The thermistor Rt is attached to the component 4, and the temperature of the thermistor Rt increases due to the abnormal temperature rise that occurs when component 4 fails, and the resistance value decreases as the temperature rises, so the comparison voltage V1 decreases, and V1<V2 When the state is reached, the control signal from the comparator 5 becomes L level, so no bias is applied to the base of the transistor 2, so the transistor 2 is cut off and the supply of driving power Vcc to the component 4 is stopped.
The circuit operation inside the component 4 is stopped to protect the electrical equipment.

By adjusting the reference voltage V2, it is possible to set the temperature at which the power supply to the component 4 is stopped, and by using a positive characteristic thermistor for the thermistor Rt, the comparison voltage input to the comparator 5 can be adjusted. V1 and reference voltage V
The two input pins may be exchanged and used. When using the thermistor Rt by attaching it to a high-voltage unit of a television, for example, insert a noise removal capacitor 6 between the dividing point where the power supply voltage Vcc is divided by the resistor R1 and thermistor Rt and the earth, and connect the thermistor Rt and the thermistor Rt. The voltage induced in the connection lead to Rt may be prevented from being applied to the comparator circuit 5. Similarly, a noise removal capacitor 7 is inserted between the dividing point where the power supply voltage Vcc is divided by the resistor R4 and the resistor R5 and the ground to prevent noise from being superimposed on the reference voltage V2 of the comparator circuit 5. Also good. Further, a plurality of thermistors Rt are used for the component 4 and attached to each part of the component 4, and the comparator circuit 5 detects a decrease in the comparison voltage V1 due to a decrease in the resistance value of at least one of the thermistors Rt. The electric equipment may be protected by stopping the supply of driving power Vcc to the electric equipment.

[0009]

[Effects of the Invention] As explained above, according to the present invention, an abnormal temperature rise occurring in a component can be detected even when there is no difference in the current flowing through the circuit between the normal operation of the component and the abnormal state caused by a failure. , provides an effective circuit protection device for electrical equipment that can protect electrical equipment by cutting off the power supply circuit to the parts, and also allows setting of a protection temperature that cuts off the power supply circuit to the parts. can do.

[Brief explanation of drawings]

FIG. 1 is an electrical circuit diagram of a circuit protection device showing one embodiment of the present invention.

FIG. 2 is a resistance/temperature characteristic diagram of the thermistor shown in FIG. 1.

[Explanation of symbols]

1 Input terminal 2 Transistor 3 Resistor 4 Parts 5 Comparator 6 Capacitor 7 Capacitor Rt resistor R1 Resistor R4 Resistor R5 Resistor

Claims (3)

[Claims] [Claim 1] A circuit for supplying driving power to components through a switching circuit, a circuit for inputting a reference voltage to a comparator circuit, and a power supply voltage connected to earth through a resistor and a thermistor connected in series, It consists of a circuit that divides the power supply voltage with the thermistor side grounded and inputs the divided voltage to the comparison circuit as a comparison voltage, and the thermistor is attached inside or on the outer periphery of the component, An abnormal temperature rise is detected as a change in the resistance value of the thermistor, and the comparison circuit compares the comparison voltage generated due to the change in the resistance value with the reference voltage to output a control signal and input it to the switching circuit. , a circuit protection device that protects the circuit by blocking the switching circuit and stopping power supply to the component. 2. The switching circuit uses a transistor, the collector inputs the driving power supply, the emitter is connected to an input circuit of the driving power supply for the component, and the base is connected to the transistor through a bias resistor. 2. The circuit protection device according to claim 1, further comprising a circuit connected to a control signal output terminal of the comparison circuit. 3. A noise eliminating capacitor is inserted between a dividing point where the power supply voltage is divided by the resistor and the thermistor and the ground to prevent noise from being superimposed on the comparison voltage. 1. The circuit protection device according to 1.