JPS588650B2 - Ondokenshiyutsuniyorhogocairo - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to improving the stability of protection circuits through temperature sensing.

A protection circuit based on temperature detection that utilizes the temperature sensitivity of the transistor itself has conventionally been constructed as shown in the circuit shown in FIG.

In the figure, I is a constant current source, ZD is a Zener diode, Q1 is a transistor, and R1 and R2 are resistors connected in series and serve as the emitter resistance of the transistor Q1.

These I, ZD, Q1R1, and R2 constitute a constant voltage power supply 1 that outputs the voltage divided by R2.

Q2 is a particularly temperature-sensitive transistor, Vcc is a circuit power supply terminal, GND is a ground terminal, and OP is an output terminal of the protection circuit and is connected to the protected circuit.

This protection circuit converts the constant voltage made constant by the Zener diode ZD and divided by R1R2 into the base-emitter voltage VBEQ of the transistor Q2, which has a negative temperature coefficient.
2, the temperature is detected and the OP output at that time is used to protect the circuit by short-circuiting the input of the circuit to be protected. However, in conventional circuits like this, when the heat capacity of the circuit to be protected is small, etc. In some cases, as soon as the protection circuit is activated, the temperature of the protected circuit drops and the protection circuit returns to a non-activated state, causing the temperature of the protected circuit to rise again, causing oscillations of tens to hundreds of Hz. This also resulted in the equipment being destroyed.

The present invention aims to improve these drawbacks.

The details will be explained below. FIG. 2 is a circuit diagram of a first embodiment of the present invention.

In FIG. 2, the same functional parts as in FIG. 1 are given the same reference numerals.

In the circuit of FIG. 2, in addition to the circuit of FIG. 1, transistors Q3 and Q2, emitter resistors R4 and Q2 common to Q3,
Collector resistors R3 and R5 are provided for each Q3, so that the temperature detection circuit portion has a Schmitt trigger circuit 2 configuration.

The present invention has the above configuration, and the voltage across R4 differs by approximately R4·Vcc/R4+R5 between the conducting state and non-conducting state of Q2 due to temperature change.
3 ON, OFF, that is, between the operation and opening of the protection circuit =
(, d'B ''Q 7Q&・Vcc (R4+R6) There is a temperature hysteresis of dT, and by making this sufficiently large, oscillations like the conventional ones can be prevented and stable operation can be obtained. It has great effects.

[Brief explanation of the drawing]

FIG. 1 is a conventional protection circuit diagram using temperature detection, and FIG. 2 is a circuit diagram of a first embodiment of the present invention. Q2...1st stage transistor, 2...
・Schmitt trigger circuit, 1...constant voltage power supply, Q3...2nd stage transistor.

Claims (1)

[Claims] 1. The first stage transistor has a temperature-sensitive Schmitt trigger circuit and a constant voltage power supply that maintains the input terminal of the first stage transistor at a constant voltage, and is triggered by a temperature rise of the first stage transistor. A protection circuit using temperature detection, which is characterized by protecting a protected circuit using a second stage transistor output.