JPS63102248A - Overheat protection circuit - Google Patents

Abstract

PURPOSE:To make the setting of an operation temperature easy, and make the dispersion width of set temperature narrow, by a method wherein a constant current circuit is always normally operated by making a PNP transistor absorb the excess current of the constant current circuit before reaching an operation set temperature, and making it flow into a by-pass. CONSTITUTION:A temperature detection circuit comprises transistors Q5, Q6 and Q10, and resistors R5-R7, and drives transistors Q7 and Q8 which constitute a control circuit. Until P-N junction temperature reaches the operation set temperature of an overheat protection circuit the emitter current of the PNP transistor Q10 is a residual which results from ion of deduction of the collector current of the PNP transistor Q6 from that of PNP transistor Q5. At the operation time of overheat protection circuit, that is, the time when the PNP transistor Q7 operates, the emitter current of the transistor Q7 is supplied from the current flowing through the PNP transistor Q10, and the PNP transistor Q5 is not saturated. Accordingly, the constant current circuit normally operates all the time.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to integrated circuits, and more particularly to an overtemperature protection circuit that prevents the P-N junction of an integrated circuit from being destroyed due to an increase in the temperature of the P-N junction. .

BACKGROUND ART FIG. 1 is a circuit diagram showing an example of a conventional overheat protection circuit. 2 in FIG. 2, this overheating protection circuit has a power supply terminal a, an output terminal b1, and a ground terminal C. The power supply terminal a is connected to the anode side of a constant voltage diode Qv via a resistor R1, while the constant voltage Diode Q? The cathode side of is connected to ground terminal C, and resistor R1 and constant voltage diode Q9
The intersection of the anodes of is connected to the base of NPN ) transistor Q through resistor R, and
The bases of resistors R and PNP) are connected to the collector of transistor Q3, the emitter of NPN) transistor Q41 is connected to the ground terminal ck, and the NPN) transistor Q2 is connected to the base of
The emitter of is connected to the ground terminal via resistor R3, and N
PN) The collector of transistor Q is connected to the collector of transistor Q, < all connected points,
The base of the PNP) transistor Q3°Qt is connected to the connection point of the collector base of the PNP) transistor Q/, and the emitters of the PNP) transistor Q'+Q3-Q3 are each connected to the power supply terminal a. A reference voltage circuit including such a constant current circuit, and a resistor Ra and an NPN transistor Q4L are connected to the collector of the NPN transistor Q4L.
The base of the transistor Q6 is connected to the ground terminal c from the emitter of the NPN transistor Q6 through the resistor R6, and from the base of the NPN transistor Q6 to the ground terminal c through the base of the transistor Q7 and the resistor j. The collector of transistor Q3 is connected to the emitter of PNP transistor Q7. The temperature detection circuit for such a P-N junction includes an NPN) transistor Q6 and a PNP') transistor.
The collector of the transistor Q is connected to the ground terminal C via the resistor R7, the collector of the transistor Q7 is connected to the base of the transistor Qg, and the emitter of the transistor Qt is connected to the ground terminal C. , the collector becomes the output terminal. It consists of a control circuit consisting of a PNP) transistor Qr and an NPN) transistor Qr.

In general, an overheat protection circuit is a protection circuit that prevents destruction and deterioration of the output circuit due to heat. The temperature of the P-N junction is 73
It is set to operate within 0-200°C.

In particular, in order to keep the width of the variation constant at the top and bottom, it was necessary to set the center of the variation in the above-mentioned operation start temperature to 773°C.

Problems to be Solved by the Invention The operation of the above-mentioned conventional overheat protection circuit will be explained based on FIG. The temperature rise of the P-N junction inside the integrated circuit is PNP) VBK is the P-N junction of transistor Q
The output circuit is The NPN transistor Qr draws the drive current, stopping the output circuit and stopping the integrated circuit to prevent the PN junction of the integrated circuit from being destroyed. Therefore, the following (c.

(,2) K te't VB2 tVBKQ, 7 f
ON), the overheat protection circuit operates when they match.

TVBFiQ7 (ON) -7n (10”/Is)
--(u) Engineering CQ7=vBEQ8(ON)/R7・
・・・・・・・・・・・・・・・・・・(3) VBQ6
: NPN ) Base potential of transistor Q group (overheat protection circuit reference voltage) VBzQ6: NPN ) Base-emitter potential difference of transistor Q6: Boltzmann constant, q: electric charge, T: absolute temperature, s:
Saturation current Therefore, the operating temperature of the conventional overheat protection circuit is determined by the resistance constant and the base potential VBQ4 of the NPN transistor Q6, which is the reference voltage of the overheat protection circuit, and the reference voltage V
BQ b is determined by the following formula (ri).

(, α= AEQ2/AEQ4) ΔVBE = VBEQ4−VBEQ2 ・・・ ・
・・・・・・・・・ (5) Here, PNP) transistor Q5 supplies the current that enables transistor Q7 to operate. There is. Further, this PNP transistor Q3 constitutes a constant current circuit with the PNP transistors Q/ and QJ. Therefore.

Until the overheat protection circuit operates, the PNP) transistor Q
Since the transistor Q3 is not operating, the collector current of the PNP transistor Q3 becomes excessive, and the collector current of the PNP transistor Qt becomes excessive.
is saturated, and the constant current circuit Q3 does not operate normally.

In other words, due to the saturation of the transistor Q5, the base current of the transistor Qr increases and the PNP of the constant current circuit increases.
As the collector current of transistor Q3 decreases, VH2 (potential difference across resistor Re) also decreases, and the above (
France) As shown in Figure 2, the reference voltage VBQ b increases,
VB2 shown in equation (C) increases and the overheat protection circuit operating temperature falls below the set temperature.In other words, since the constant current circuit is not operating normally, the reference bias becomes unstable and the overheat protection circuit operates at There is a drawback that the settings are very difficult to set.Also, the variation in the operating temperature of the overheat protection circuit is due to the variation in resistance, the variation in VBK of the transistor, and the PN
P ) β in the saturated state of transistor Q5 (= IC/I
Since it is determined by the variation of B), there is a drawback that the range of variation is wide.

The present invention has been made in view of the above-mentioned conventional situation,
SUMMARY OF THE INVENTION An object of the present invention is to provide a novel overheating protection circuit which makes it possible to eliminate the above-mentioned drawbacks inherent in the prior art.

Means for Solving the Problems In order to achieve the above object, the overheat protection circuit according to the present invention includes a temperature detection circuit for detecting the temperature of the P-N junction, and a control driven by the output of the temperature detection circuit. A reference voltage circuit including a constant current circuit for setting a reference bias of the temperature detection circuit, and a PNP transistor Qio for preventing saturation of the constant current circuit.

EXAMPLE Next, a preferred embodiment of the present invention will be specifically explained with reference to the drawings.

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

Referring to Figure 1, 1 reference symbol Q/, Qko, Q3゜Q4
', Q'+ Q+, Q? and Q tO is a transistor, Ri.

RJ, RJ, R Hiro, RA, RA, R7 resistor, Q
9 is a constant voltage diode, a is a power supply terminal, b is an output terminal,
C indicates a ground terminal. Transistor Q/.

A reference voltage circuit is composed of Qco@Q3*Qe and resistors R, y, and Re, and the temperature detection circuit that detects temperature from resistor RsVc is composed of transistors Qs, QA, and Q.
10 and resistors R1r, Rh, R? Q7.K, which is a control circuit, is configured by this temperature detection circuit. Q
drive the vehicle.

Note that elements having the same symbols and numbers as those in FIG. 1 above indicate the same elements as in FIG. Further, the basic operation of the overheat protection circuit is the same as that of the conventional circuit shown in FIG.

Here, in the case of the overheat protection circuit of the present invention shown in FIG.
The emitter current of transistor Q/<7 is determined by the reference voltage vBEQ6 and resistor R6 from the collector current of transistor Qr. (NPN)
When transistor Q7 (PNP) operates, the emitter current of transistor Q7 is greater than the current flowing through transistor Qlo. In order to be supplied, PNP which is a constant current circuit
) Transistor Q3 does not saturate.

Therefore, the constant current circuit always operates normally.

As described in detail, according to the present invention, by adding a PNP transistor to a conventional circuit, the surplus current of the constant current circuit is reduced until the P-N junction temperature reaches the operating set temperature of the overheat protection circuit. The above PNP) transistor Q10 creates a bypass with a bypass, which allows the constant current circuit to always operate normally, making it easy to set the operating temperature of the overheating protection circuit. Since the determination is made only by the variation and the variation in VBx of the transistor, the variation factor can be reduced compared to the conventional example, and the effect of narrowing the range of variation in the set temperature can be obtained.

[Brief explanation of the drawing]

FIG. 7 is a circuit configuration diagram showing an embodiment of the overheat protection circuit according to the present invention, and FIG. 1 is a conventional overheat protection circuit diagram.

Claims (1)

[Claims] a reference voltage circuit that includes a temperature detection circuit that detects the temperature of the P-N junction, a control circuit that is driven by the output of the temperature detection circuit, and a constant current circuit that sets a reference bias for the temperature detection circuit; The overheat protection circuit according to the invention, further comprising means for bypassing the current of the constant current circuit from the temperature detection circuit to a bypass circuit before the temperature detection circuit starts operating.