JP2002245914A - Circuit protective device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a power from being fed while repeating abnormality many times by completely interrupting a power supply to an electric circuit without using a temperature fuse. SOLUTION: When the part or circuit of an electric circuit 1 causes an abnormality such as a trouble to abnormally raise a temperature inside the electric circuit 1, the abnormal temperature inside the electric circuit 1 is detected by a temperature detection means 4. The transistor Q3 is turned on by an output from the temperature detection means 4. Since an excessive current flows through a fuse F2 when the transistor Q3 is turned on, the fuse F2 is blown off. When the fuse F2 is blown off, a voltage across the gate sources of a MOSFET Q4 is always lower than a threshold voltage. The MOSFET Q4 is turned off permanently to stop supplying power to the electric circuit 1 so as to safely protect the electric circuit 1.

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 detecting an abnormal temperature and protecting an electric circuit.

[0002]

2. Description of the Related Art A conventional circuit protection device of this type is configured as shown in FIG. As shown in FIG. 2, a temperature fuse F1 is used between one end of the input terminal 3 connected to the electric circuit 1 and the electric circuit 1. At this time, the temperature fuse F1 is mounted in close contact with a temperature detecting portion such as a main element of the electric circuit 1 which requires temperature detection. With this arrangement, when the temperature detection portion exceeds the set temperature, the input of power supply from the input terminal 3 of the electric circuit 1 is cut off by cutting the temperature fuse F1.

As another example, as shown in FIG. 3, a transistor Q1 is connected between one end of an input terminal 3 connected to the electric circuit 1 and the electric circuit 1, and a base of the transistor Q1 is connected to the electric circuit. Between the other end of the input terminal 3 connected to the circuit 1, a resistor R1 and a transistor Q2 are connected in series. Further, the base of the transistor Q2 and the temperature detecting means 4 provided in the electric circuit 1 are connected.

When the temperature detecting means 4 detects an abnormal temperature such as overheating in the electric circuit 1, the transistor Q2 is turned off.
F, whereby the transistor Q1 is turned off to cut off the power supply from the input terminal 3 to the electric circuit 1, thereby protecting the electric circuit 1.

[0005]

However, the conventional thermal fuse used in the circuit protection device having such a configuration is expensive and the thermal fuse is cut at the soldering temperature at the time of mounting. There was a problem.

Further, in the case of the conventional circuit protection device shown in FIG. 3, when the state returns from the overheated state to the normal state, the transistor is turned on and the power supply to the electric circuit is restarted. When the electric circuit is abnormal due to the power supply, the electric circuit is overheated again, and there is a problem that the electric circuit is fundamentally destroyed.

SUMMARY OF THE INVENTION The present invention is directed to solving the above-mentioned problems of the prior art, and does not use a thermal fuse that may cut the thermal fuse depending on the temperature at the time of mounting by soldering. An object of the present invention is to provide a circuit protection device that completely cuts off power supply to a circuit, prevents power supply from repeating an abnormal state many times, and does not completely destroy an electric circuit.

[0008]

To achieve this object, a circuit protection device according to the present invention comprises a first transistor provided between one end of an input terminal connected to an electric circuit and the electric circuit. , A first transistor connected in series between the base of the first transistor and the other end of the input terminal connected to the electric circuit.
, A second resistor and a second transistor connected in parallel between a connection end of the first resistor and the fuse and one end of the input terminal, and a base of the second transistor. A temperature detecting means provided in the electric circuit, wherein an overcurrent is supplied to the fuse by the abnormal temperature detection of the temperature detecting means to cut the fuse.

Further, the first transistor is MOSF
ET.

According to these configurations, when an abnormal temperature is detected by the temperature detecting means, an overcurrent is applied to the fuse to cut the fuse, thereby completely cutting off the power supply to the electric circuit, and repeating the abnormal state many times. Power supply to the electric circuit can be prevented, and power loss can be further reduced by using a MOSFET instead of a transistor.

[0011]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 shows a configuration of a circuit protection device according to an embodiment of the present invention. As shown in FIG.
One end of the input terminal 3 connected to the electric circuit 1 and the electric circuit 1
, And a resistor R2 and a fuse F2 are connected in series between the gate of the MOSFET Q4 and the other end of the input terminal 3 connected to the electric circuit 1.

A resistor R3 and a transistor Q3 are connected in parallel between a connection end of the resistor R2 and the fuse F2 and the other end of the input terminal 3 connected to the electric circuit 1,
Further, the base of the transistor Q3 is connected to the temperature detecting means 4 provided in the electric circuit 1.

The operation of the present embodiment configured as described above will be described with reference to FIG. Now, when an abnormality such as a failure occurs in a component or a circuit of the electric circuit 1 and the temperature in the electric circuit 1 rises abnormally, the abnormal temperature in the electric circuit 1 is detected by the temperature detecting means 4. The transistor Q3 is turned on by the output from the temperature detecting means 4. When the transistor Q3 is turned on, an excessive current flows through the fuse F2, so that the fuse F2 is cut.

When the fuse F2 is cut, the voltage between the gate and the source of the MOSFET Q4 always becomes lower than the threshold voltage.
Since the switch 4 is permanently OFF, power is not supplied to the electric circuit 1, and the electric circuit 1 can be protected safely.

[0016]

As described above, according to the present invention,
There is no need to use an expensive thermal fuse that may blow the thermal fuse due to the soldering temperature at the time of installation, and if an abnormal temperature rise in the electric circuit is detected, an excessive current will flow through the fuse to cut the fuse. MOSFE
By always turning T off, once the abnormal temperature rise of the electric circuit is detected once, the power supply to the electric circuit is completely cut off, preventing the electric circuit from being completely destroyed by repeating the abnormal state many times. The use of MOSFETs has the effect of reducing power loss.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a circuit protection device according to an embodiment of the present invention.

FIG. 2 is a diagram showing a configuration of a conventional circuit protection device.

FIG. 3 is a diagram showing another configuration of a conventional circuit protection device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Electric circuit 3 Input terminal 4 Temperature detection means Q1, Q2, Q3 Transistor Q4 MOSFET F1 Temperature fuse F2 Fuse R1, R2, R3 Resistance

Claims (2)

[Claims] A first transistor provided between one end of an input terminal connected to an electric circuit and the electric circuit; a base of the first transistor; and an input terminal connected to the electric circuit. A first resistor and a fuse connected in series between the first terminal and the second terminal connected in parallel between a connection end of the first resistor and the fuse and one end of the input terminal;
A resistor and a second transistor, and a temperature detecting means provided in the electric circuit connected to a base of the second transistor, and an overcurrent is supplied to the fuse by detecting an abnormal temperature of the temperature detecting means. A circuit protection device, wherein the fuse is cut by a fuse. 2. The method according to claim 1, wherein the first transistor is a MOSFET.
The circuit protection device according to claim 1, wherein: