JPH07114354B2 - High temperature leak compensation circuit for transistor control circuit - Google Patents

Description

TECHNICAL FIELD The present invention relates to a circuit for compensating a malfunction due to a leak current of a transistor at a high temperature in a transistor control circuit which controls a circuit by the transistor.

(B) Conventional Technology A transistor control circuit for performing circuit control using a plurality of transistors has been conventionally used for circuits in various devices. FIG. 3 is a circuit diagram of a basic configuration portion of such a transistor control circuit. In the figure, Q1 is an NPN type transistor, Q2 is a PNP type transistor, and the collector current of Q2 controls the base current of Q1. A control circuit (not shown) is connected to the base of Q2, and a drive circuit (not shown) is connected to the collector of Q1.

(C) Problems to be solved by the invention Although many transistor control circuits of this type are incorporated in an IC, at high temperature operation (100 to 200 ° C), which is one of the electrical characteristics required for the IC. Designed to maintain the reliability of. In particular, the thermal shutdown circuit, which shuts off the circuit by detecting an abnormal temperature rise in the controlled device or circuit, is originally used in a high temperature atmosphere.Therefore, the circuit design is designed to ensure stable operation at high temperature ing. In the example of the transistor control circuit shown in FIG. 3, especially the PNP transistor Q2 has a relatively large leak current at high temperature, and this leak current may cause malfunction of turning on Q1. A method of inserting a resistor for absorbing leakage current between the base and emitter of Q1 has been adopted as a measure to prevent malfunction due to such leakage current, but it cannot absorb the leakage current sufficiently and the base of Q1 There was a problem such as an offset in the potential.

An object of the present invention is to provide a high temperature leak compensating circuit for a transistor control circuit which prevents malfunction due to a leak current of a transistor during high temperature operation.

(D) Means for Solving the Problems The high temperature leakage compensation circuit of the transistor control circuit according to the present invention comprises a first transistor and a second transistor for controlling a base current of the first transistor by a collector current. A transistor control circuit including: a bias circuit that changes the base voltage of the second transistor according to temperature; and two transistors that form a current mirror circuit, and the second transistor has a temperature-leakage current characteristic. Is connected to the collector of the input side transistor of the current mirror circuit, and the base of the third transistor is opened.

(E) Function In the high temperature leakage compensation circuit of the transistor control circuit of the present invention, a current mirror circuit is composed of two transistors, and the third transistor whose temperature-leakage current characteristic is similar to that of the second transistor is a current mirror circuit. Is connected in series to the collector of the input-side transistor, and the base of the first transistor is connected to the collector of the output-side transistor of the current mirror circuit. A bias circuit changes the base voltage of the second transistor according to temperature. The base of the third transistor is open. Therefore, the leak current of the third transistor flows through the collector of the input side transistor of the current mirror circuit. Therefore, the collector current of the input side transistor, that is, the same current as the leak current of the third transistor flows through the collector of the output side transistor of the current mirror circuit. Therefore, the leak current component of the current flowing through the second transistor flows through the output side transistor of the current mirror circuit, and the other component becomes the base current of the first transistor. As described above, without being affected by the leak current flowing through the first transistor to the second transistor,
It can be operated by a bias circuit.

(F) Embodiment FIG. 1 is a circuit diagram of a high temperature leak compensation circuit of a transistor control circuit according to an embodiment of the present invention. Here, Q1 and Q2 correspond to the first transistor and the second transistor according to the present invention. Q3 is a third transistor having the same temperature-leakage current characteristics as the second transistor Q2. Q
4, Q5 are two transistors forming a current mirror circuit as shown, Q4 is an input side transistor, and Q5 is an output side transistor. Q3 is connected in series between Q4 and the power supply Vcc. Furthermore, the base of Q1 is connected to the collector of Q5. Note that the base of Q3 is in an open state with no other connections. A bias circuit that changes the voltage with temperature is connected to the base of Q2.

If the collector current of Q4 is I1, the collector current of Q2 is I2, the collector current of Q5 is I3, and the base current of Q1 is I0, the following relationship holds. A leak current flows through Q2 during high temperature operation, and its value is equal to the leak current I1 of Q3. Since Q4 and Q5 act as a current mirror circuit, I1 =
I3. Therefore, the leak current contained in I2 is absorbed as the collector current of Q5, and the original control current I0 becomes the base current of Q1. Therefore, Q1 can be operated without being affected by the leak current.

FIG. 2 is a circuit diagram in which the circuit shown in FIG. 1 is applied to a thermal shutdown circuit of a motor. As apparent from comparison with FIG. 1, the voltage dividing circuit formed by the resistor R1 and the temperature sensitive resistor R2 is connected to the base of the transistor Q2. Also, the motor and the transistors Q6 and Q6 that control the on / off of the motor.
A motor control circuit for on / off control of is provided, and the collector of Q1 is connected to the base of Q6. Normal
The on / off control of Q6 is performed by the signal of the motor control circuit, but when the motor M becomes abnormally overheated, the resistance value of R2 drops and Q2 turns on. This turns on Q1
Q6 is forced off. In this case, even if the temperature of the entire circuit rises due to the heat generated by the motor, etc.
The leakage current of Q2 is absorbed by Q5 and does not affect Q1, so there is no malfunction such that Q1 is turned on and Q6 is cut off before the set temperature is reached.

(G) Effect of the Invention As described above, according to the present invention, it is possible to absorb the leak current of the transistor during high-temperature operation.
It is possible to configure a highly reliable transistor control circuit that does not malfunction over a wide temperature range.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a high temperature leak compensation circuit of a transistor control circuit according to an embodiment of the present invention, and FIG. 2 is a circuit diagram in which the circuit is applied to a thermal shutdown circuit of a motor. FIG. 3 is a circuit diagram of a basic constituent portion of a general transistor control circuit. Q1 ... First transistor, Q2 ... Second transistor, Q3 ... Third transistor, Q4, Q5 ... Current mirror circuit.

Claims (1)

[Claims] 1. A transistor control circuit comprising a first transistor and a second transistor for controlling a base current of the first transistor with a collector current, wherein a base voltage of the second transistor is controlled by temperature. A bias circuit to be changed and two transistors forming a current mirror circuit are provided, and a third transistor whose temperature-leakage current characteristic is similar to that of the second transistor is a collector of the input side transistor of the current mirror circuit. High temperature leakage of the transistor control circuit, wherein the base of the first transistor is connected to the collector of the output side transistor of the current mirror circuit, and the base of the third transistor is opened. Compensation circuit.