JPH061421B2 - Heat shutoff circuit - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat cutoff circuit, and more specifically, a chip incorporated in an integrated circuit chip that generates heat due to power loss in a power stage has a predetermined tolerance. The present invention relates to an improvement of a heat cutoff circuit that cuts off the power stage to prevent chip breakage when it is detected that the temperature exceeds the temperature range.

[Conventional technology]

FIG. 2 shows the configuration of this type of heat cutoff circuit according to a conventional example.

That is, in the circuit shown in FIG. 2, Q ₁ is a first PNP transistor having its collector and base connected and its emitter connected to the power supply, and Q ₂ has its base connected to the base of the first PNP transistor Q ₁ Second PNP with power source connected to
Transistor, Q ₃ is the collector of the first PNP transistor Q
_{A first} NPN transistor connected to the collector of 1, Q ₄ is a second NPN transistor whose base and collector are connected to the collector of the second PNP transistor Q _{2 and} the base of the first NPN transistor Q ₃ , respectively. Q ₅ is the third NPN whose emitter is grounded and whose collector is the output terminal T _OUT
The base of the transistor, Q _6, is the second PNP transistor Q ₂
Of the third NPN transistor Q ₅ with its collector connected to the base of the
, And R ₁ is a first resistor connected between the emitter of the first NPN transistor Q ₃ and ground,
R ₂ is a second resistor connected between the base and the emitter of the third NPN transistor Q ₅ .

In the circuit configuration according to this conventional example, if the transistors Q ₁ and Q ₂ have the same transistor size and the emitter size of the transistor Q ₃ is N times the emitter size of the transistor Q ₄ , _{Since 1} and Q ₂ form a current mirror circuit with a current ratio of 1: 1,
The collector currents of the transistors Q ₃ and Q ₄ are the same, and the following equation holds.

Here, I _E3 ； Emitter current of Q ₃ ； Boltzmann constant T ； Absolute temperature ； Electronic charge Moreover, since transistor Q ₆ shares the base and emitter with transistors Q ₁ and Q ₂ , collector current of transistor Q ₆ It is equal to the collector current of the transistor Q _1, Q _2, therefore, the resistance R ₂ Nikakaru voltage V ₂ is as follows.

At this point, the base-emitter voltage V _BE5 when the transistor Q ₅ starts to turn on has a negative temperature coefficient, while
As shown in the equation (2), the voltage across the second resistor R ₂ has a positive temperature coefficient.

On the other hand, in the constant current circuit according to the conventional configuration, the output transistor Q ₅ can be turned on at a predetermined temperature or higher by appropriately selecting the _second resistor R ₂ . is there.

[Problems to be solved by the invention]

However, in the case of the heat cutoff circuit in the conventional example,
It has the disadvantage that the number of elements that make up the circuit is relatively large,
Further, since the third NPN transistor obtains a current proportional to the current obtained by the first and second PNP and NPN transistors and the first resistance, the third NPN transistor is related to the circuit itself. However, it is not preferable because it is easily affected by variations in device characteristics and voltage dependence between collector and emitter. .

The present invention has been made in order to solve such a problem in the conventional example circuit, and the purpose thereof is to provide a simple circuit configuration in which the number of required elements is reduced and to provide a highly accurate thermal circuit. It is an object of the present invention to provide a thermal cutoff circuit of this kind that can obtain a cutoff performance.

[Means for solving problems]

To achieve the above object, the present invention provides a first resistor between the emitters of the first and second NPN transistors in the circuit configuration using the first and second PNP and NPN transistors described above. A second resistor is connected between the emitter of the second NPN transistor and ground, the base of the third NPN transistor is connected to the emitter of the second NPN transistor, and the emitter is connected to ground. The collector is used as an output terminal.

[Action]

Therefore, in the case of the present invention, the first and second PNPs, NPs
Since the current obtained by the N-transistor and the first resistor is given to the second resistor as it is, it becomes possible to detect the temperature with high accuracy, and it is effective to select the second resistor. In addition to obtaining excellent heat insulation performance, when comparing with the conventional circuit,
The third PNP transistor can be omitted and the circuit configuration can be simplified.

〔Example〕

An embodiment of the heat shutoff circuit according to the present invention will be described in detail below with reference to FIG.

FIG. 1 shows a circuit configuration according to this embodiment. In the circuit of this embodiment of FIG. 1, the same reference numerals as those of the conventional circuit of FIG. 3 indicate the same or corresponding portions.

The circuit of FIG. 1 according to the first embodiment has the same circuit configuration using the first and second PNP transistors Q ₁ and Q ₂ and the NPN transistors Q ₃ and Q ₄ in the conventional example.
Between the NPN transistors Q ₃ and Q ₄
The second resistor R ₂ is connected between the emitter of the second NPN transistor Q ₄ and the ground, and the resistor R ₁ of
The base of NPN transistor Q ₅ is the second NPN transistor
By connecting the emitter of Q _{4 and} the emitter of the same NPN transistor Q ₅ to the ground respectively, the third PNP transistor Q ₆ used in the conventional circuit is omitted, and the third NPN transistor
The collector of the transistor Q ₅ is used as the output terminal T _OUT .

Thisゝis, also in the Figure 1 embodiment circuit, transistor size of the transistors Q _1, Q ₂ are both at the same, the emitter size of the transistor Q ₃ is, if it is N times the emitter of the transistor Q _4, The emitter current I _E3 of the transistor Q ₃ is the same as in the case of the circuit of the embodiment shown in FIG. Next, slave connexion resistor R ₂ Nikakaru voltage V ₂ is Becomes

Also in this embodiment circuit, the base-emitter voltage V _{BE5 at the} time when the transistor Q ₅ starts to turn on has a negative temperature coefficient, while the second resistor R ₂ The negative voltage has a positive temperature coefficient.

Also in the heat cutoff circuit according to this embodiment, the transistor Q ₅ as the output side is set by appropriately selecting the _second resistor R ₂ as in the conventional circuit. It can be turned on at a certain temperature or higher, and output terminal TO
_{Although not} shown in the figure, the output from _OUT cuts off the power stage, which is the cause of heat generation, in the same integrated circuit chip that incorporates the circuit of this embodiment. Can be protected from thermal destruction.

〔The invention's effect〕

As described above in detail, according to the present invention, the first and second
In the circuit using the PNP transistor and the NPN transistor, the first resistor is connected between the emitters of the first and second NPN transistors, and the second resistor is connected between the emitter of the second NPN transistor and the ground. Also the third NP
Since the base of the N-transistor is connected to the emitter of the second NPN transistor and the emitter is connected to the ground, and the collector of the third NPN transistor is used as the output terminal, select the second resistor appropriately. Thus, the current obtained by each of the first and second PNP and NPN transistors and the first resistor can be applied to the second resistor as it is, and therefore the temperature can be detected with high accuracy. It has the advantage of being able to obtain effective heat insulation performance, and since the third PNP transistor can be omitted, it has an excellent feature that the circuit configuration can be provided relatively easily and at low cost. I have.

[Brief description of drawings]

FIG. 1 is a circuit connection diagram showing an embodiment of a heat cutoff circuit according to the present invention, and FIG. 2 is a circuit connection diagram showing a conventional example of the same circuit. Q ₁ …… First PNP transistor, Q ₂ …… Second PNP transistor, Q ₃ …… First NPN transistor, Q ₄ …… Second N
PN transistor, Q ₅ ... 3rd NPN transistor, R ₁ ...
… First resistance, R ₂ …… Second resistance, T _OUT …… Output terminal.

Claims (1)

[Claims] 1. A first PNP transistor having a collector and a base connected to each other and having an emitter connected to a power supply, and a second PNP transistor having a base connected to the base of the first PNP transistor and an emitter connected to a power supply. A first NPN transistor having a PNP transistor and a collector connected to the collector of the first PNP transistor, and a second having a base and a collector connected to the collector of the second PNP transistor and the base of the first NPN transistor, respectively. NPN transistor, a first resistor connected between the emitters of the first and second NPN transistors, a second resistor connected between the emitter of the second NPN transistor and ground, and a base of the second resistor. The third NPN transistor has an emitter connected to the ground of the NPN transistor, and the emitter of the third NPN transistor is connected to the ground. Thermal shutdown circuit, characterized in that the Kuta output terminal.