JPS6170808A - Thermal protection circuit - Google Patents

Abstract

PURPOSE:To minimize number of components and to reduce power consumption by connecting a current source of current mirror connection to the 1st current source of a reference voltage circuit via a diode and constituting the current of the current source to be switched. CONSTITUTION:Transistors (TR) Q1, Q2, Q3, Q4 and resistors R1, R2 constitute a band gap type reference voltage circuit. A reference voltage Vref is divided by resistors R3, R4 via an emitter follower TRQ6 and fed to a TRQ8 and an output TRQ9. The TRQ8 switches a collector current of a TRQ7 to switch the circuit current of a reference voltage circuit section through a TRQ5 of diode connection. When the relation of VB(OFF)>VB8((ON) is established at a high temperature (where VB(OFF) is a base voltage of the Q8 when the Q8 is turned off and VB8(ON) is a base voltage when the Q8 is turned on), the Q8 is turned on. In this case, since the current of the Q7 flows to the Q8, the base voltage of the Q8 is VB(ON) to attain the relation of VB(ON)>VB9(ON), an output TRQ9 is turned on to attain thermal protection.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention protects the circuit device by stopping the function of the circuit device, for example, when a semiconductor integrated circuit device generates heat or an abnormal temperature rises outside. This relates to a thermal protection circuit that can be used.

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, 6 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.

DESCRIPTION OF THE INVENTION The present invention provides a first . Of each of the second transistors, a resistor is connected to the collector of the second transistor, and the collector of the first transistor and the other end of the resistor are connected to the first . A second current source is connected, a third current source is coupled to the first current source via a diode, and the current of the third current source is switched. It is a thermal protection circuit that utilizes the voltage difference generated as hysteresis by switching the voltage generated across the resistor, and as a result, it is possible to reduce the number of circuit elements to a minimum. It is possible to realize a circuit with low power consumption by reducing the number of circuits.

DESCRIPTION OF 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.

Transistoro 1. Q2. Q3. Q4 resistors R1 and R2 constitute a reference voltage circuit called a bandgap type. This reference voltage vref is divided by resistors R3 and R4 via emitter follower transistor Q6, and is supplied to transistor Q8 and output transistor Q9. Transistor Q8 switches the collector current of transistor Q7, and switches the circuit current of the reference voltage circuit section through diode-connected transistor Q6.

When the transistor Q8 is in the OFF state, the base voltage VB (OFF) of the transistor Q8 is expressed by the following equation.

T: Junction temperature, "R2; ) Emitter current of transistor Q2, Eei) Emitter current of transistor Q6, R
1, R2, R3, R4, and the resistance values of the resistors R1, R2, R3, and R4. It is assumed that the characteristics of each transistor are the same and that the pace current can be ignored, and the emitter area of transistor Q is 02 times that of transistor Q2, and the same area of transistor Q4 is twice that of transistor Q3.

When the transistor Q8 is in the ON state, the pace voltage VB(ON) of the transistor Q8 is expressed by the following equation.

Next, the base voltages at which the transistor Q8 and the output transistor are turned on are set to vBa(ON) and VB9(O
N), it can be expressed by the following formula, where Is is the saturation current at reverse bias between the transistor's pace and emitter,
Engineering. ; Current drawn during thermal protection.

By appropriately selecting each resistance value and current value, VB (OFF) B (ON) <vBa (ON) ≦ vB
9(ON)<V, transistor Q8 becomes OFF state, and output transistor Q9 becomes OFF state.

〉■ Next, when the high temperature Kl), VB (OFF) and BS (ON) are reached, the transistor Q8 changes from the OFF state to the ON state. At this time, the current of transistor Q7 flows to transistor Q8, so the base voltage of transistor Q8 is V
It becomes B (ON). VB(ON)>VB9(ON)
The output transistor Q9 is turned on, and the thermal protection state is entered.

The junction temperature at which VB (OFF) ``va (ON)'' is determined is the thermal protection operating temperature ``C (ON)''.

Next, the temperature drops from the thermal protection state, and VB(ON)<vBe
(ON), transistor Q8 changes from ON state to OFF state.
FF state is entered, and the current of transistor Q7 is again
The voltage flows through the entire transistor Q7 to the reference voltage/circuit section. At this time, the pace of transistor Q8 is VB(OF
F) K becomes s vB(OFF)" Since BS(ON), the output transistor Q9 becomes OFF state and thermal protection is released. The junction temperature where v=v B(ON) Bs(ON) is Set the protection release temperature to “C” (OFF).

TO(ON)t C(OFF) is approximately (four holes, (
Represented by the @ expression.

.....
(OFF) is the pace-emitter voltage of the transistor Q8 at each junction temperature of TC(ON) and C(OFF).

In addition, in the embodiment circuit diagram of FIG. 2, the starting circuit is omitted. Furthermore, as is clear from the conventional circuit shown in FIG. 1, the circuit shown in FIG. 2 does not require a hysteresis comparator and can simplify the circuit configuration.

Effects of the Invention The circuit configuration of the present invention eliminates the hysteresis comparator, significantly reduces power consumption, reduces the number of circuit elements, and greatly reduces chip area, and is suitable for semiconductor integrated circuits.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a conventional example, and FIG. 2 is a circuit diagram of an embodiment of the present invention. Q1-Q9...Transistor, R1-R4...
····resistance. Name of agent: Patent attorney Toshio Nakao and 1 other person 2nd
figure

Claims (1)

[Claims] A resistor is connected to the collector of the second transistor among the first and second transistors of the current mirror pair that operate at different current densities, and a resistor is connected to the collector of the first transistor and the other end of the resistor, respectively. The first and second current sources of the current mirror circuit are connected, and a third current source that is coupled to the current mirror circuit is coupled to the first current source via a diode. Thermal protection circuit includes a third transistor capable of switching the current of the circuit.