JP2732079B2 - Drive circuit having thermal cutoff circuit - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a drive circuit having a thermal cutoff circuit (hereinafter referred to as a thermal shutdown circuit). More specifically, the present invention relates to a drive circuit having an internal temperature of an IC by detecting an abnormal temperature rise of an IC chip. The present invention relates to an improvement of a thermal shutdown circuit for stopping an operation of a drive circuit.

[Prior art] In a conventional IC including a drive circuit and the like, the IC is destroyed due to an abnormal temperature rise of an IC chip, heat generation and ignition of a substrate and the like on which the IC is mounted, and the peripheral circuits are destroyed and a mechanism to be controlled. In order to prevent damage to the IC, a thermal shutdown circuit is built into the IC as one of the protection circuits.

As the thermal shutdown circuit, a drive circuit integrated into an IC, a transistor integrated with the drive circuit, and the like are used as a temperature detecting element, and the voltage between the base and the emitter depends on the temperature. Detecting and generating a cutoff signal.

FIG. 3 shows an example of such a conventional thermal shutdown circuit, in which the transistor Tr is an NPN transistor for temperature detection and the bias resistors R ₁ and R
_{According to 2} , the voltage between the base and the emitter of the transistor Tr is set to, for example, about 0.4 V.

Usually, the temperature range in which the circuit operates, for example, 0 ° C to 80 ° C
In this range, the voltage between the base and the emitter for operating the NPN transistor Tr is about 0.7 V. Therefore, when the voltage between the base and the emitter is set to the bias state of about 0.4 V as described above. In, there is a transistor
Tr does not enter the “ON” state. However, the transistor Tr
When the temperature of the base reaches about 150 ° C,
The voltage between the emitters drops to around 0.4V.

Therefore, when the temperature of the NPN transistor Tr reaches a temperature set as the detection temperature, for example, 180 ° C., the transistor Tr is turned “ON”, the PNP transistor Tr ₁ of the emitter follower is turned “ON”, and the load resistance R _The temperature detection signal is obtained in FIG. This is output as a cutoff signal (output from OUT ₁ and OUT ₂ ) to a drive circuit that requires a function stop via transistors Tr ₂ , Tr _3, etc., and is applied to each drive circuit to stop the operation of that circuit. .

[Problem to be Solved] However, when the temperature of the drive circuit to be subjected to the thermal shutdown control becomes high, the transistor of the circuit generates a leak current between the collector and the emitter.
Before the thermal shutdown circuit operates, there is a high risk that the drive circuit malfunctions in a range of a temperature equal to or lower than a set temperature and causes an accident, and the temperature of such malfunction of each drive circuit varies.

In addition, since such a thermal shutdown circuit must operate reliably in response to the surrounding temperature environment, a circuit arrangement in which a leak current between the collector and the emitter is unlikely to occur is particularly required. It is indispensable from a circuit design point of view that a thermal shutdown circuit is formed at a position where the thermal shutdown circuit operates reliably at a predetermined high temperature.

Further, in such a thermal shutdown circuit that performs temperature detection by setting the bias between the base and the emitter of the transistor, even if the thermal shutdown circuit is operated before the circuit malfunctions including the variation in the characteristics of the drive circuit, Since the bias setting itself varies, fine setting cannot be performed, and it is difficult to absorb a malfunction by selecting the bias point.

The present invention solves such a problem of the prior art, in which a temperature detection signal can be generated before a drive circuit to be subjected to thermal shutdown control malfunctions, and the layout of the circuit can be reduced. It is an object to provide a drive circuit having an easy thermal cutoff circuit.

[Means for Solving the Problems] In order to achieve such an object, a drive circuit having a heat cutoff circuit according to the present invention has a structure in which a drive circuit driven by a transistor and the heat cutoff circuit are integrated in one chip. Then, the thermal cutoff circuit applies a voltage between the collector and the emitter of the plurality of transistors whose base side is open or connected to a very high impedance, obtains a leak current between the collector and the emitter of the plurality of transistors, and obtains a leakage current between these collectors. A sum signal generates a cutoff signal in a predetermined temperature state, in which a plurality of transistors are dispersedly arranged on a chip, the cutoff signal is supplied to a drive circuit, and the operation of the drive circuit is stopped.

[Operation] As described above, by applying a voltage between the collector and the emitter of the plurality of transistors and detecting the leakage current, a shutdown signal for thermal shutdown at a predetermined temperature is obtained by the sum of the respective leakage currents. Therefore, the malfunction condition that occurs at high temperature due to the leak current between the collector and emitter of the output stage transistor of the drive circuit subject to the thermal shutdown control and the condition for detecting the temperature of the thermal shutdown detection circuit are the same due to the same leak current. Will be. Therefore,
It is possible to generate a thermal shutdown cutoff signal in a range of a leak current that does not cause a malfunction in the drive circuit.

In addition, the leak current for temperature detection is obtained from a plurality of transistors for temperature detection, and a cutoff signal is generated by the sum of the transistors, so that variations in the leak current are absorbed and the operating point for temperature detection is suppressed. Further, since the plurality of transistors for temperature detection are dispersedly arranged on the chip, high-precision temperature detection of the entire IC becomes possible.

As a result, thermal shutdown can be performed before the drive circuit starts malfunctioning due to leakage current, and the temperature detection of thermal shutdown depends on the leakage current between the collector and emitter. Also, only the heat transfer needs to be considered, and the layout can be relatively freely performed.

Since the value of the leak current between the collector and the emitter that is the target of temperature detection is determined by the heat receiving environment of the transistor that performs temperature detection and the temperature environment in which the drive circuit that is the target of temperature control is located, If the heat receiving condition of the transistor described above is made large, the entire detected leak current value can be made large.

Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram of an embodiment in which a drive circuit having a thermal cutoff circuit according to the present invention is applied.
The figure is a block diagram of another embodiment.

In FIG. 1, reference numeral 1 denotes a thermal shutdown circuit which sends a shut-off signal to a drive circuit 2 including a driver stage for driving a motor or an actuator when the temperature of the drive circuit 2 reaches a predetermined or higher temperature. The operation of the drive circuit 2 is stopped.

Here, the drive circuit 2 is a circuit for driving the DC motor M, and includes a plurality of parallel-connected NPN transistors Q ₁₂ , which are connected in series with the coil of the DC motor M.
Q ₁₂ ,... As its driver. The current value of the DC motor M is determined according to the driving operation of the driver, and the rotation speed or the torque thereof is controlled.

A plurality of transistors Q ₁₂ , Q ₁₂ ,.
The bases are commonly connected to the input terminal 2a of the drive circuit 2 and are controlled by receiving the output of the motor drive control circuit 3.

The thermal shutdown circuit 1 has PNP transistors Q ₁ , Q ₂ , Q ₃ ,... For temperature detection connected in parallel, and each base of each PNP transistor for temperature detection is connected to another circuit. It is open without being connected. Then, each emitter is commonly connected to the power supply voltage + V _DD, each collector is connected to the collector of the NPN transistor Q ₁₀ in common.

NPN transistor Q ₁₀ is a NPN transistor Q ₁₁ and the current mirror connected transistors, PNP transistors _{Q 1, Q 2, Q 3} , NPN transistor Q ₁₁ detects a leakage current between the collector-emitter of ... To generate a cutoff signal on its collector side, which is taken out from the output terminal 1a. When the output signal reaches a predetermined temperature state, the output signal is output to the input terminal 2a of the drive circuit 2 to be subjected to thermal shutdown, and the operation of the drive circuit 2 is stopped.

Here, the PNP transistors Q ₁ , Q ₂ , Q ₃ ,... Are normally integrated around the drive circuit 2 to be subjected to thermal shutdown, and the NPN transistors Q ₁₀ , Q ₁₁
Are also formed in the same chip as the drive circuit 2. Therefore, the drive circuit 2 or an IC including this circuit
When the temperature of the entire chip becomes high, the PNP transistor Q
Leakage currents I ₁ , I ₂ , I ₃ ,... Occur between the collectors and emitters of ₁ , Q ₂ , Q ₃ ,. , The sum of the leak currents of the PNP transistors Q ₁ , Q ₂ , Q ₃ ,.
_{I 1 + I 2 + I 3} + ··· is further amplified by the current mirror circuit, by "ON" the NPN transistors Q _11, NPN transistors Q _12, Q _12, to "OFF" state...

In this case, for example, when a PNP transistor is used, a plurality of transistors for generating a leak current for temperature detection should be arranged even if the leakage current is about 180 degrees and about several tens of microamps. Accordingly, the current can be reduced to about 100 microamps, and further, by amplifying and detecting the current by a current mirror circuit, a cutoff signal can be generated.

Therefore, the NPN transistor Q for driving the drive circuit 2
Assuming that the current value of the malfunction due to the leak current between the collector and emitter of No. ₁₂ is Is, the PNP transistors Q ₁ , Q ₂ , Q ₃ ,... since a base open to the transistor Q ₁₂ for driving, the relationship I> is, it is possible to generate a blocking signal in the following current value is, previously its operation the drive circuit 2 may malfunction Can be stopped. Due to the structure of the transistor, NP
Since the temperature at which leakage occurs is lower in a PNP transistor than in an N transistor, the temperature can be more easily detected by using a PNP transistor as a transistor to be detected.

In the above case, PNP that detects temperature by leakage current
Since a plurality of transistors Q ₁ , Q ₂ , Q ₃ ,... Are connected in parallel, variations in leakage current of these transistors are absorbed, and variations in operating points for temperature detection are suppressed. High temperature detection is possible.

Here, when detecting the temperature of the entire IC chip and generating a cutoff signal, the respective PNP transistors Q ₁ , Q ₂ , Q
₃ , ... are distributed in the central part and peripheral part of the IC chip. Thus, the entire IC chip may be a circuit with a temperature sensor, it is also possible to use an external circuit to the output of the NPN transistor Q ₁₁ as a temperature detection signal.

Figure 2 is an embodiment applying the blocking signal to the operation control terminal 3a of the motor drive control circuit 3, which is easy to stop the operation of the drive circuit 2 even with a small driving force of the NPN transistor Q ₁₁ be able to.

As described above, in the embodiment, a plurality of transistors Q ₁ , Q ₂ , Q ₃ ,... Are connected in parallel, and the temperature is detected by the sum of the leakage current values. The temperature can be detected without adjusting the amplification factor as in the case of the temperature detection by the number of transistors.

In the embodiments, a drive circuit for driving a motor is described. However, the present invention is not limited to a drive circuit for driving a motor, and requires a drive current including a drive circuit for various actuators. Can be applied to many drive circuits.

Further, the form of the transistor for detecting the leak current between the collector and the emitter for detecting the temperature may be a PNP transistor or an NPN transistor. Further, although the base of each transistor is open, it may not be completely open and may be connected with a very high impedance.

[Effects of the Invention] As can be understood from the above description, according to the present invention, by applying a voltage between the collector and the emitter of a plurality of transistors and detecting the leak current, a predetermined value is obtained by summing the respective leak currents. Since the shutdown signal for the thermal shutdown at the temperature of is obtained.
The condition of the malfunction that occurs at high temperature due to the leak current between the collector and the emitter of the output stage transistor of the drive circuit subject to thermal shutdown control and the condition of detecting the temperature of the thermal shutdown detection circuit are due to the same leak current. Become. Therefore, it is possible to generate a thermal shutdown cutoff signal in a range of a leak current that does not cause a malfunction in the drive circuit.

In addition, the leak current for temperature detection is obtained from a plurality of transistors for temperature detection, and a cutoff signal is generated by the sum of the transistors, so that variations in the leak current are absorbed and the operating point for temperature detection is suppressed. Further, since the plurality of transistors for temperature detection are dispersedly arranged on the chip, high-precision temperature detection of the entire IC becomes possible.

As a result, the thermal shutdown can be performed before the drive circuit starts malfunction due to the leak current, and the temperature of the thermal shutdown is detected by the leak current between the collector and the emitter. Also, only the heat transfer needs to be considered, and the layout can be relatively freely performed.

[Brief description of the drawings]

FIG. 1 is a block diagram of an embodiment in which a drive circuit having a thermal cutoff circuit of the present invention is applied, FIG. 2 is a block diagram of another embodiment thereof, and FIG. 3 is a conventional thermal circuit. It is a block diagram of a shutdown circuit. 1: thermal shutdown circuit, 2: drive circuit,
3 ... motor drive control _{circuit, Q 1, Q 2, Q} 3 ... PN for detecting temperature
P transistor, Q ₁₀ , Q ₁₁ , Q ₁₂ ... NPN transistor.

 ──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-55-14771 (JP, A) JP-A-61-127156 (JP, A) JP-A-1-293714 (JP, A) JP-A-62 2567 (JP, A) JP-A-60-14873 (JP, A) JP-A-60-86942 (JP, A) JP-A-62-168440 (JP, U)

Claims (2)

(57) [Claims] In a drive circuit having a heat cutoff circuit, a drive circuit driven by a transistor and the heat cutoff circuit are integrated in one chip, and the heat cutoff circuit comprises:
A voltage is applied between the collector and the emitter of a plurality of transistors whose base side is open or connected to a very high impedance, leak currents between the collector and the emitter of the plurality of transistors are obtained, and a predetermined value is obtained by summing the leak currents. Generating a cutoff signal in a temperature state, wherein the plurality of transistors are dispersedly arranged on the chip, the cutoff signal is supplied to the drive circuit, and the operation of the drive circuit is stopped. A drive circuit having a thermal cutoff circuit. 2. A drive circuit having a heat cutoff circuit, wherein a drive circuit driven by a transistor, a drive signal generation circuit for generating a signal for driving the drive circuit, and the heat cutoff circuit are integrated in one chip. The thermal cutoff circuit applies a voltage between the collector and the emitter of a plurality of transistors whose base side is open or connected to a very high impedance, obtains a leak current between the collector and the emitter of the plurality of transistors, and obtains the leak current. Generating a cutoff signal in a predetermined temperature state by a sum of the plurality of transistors. A drive circuit having a thermal cutoff circuit, wherein the drive circuit stops.