JPH10201080A - Thermal shutdown circuit - Google Patents

Abstract

(57) [Summary] In a thermal shutdown circuit, a variation in a base-emitter voltage in a manufacturing process of a transistor serving as a temperature sensor is canceled out to reliably operate at a set temperature. SOLUTION: When a base-emitter voltage of a transistor Q1 is used as a temperature sensor, the transistor Q1
The reference voltage V4 obtained by the two resistors R1 and R2 is applied to one base. The constant voltage source 4 outputs a voltage having the temperature dependency of the base-emitter voltage of the transistor Q1 and the temperature dependency of the opposite temperature. The emitter follower circuit 20 allows a current to flow based on the output voltage of the constant voltage source 4, and this current has no temperature dependency, but the transistor Q2
Fluctuates according to the variation of the base-emitter voltage of the transistor. A current having substantially the same value as this current is extracted from the base of the transistor Q1 by the two current mirror circuits 30 and 40.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a thermal shutdown circuit which is one of protection circuits for a driver circuit requiring a large current.

[0002]

2. Description of the Related Art In recent years, in a driver circuit of a motor or a solenoid, even when a chip runs away or an output terminal is short-circuited, a semiconductor product or a semiconductor set emits smoke or fire due to excessive power consumption. Therefore, a thermal shutdown circuit that monitors the semiconductor chip surface temperature and turns off the output stage when the chip surface temperature rises to a certain temperature or higher is required to prevent the temperature from rising.

FIG. 3 shows an example of a conventional thermal shutdown circuit. In the figure, 1 is a power supply, 2 is a ground, and 3 is an output terminal. Reference numeral 50 denotes a bandgap circuit including five transistors Q1 to Q5 and three resistors R1 to R3, and outputs a voltage (bandgap voltage) V0 having no temperature dependency. Q6 is a transistor forming a current mirror circuit in combination with the transistor Q1 having a positive temperature dependency used in the bandgap circuit 50. R4 is a positive temperature dependency transistor provided in the bandgap circuit 50. Is a resistance through which the emitter current of the transistor Q1 flows through the current mirror circuit. The resistance of the resistor R4 has a positive temperature dependency. 51 denotes five transistors Q7 to Q
11, the differential circuit 51 includes a voltage V1 having a positive temperature dependency generated by a current flowing through the resistor R4, and a bandgap voltage V0 of the bandgap circuit 50. Is input to each input terminal. An output stage 52 includes a transistor Q12 and a resistor R5.
2 is controlled by the output voltage of the differential circuit 51.

The bandgap voltage V0 does not depend on the temperature and is about 1.2 V, whereas the voltage V1 generated by the current flowing through the resistor R4 has a positive temperature dependency. By adjusting, the output of the output stage 52 is set to Hi at V1 ≦ V0 below the set temperature.
When the temperature is equal to or higher than the set temperature, the output stage 5
It is possible to configure a thermal shutdown circuit so that the output of No. 2 is set to Lo.

FIG. 4 shows an example of another conventional thermal shutdown circuit. This circuit utilizes the fact that the base-emitter voltage Vbe of a transistor exhibits a negative temperature dependency.

In the thermal shutdown circuit shown in FIG.
The constant voltage V3 is created by dividing the voltage VCC of the power supply 1 by the two resistors R1 and R2. This voltage V
The value of 3 is represented by the following equation (1).

V3 = VCC * R2 / (R1 + R2) (1) Since the voltage V3 is obtained by resistance division, there is no temperature dependency.

[0008] Further, a resistor R3 and a bipolar transistor Q1 constituting an output stage are provided. The transistor Q
1 is controlled by the constant voltage V3.

Next, the operation of the circuit will be described. In general, in a bipolar transistor, when the base-emitter voltage at which the transistor is turned on at room temperature is Vbe0, the temperature coefficient of the base-emitter voltage Vbe is α, the room temperature is T0, and the chip temperature is T, the temperature T When the transistor is turned on, the base-emitter voltage Vbe (O
N) can be approximated by the following equation.

Vbe (ON) = Vbe0 + α (T−T0) (2) Here, specific numerical values are T0 = 27 ° C., α = −2 (mV
/ ° C) and Vbe0 = 700 (mV),
Assuming that the chip temperature T is 127 ° C., the base-emitter voltage Vbe (ON) of the transistor Q1 is as follows: Vbe (ON) = 700−2 * (127−27) = 50
0 (mV).

Therefore, for example, the constant voltage V3 = 500 mV
When the resistance values of the two resistors R1 and R2 are adjusted by the above equation (1) so that
The emitter-to-emitter voltage Vbe (ON)> V3, and the transistor Q1 turns off. When T ≧ 127 ° C., the transistor Q1 turns on. A thermal shutdown circuit is configured using this physical phenomenon.

[0012]

However, in the above-mentioned conventional structure, the base which occurs in the process of manufacturing the transistor is not used.
-The operating temperature of the thermal shutdown circuit varies due to the physical absolute variation of the emitter-to-emitter voltage Vbe.

Generally, the absolute variation of the base-emitter voltage Vbe in the manufacturing process is said to be 20 mV. The base-emitter voltage Vbe (ON) of an operating transistor is approximately expressed by the following equation (3), where the absolute variation is ΔVbe.

Vbe (ON) = Vbe0 + α (T−T0) + ΔVbe (3) In the circuit of FIG. 3, the absolute variation of the base-emitter voltage Vbe of the transistor Q4 becomes the variation of the bandgap voltage V0 as it is. In the circuit of FIG. 4, the absolute variation of the base-emitter voltage Vbe of the transistor Q1 affects the operating temperature of the thermal shutdown circuit.

That is, for example, the absolute variation ΔVbe =
In the case of 20 mV, any of the circuits in FIG. 3 and FIG.
The variation ΔT of the operating temperature from the set temperature is as follows: ΔT = −ΔVbe / α = 20 (mV) / 2 (mV / ° C.)
= 10 ° C.

An object of the present invention is to provide a thermal shutdown circuit capable of reliably operating at a predetermined set temperature.

[0017]

In order to achieve the above object, according to the present invention, there is provided a method of manufacturing a transistor comprising:
A configuration capable of canceling the absolute variation ΔVbe of the voltage between the emitters is adopted.

That is, a thermal shutdown circuit according to a first aspect of the present invention includes a transistor using a base-emitter voltage as a temperature sensor, a reference voltage generating circuit for applying a reference voltage to the base of the transistor, A constant voltage source for outputting a voltage having a temperature characteristic opposite to the temperature dependency of the emitter-to-emitter voltage; and a transistor having a base connected to the constant voltage source, and a current based on an output voltage of the constant voltage source. A current circuit for flowing
And a pull-out circuit for pulling out a current equal to a current value passed by the current circuit from a base of the transistor.

According to a second aspect of the present invention, in the thermal shutdown circuit of the first aspect, the reference voltage generating circuit comprises a circuit in which two resistors R1 and R2 are connected in series. The base of the transistor is connected to a connection point, and the current circuit includes a transistor having a base connected to a constant voltage source, and a resistor R4 connected in series with the transistor. The values of the three resistors are: R1 * R2 / R4 / (R1 + R2) = 1 is set.

Further, according to a third aspect of the present invention, in the thermal shutdown circuit according to the first or second aspect, the current circuit comprises two current mirror circuits.

According to a fourth aspect of the present invention, in the thermal shutdown circuit according to the first or second aspect, the constant voltage source has a resistor between its output and a common impedance, It is characterized by comprising a bandgap reference circuit capable of variably setting the temperature dependence of the output voltage by adjusting the value.

With the above arrangement, in the inventions according to the first to fourth aspects, the current flowing from the current circuit has no temperature dependency and depends on the absolute variation of the base-emitter voltage of the transistor provided in the current circuit. Therefore, the base potential of the transistor serving as the temperature sensor also changes according to the absolute variation of the base-emitter voltage of the transistor provided in the current circuit. On the other hand, the absolute variation of the base-emitter voltage of the transistor serving as the temperature sensor is substantially the same as the absolute variation of the base-emitter voltage of the transistor provided in the current circuit in the same chip. Are offset by the absolute variation of the transistor serving as the temperature sensor. As a result, even if the transistor serving as a temperature sensor has an absolute variation in the base-emitter voltage in the manufacturing process, the operating temperature does not fluctuate according to the absolute variation, and the transistor operates reliably at a predetermined set temperature. Will be.

[0023]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows an equivalent circuit of the thermal shutdown circuit according to the first embodiment of the present invention.

In the figure, 1 is a power supply, 2 is a ground,
3 is an output terminal, and 4 is a constant voltage source. Q1 is base-
An NPN transistor whose emitter-to-emitter voltage serves as a temperature sensor, having a collector connected to the output terminal 3, an emitter connected to the ground 2, a base connected to a node V4, and a reference voltage for applying a reference voltage to the node V4. Each is connected to the generation circuit 10. The reference voltage generating circuit 10 comprises a series circuit of two resistors R1 and R2. One end of the resistor R1 is connected to the power supply 1 and the other end is connected to the base of the NPN transistor Q1. The other resistor R2
Has one end connected to the base of the NPN transistor Q1 and the other end connected to the ground 2.

One end of a resistor R3 is connected to the output terminal 3, and the other end of the resistor R3 is connected to the power supply 1.

The constant voltage source 4 has a positive terminal connected to the power source 1.
The output voltage VREG has a characteristic opposite to the temperature dependence of the base-emitter voltage of the NPN transistor Q1 serving as the temperature sensor.

In FIG. 1, reference numeral 20 denotes an emitter follower circuit (current circuit). This circuit 20 is an NP circuit whose base is connected to the negative terminal of the constant voltage source 4.
An N-transistor Q2 includes a resistor R4 having one end connected to the emitter of the NPN transistor Q2. The other end of the resistor R4 is connected to the ground 2.

Further, 30 is a first current mirror circuit,
Reference numeral 40 denotes a second current mirror circuit, and the first current mirror circuit 30 includes two PNP transistors Q3 and Q4, and one PNP transistor Q3
Has its emitter connected to the power supply 1 and its base and collector connected to the collector of the NPN transistor Q2 of the emitter follower circuit 20, respectively. The other PNP transistor Q
Reference numeral 4 denotes an emitter connected to the power supply 1 and a base connected to the base of the one PNP transistor Q3. The second current mirror circuit 40 includes two NPN transistors Q5 and Q6. One of the NPN transistors Q5 has an emitter connected to the ground 2 and a base and a collector connected to the other of the first current mirror circuit 30. PN
Connected to the collector of P transistor Q4. N of the other
The PN transistor Q6 has an emitter connected to the ground 2, a base connected to the base of one NPN transistor Q5, and a collector connected to the NPN transistor Q1 serving as the temperature sensor.
(Node V4). A pull-out circuit 50 is formed by the two current mirror circuits 30 and 40.

Next, the operation of the thermal shutdown circuit according to the present embodiment will be described. Although the resistance value originally has a temperature dependency, this is initially ignored for the sake of simplicity of logic, and finally, the temperature dependency of the resistance will be discussed.

The constant voltage source 4 and the emitter follower circuit 20
Constant current source I1 by the transistor Q2 and the resistor R4.
Is formed. Since the emitter follower type is used, the current flowing from the constant current source I1 (shown by the same reference numeral I1)
The resistor R4 has the same value as the resistor R4, the voltage of the power supply 1 is VCC, the output voltage of the constant voltage source 4 is VREG, and the transistor Q2 of the emitter follower circuit 20 is turned on.
If the voltage between the emitters is Vbe (ON), then I1 = (VCC-VREG-Vbe (ON)) / R4.

Here, assuming that the output voltage of the constant voltage source 4 at room temperature is VREG0, the output voltage VREG of the constant voltage source is
Since the temperature dependence is set to be opposite to the temperature dependence of the base-emitter voltage of the transistor Q2, it is expressed by the following equation.

VREG = VREG0−α (T−T0) (4) This equation (4) and the equation (3) are substituted into the equation of the current I1 flowing from the constant current source, and I1 = (VCC−VREG0) −Vbe0−ΔVbe) / R4 = (VCC−VG−ΔVbe) / R4 (5) However, VG = VREG0 + Vbe0. From the expression (5), it can be seen that the current I1 has no temperature dependency because the term of the temperature coefficient α is canceled out, and changes only by the absolute variation ΔVbe of the base-emitter voltage.

Next, the two current mirror circuits 30, 4
0 plays a role of extracting a current having a value equal to the current I1 flowing from the constant current source from the node V4 connected to the base of the transistor Q1 serving as a temperature sensor.

Further, a transistor Q1 and three resistors R1
R3 together with the current source I1 constitute a temperature sensor circuit. The resistance values of the resistors R1 and R2 are denoted by R1 and R2, respectively, having the same sign, and a transistor Q1 serving as a temperature sensor is provided.
, That is, the voltage of the node V4 is
The following equation (6) is obtained from the current conservation law.

(VCC−V4) / R1 = V4 / R2 + I1 (6) When the equation (6) is solved for the voltage V4 of the node, V4 = R2 / (R1 + R2) * VCC−I1 * R1 * R
2 / (R1 + R2) The following equation (7) is obtained by substituting the equation (5) for the current I1 in this equation.

V4 = R2 / (R1 + R2) * VCC + R1 * R2 / R4 / (R1 + R2) * (ΔVbe-VCC + VG) (7) Here, R1 * R2 / R4 / (R1 + R2) = 1 (8) When resistance values R1, R2 and R4 are set to
Equation (7) is converted to the following equation (9).

V4 = (VG−R1 / (R1 + R2) * VCC) + ΔVbe (9) As can be seen from the above equation (9), the node potential V4 which is the base potential of the transistor Q1 serving as a temperature sensor has a constant value (VG Based on -R1 / (R1 + R2) * VCC), it changes in conjunction with the absolute variation ΔVbe of the base-emitter voltage of the transistor Q2.

The absolute variations ΔVbe of the base-emitter voltages of the two transistors Q1 and Q2 have substantially the same value in the same chip. Therefore, the thermal shutdown circuit operates when the equations (3) and (9) are equal and Vbe (ON) = V4 (10). When the operating temperature T is obtained from this equation, T = T0− (Vbe0− (VG−R1 / (R1 + R2) * VCC)) / α (11) From the above equation (11), it can be seen that the temperature T at which the thermal shutdown circuit of FIG. 1 operates is not affected by the absolute variation ΔVbe of the base-emitter voltage.

Next, the influence of the temperature dependence of the resistance value will be considered.

Generally, when the temperature T is the normal temperature T0 (T = T
Assuming that the resistance value of (0) is Rn0, the resistance value Rn is known to be Rn = Rn0 * (1 + β * (T−T0) + γ * (T−T0) ² ) (12) Here, β and γ are the temperature coefficients of the resistors, and if the resistors are of the same type in the same chip, they have substantially the same value for all the resistors.

Equations (8) and (11) determine the temperature T at which the thermal shutdown circuit of FIG. 1 operates. In each of these equations, the resistances R1 to R4 are used to determine the above equation (1).
It can be seen that even if 2) is substituted, the temperature coefficients β and γ are canceled out and are not affected by the temperature dependence of the resistance.

FIG. 2 shows an equivalent circuit of the thermal shutdown circuit according to the first embodiment. In the figure, the constant voltage source 4 of FIG. 1 is connected to six transistors Q7 to Q1.
2 and a bandgap reference circuit composed of three resistors R5 to R7. The resistor R6 is arranged between the output and the power supply 1 (common impedance). The voltage corresponding to the output voltage VREG of the constant voltage source 4 is a potential difference between both ends of the resistor R6. In the bandgap reference circuit, if the resistance value of the resistor R6 is adjusted together with the other two resistors R5 and R7, the output voltage VR
Since the temperature dependence of the EG can be set variably, the resistance value is set so as to satisfy the above equation (4). At this time, the value of the output voltage VREG is not affected by the absolute variation ΔVbe of the base-emitter voltage.

In the present embodiment, the base-emitter voltage Vbe of the NPN transistor Q1 is used as a temperature sensor, but the PNP transistor is used as a temperature sensor.
Invert the power supply and ground, and connect the PNP transistor and NP
Of course, a circuit configuration in which the N transistor is inverted may be used.

[0045]

As described above, according to the thermal shutdown circuits of the first to fourth aspects of the present invention, the absolute variation of the base-emitter voltage Vbe in the manufacturing process of the transistor serving as the temperature sensor is canceled. As a result, it is possible to eliminate the fluctuation of the operating temperature due to the absolute variation and to reliably operate at a predetermined set temperature.

[Brief description of the drawings]

FIG. 1 is an equivalent circuit diagram of a thermal shutdown circuit according to a first embodiment of the present invention.

FIG. 2 is a diagram illustrating a specific configuration of a thermal shutdown circuit according to the first embodiment of the present invention.

FIG. 3 is an equivalent circuit diagram of a conventional thermal shutdown circuit.

FIG. 4 is an equivalent circuit diagram of another conventional thermal shutdown circuit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Power supply 2 Ground 3 Output terminal 4 Constant voltage source Q1 Transistor used as a temperature sensor 10 Reference voltage generating circuits R1 to R4 Resistance 20 Emitter follower circuit (current circuit) Q2 Transistor 30 First current mirror circuit 40 Second current mirror circuit 50 drawing circuit

Claims (4)

[Claims] A transistor having a base-emitter voltage as a temperature sensor; a reference voltage generating circuit for applying a reference voltage to the base of the transistor; and a transistor having a characteristic opposite to the temperature dependence of the base-emitter voltage of the transistor. A constant voltage source that outputs a voltage having a temperature characteristic, a current circuit that includes a transistor having a base connected to the constant voltage source, and flows a current based on an output voltage of the constant voltage source; and a current that flows through the current circuit. A circuit for extracting a current equal to a value from the base of the transistor. 2. The reference voltage generating circuit includes two resistors R1,
R2 is connected in series, the base of the transistor is connected to the connection point of the two resistors, and the current circuit is a transistor having a base connected to a constant voltage source, and a resistor connected in series with the transistor. 2. The thermal shutdown circuit according to claim 1, wherein R3 is set to R1 * R2 / R4 / (R1 + R2) = 1. 3. The thermal shutdown circuit according to claim 1, wherein the current circuit comprises two current mirror circuits. 4. The constant voltage source is provided with a resistor between its output and a common impedance, and is constituted by a bandgap reference circuit capable of variably setting a temperature-dependent characteristic of an output voltage by adjusting a value of the resistor. 3. The thermal shutdown circuit according to claim 1, wherein: