JPS6170805A - Thermal protection circuit - Google Patents

Abstract

PURPOSE:To realize a low power consumption circuit with a minimum circuit element number by using an input transistor (TR) of a hysteresis comparator to a temperature detection section. CONSTITUTION:An output voltage of a reference voltage circuit 7 of the band gap system is divided by resistors R4 and R5 via an emitter follower TRQ4 and fed to an input TRQ5 of a current source CC2 load of the hysteresis comparator. Further, the output of the comparator is fed to an output TRQ8 through a circuit comprising a current source CC3, a TRQ6 and a common emitter resistor via a circuit comprising an emitter follower TRQ7 and resistors R7, R8. When the TRQ5 is turned off at a low temperature, the relation of VB>VB5(ON) is established (where; VB is base voltage and VB5(ON) is a base voltage to turn on the Q5 from the off-state), the Q5 is turned on to attain thermal protection state. When the temperature decreases and the relation of VB5<VB5(OFF) is established, the Q5 is turned off to release the thermal protection.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a thermal protection circuit that can stop the function of the circuit device and remove the circuit device in the event of an abnormal rise in external temperature.

Conventional configuration and its problems A thermal protection circuit usually includes a reference voltage circuit, a temperature detection device, and a hysteresis comparator. FIG. 1 is a conventional circuit diagram of this type. In the figure, 1 is a reference voltage circuit, 2 is a temperature detection device, 3 is a hysteresis comparator, 4 is an output circuit, 5 is a power supply voltage terminal, and 6 is an output terminal.

This circuit configuration has disadvantages such as a large number of elements, large current consumption, and a large chip area.

OBJECTS OF THE INVENTION The present invention provides a thermal protection circuit that can minimize the number of circuit elements and reduce power consumption.

Structure of the Invention To summarize, the present invention is a thermal protection circuit using an input transistor of a hysteresis comparator in a temperature detection section,
Thereby, a circuit with low power consumption can be realized with a minimum number of circuit elements.

DESCRIPTION OF THE EMBODIMENTS FIG. 2 is a circuit diagram of an embodiment of the present invention, and the present invention will be described in detail with reference to this embodiment.

T is a known bandgap reference voltage circuit composed of transistors Q1 to Q5, resistors R4 to R3, and current source CC1, and its output voltage is divided by resistor R4 and resistor R5 via emitter follower transistor Q4. ,
The current source CC2 of the hysteresis comparator 8 is supplied to the input transistor Q5 of the load. Furthermore, the output of the hysteresis comparator 8 is the current source CG, the transistor Q
6 and a common emitter current is supplied to the output transistor Q8 through the circuit of emitter follower transistor Q7 and resistor R71R8.

Here, the reference voltage V generated by the band gap type reference voltage circuit 7 is approximately expressed by the following equation.

vBK5: Base-emitter voltage of Q5.

k: Boltzmann constant, T: junction temperature, q: electron charge
I, R2, R5'Resistor R4 and R2 and R5'
5 each resistance value. It is assumed that the characteristics of each transistor are the same, and that the base current can be ignored. The reference voltage V is divided by the transistor Q4 and the resistors R4 and R5, and is supplied to the base of the transistor Q5. The base voltage vB can be expressed by the following equation.

However, V□4: voltage between the base and emitter of transistor Q4, R4, R5: resistance values of resistors R4 and R5.

From the above equations 1 and 2, we obtain the following equation.

However, 3: Emitter current of transistor Q3.

This is actually the emitter current of transistor Q4.

In the above three equations, if each resistance value is selected appropriately, the transistor Q
The base voltage V of 5 is proportional to the junction temperature T.

Next, to explain the hysteresis comparator 8, the base voltage vas (...) required for the transistor Q5 to change from the OFF state to the ON state.

can be expressed by the following formula.

However, vBK5(oll,: transistor Q5 is ON
Base-emitter voltage at which the state occurs, X2: Current source C
Current value of C2, I: Current value of current source CO3, R6: Resistance value of resistor R6, I: Saturation current during reverse bias between the base and emitter of transistor Q5. Voltage v86. required for transistor Q5 to change from ON state to OFF state. . ,. can be expressed by the following formula.

Here, if the values of resistance and current are appropriately selected so that transistor Q5 is in the OFF state at low temperatures, then at high temperatures vII>vB5 (..., and transistor Q5 is OFF.
It changes from the F state to the ON state and enters the thermal protection state. VB=
The junction temperature of v85(., is the thermal protection operating temperature Tc(o
, l).

Next, the temperature drops from the thermal protection state, and vB<vB5(OF).

Then, the transistor Q5 changes from the ON state to the OFF state, and the thermal protection is released. VB=v85(OF.

The junction temperature becomes the thermal protection release temperature T0. . FF).

This thermal protection operating temperature T and thermal protection release temperature 0 (ON
) To,. 2. ) are the resistance and current values that can be set to the desired temperature.

As is clear from the circuit configuration of the embodiment shown in FIG. 2, the temperature detection device 2 is not required as compared with the conventional circuit shown in FIG. There is.

Effects of the Invention According to the circuit configuration of the present invention, as is clear from a comparison with conventional circuits, a temperature detection device is not required, which reduces power consumption and the number of circuit elements, making it possible to improve semiconductor integrated circuits. suitable.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram of a conventional thermal protection circuit, and Fig. 2 is a circuit diagram of an embodiment of the present invention.
......Resistance CC, ~CC3... Constant current source. 1... Reference voltage circuit, 2... Temperature detection device, 3... Hysteresis comparator, 4...
...Output circuit, 5...Power supply voltage terminal, 6
... Output terminal, 7. Old bandgap method reference voltage circuit, 8. Hysteresis comparator. Name of representative: Patent attorney Toshio Nakao (1st person)
Figure 2

Claims (1)

[Claims] 1. A thermal protection circuit comprising a bandgap type reference voltage circuit and a hysteresis comparator circuit, and using an input transistor of the hysteresis comparator circuit.