JPH0548852B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a temperature switch device, and more particularly to a temperature switch device that operates by detecting the temperature of cooling water in an engine of an automobile or the like.

[Prior Art] FIG. 3 is a circuit diagram showing an example of a conventional temperature switch device. First, the configuration of a conventional temperature switch device will be explained with reference to FIG. The positive side of the automobile battery 1 as the first potential is connected to one end of the lamp 3 via the switch 2.
The second potential of the automobile battery 1 is grounded. The lamp 3 lights up when the cooling water reaches a predetermined temperature. The other end of the lamp 3 is connected to a positive temperature coefficient thermistor 9 via a resistor 8. Resistor 8 is for current limiting. The positive temperature coefficient thermistor 9 has a positive temperature coefficient whose resistance value increases as the temperature increases. The positive temperature coefficient thermistor 9 is housed in a case 10, and the case 10 is immersed in cooling water 11.

A capacitor 4 for absorbing surges and the like and a thyristor 5 are connected between the other end of the lamp 3 and the ground. The gate terminal of the thyristor 5 is grounded via a resistor 6 and connected via a Zener diode 7 to a connection point between a resistor 8 and a positive temperature coefficient thermistor 9. The Zener diode 7 levels-shifts the gate voltage required to trigger the thyristor 5.

In the temperature switch device configured as described above, when the cooling water 11 is cold,
Since the resistance value of the positive temperature coefficient thermistor 9 is small, no gate current is supplied to the gate terminal of the thyristor 5 even if the switch 2 is closed. Therefore, the thyristor 5 is turned off. When the automobile engine is started, the temperature of the cooling water 11 rises, and the resistance value of the positive temperature coefficient thermistor 9 changes in the positive direction. Following this, the midpoint voltage V _M between the resistor 8 and the positive temperature coefficient thermistor 9 also increases. When the water temperature reaches a point where this midpoint voltage V _M becomes (the gate voltage of the thyristor) + (the Zener voltage of the Zener diode), a gate current begins to flow to the gate terminal of the thyristor 5.
Thyristor 5 is thereby turned on. When the thyristor 5 is turned on, current flows from the battery 1 to the lamp 3 via the switch 2, and the lamp 3 lights up, indicating that the cooling water has reached a predetermined temperature.

[Problems to be Solved by the Invention] In the conventional temperature switch device configured as described above, the midpoint voltage between the resistor 8 and the positive temperature coefficient thermistor 9 necessary for turning on the thyristor 5 is
V _M is V _M = (resistance value of positive temperature coefficient thermistor 9 x battery voltage) / (resistance value of resistor 8 + resistance value of positive coefficient thermistor 9)
=K1×Battery voltage...(1) Therefore, when the voltage of battery 1 changes, the midpoint voltage V _M changes by K1×(change in battery voltage), and the corresponding thyristor 5 turns on. The temperature will shift. In other words, the temperature of the cooling water 11 when the thyristor 5 is turned on greatly influences the voltage change of the battery 1, resulting in a drawback as a temperature sensor.

Therefore, a primary objective of the present invention is to provide an inexpensive temperature switch device that resists changes in power supply voltage without affecting the detected temperature.

[Means for solving the problem] In the temperature switch device according to the present invention, a connection point between a resistor and a thermistor connected in series between a first potential and a second potential is configured by two PNP transistors. The connection point between two resistors connected in series between the first potential and the second potential is connected to the base of the other pnp transistor. , the collector of one PNP transistor of the differential amplifier is connected to the gate terminal of the thyristor, and the collector is connected to the anode terminal of the thyristor.

[Function] The temperature switch device of the present invention reduces the difference when the resistance value of the thermistor changes as the temperature rises and the voltage at the connection point between the resistor and the thermistor changes more than the voltage at the connection point between the two resistors. A gate current is passed from the collector of one PNP transistor of the dynamic amplifier to the gate terminal of the thyristor to turn on the thyristor and supply current to the load. Thereby, even if the first potential and the second potential vary, the voltage at the connection point between the two resistors also varies, so the detected temperature is not affected.

[Embodiment] FIG. 1 is an electrical circuit diagram of an embodiment of the present invention. In Figure 1, a battery 1, a switch 2, a lamp 3, a capacitor 4, a thyristor 5, and a resistor 6 are shown.
The same one as in FIG. 1 above is used. A first series connection consisting of a resistor 17 and a negative characteristic thermistor 18 is connected between the positive potential as the first potential supplied from the battery 1 via the switch 2 and the lamp 3 and the ground as the second potential. When the circuit is connected, a second series circuit consisting of two resistors 12 and 13 is connected. The negative characteristic thermistor 18 is placed in a case in the same manner as in FIG. 3 described above, and the case is immersed in cooling water.

The base of one PNP transistor 16 constituting the differential amplifier is connected to the connection point between the resistor 17 and the negative characteristic thermistor 18, and the base of the other PNP transistor 16 constituting the differential amplifier is connected to the connection point between the resistors 12 and 13. PNP
The base of transistor 14 is connected. A current limiting resistor 15 is connected between the first potential and the emitters of the PNP transistors 14 and 16.
Further, the collector of the PNP transistor 14 is grounded, and the collector of the PNP transistor 16 is connected to the gate terminal of the thyristor 5.

In the temperature switch device constructed as described above, when switch 2 is closed, current flows from switch 2 through lamp 3 to resistors 12 and 13. Then, the voltage divided by the resistors 12 and 13 is applied to the base of the PNP transistor 14 as a comparison voltage. The PNP transistor 14 is turned on because a forward bias voltage is applied between its base and emitter. On the other hand, in the PNP transistor 16, when the cooling water is cold, the resistance value of the negative characteristic thermistor 18 is large, so the base
A bias voltage is applied between the emitters, turning it off. Since the PNP transistor 16 is in the off state, the thyristor 5 is also in the off state.

When the automobile engine is started, the temperature of the cooling water begins to rise, and the resistance value of the negative characteristic thermistor 18 also decreases. Following this, the midpoint voltage V _M of the resistor 17 and the negative characteristic thermistor 18 also decreases, and the midpoint voltage V _M of the two voltage dividing resistors 1
When the water temperature reaches the same voltage as the comparison voltage V _F obtained by 2 and 13, the ON state is reached.
The PNP transistor 14 turns off, and the PNP transistor 16, which was in the off state, begins to turn on. As a result, a gate current begins to flow to the gate terminal of the thyristor 5, and the thyristor 5 is turned on. When the thyristor 5 is turned on, current flows through the lamp 3, which lights up to notify that the cooling water has reached a predetermined temperature.

Here, when the voltage of battery 1 changes, the midpoint voltage required for thyristor 5 to turn on is
V _M is V _M = (resistance value of negative characteristic thermistor 18 x battery voltage) / (resistance value of resistor 17 + resistance value of negative characteristic thermistor 18)
= K2 × battery voltage...(2), and it changes by K2 (change in battery voltage), but at the same time, the comparison voltage V _F obtained by voltage dividing resistors 12 and 13 also changes by V _F (change in resistor 13). value x battery voltage)/(value of resistor 12 + resistance
13)=K3×Battery voltage...(3) When thyristor 5 turns on,
Since the voltage division ratio (K2 = K3 is selected) is set so that V _F = V _M , the same changes occur. For this reason, there is almost no temperature deviation of the cooling water when the thyristor 5 is turned on.

In other words, the dependence of temperature when the thyristor 5 is turned on with respect to fluctuations in the voltage of the battery 1 is eliminated. Therefore, even if the voltage of the automobile battery 1 fluctuates, it is possible to accurately notify that the temperature of the cooling water has reached a predetermined temperature.

FIG. 2 is an electrical circuit diagram showing another embodiment of the invention. In the embodiment shown in FIG. 2, a positive characteristic thermistor 19 is connected in place of the resistor 17 shown in FIG. 1, and a resistor 20 is connected in place of the negative characteristic thermistor 18. When the positive temperature coefficient thermistor 19 is used in this way, the resistance value is small when the cooling water is cold, so the voltage between the base and emitter of the transistor 16 is low, and the transistor 16 does not conduct. As the temperature of the cooling water rises, the resistance value of the PTC thermistor 19 increases, and the voltage between the base and emitter of the transistor 16 increases, causing the transistor 16 to conduct. is also conductive.

In the above-described embodiments, the present invention has been described for detecting the temperature of automobile cooling water, but it goes without saying that the present invention can be used for other temperature detections.

[Effects of the Invention] As described above, according to the present invention, the connection point between the resistor and the thermistor connected in series between the first potential and the second potential is connected to the difference configured by two PNP transistors. The connection point between two resistors connected in series between the first potential and the second potential is connected to the base of one of the PNP transistors of the dynamic amplifier. Since the collector of the pnp transistor is connected to the gate terminal of the thyristor and the load is connected to the anode terminal of the thyristor, even if the potential between the first potential and the second potential fluctuates, the differential amplifier Since the comparison voltage applied to the input of one of the PNP transistors fluctuates, it does not affect the detected temperature.

[Brief explanation of the drawing]

FIG. 1 is an electrical circuit diagram of an embodiment of the present invention. FIG. 2 is an electrical circuit diagram of another embodiment of the invention. FIG. 3 is a circuit diagram showing a conventional temperature switch device. In the figure, 1 is the battery, 2 is the switch, and 3 is the battery.
is a lamp, 4 is a capacitor, 5 is a thyristor,
6, 12, 13, 15, 17, 20 are resistances, 1
4 and 16 are PNP transistors, 18 is a negative characteristic thermistor, and 19 is a positive characteristic thermistor.

Claims (1)

[Claims] 1. A first series circuit comprising a resistor and a thermistor and connected between a first potential and a second potential, between the first potential and the second potential. The second series circuit has two resistors connected in series, and the two resistors have their respective emitters connected in common.
The base of one pnp transistor is connected to the connection point between the resistor and the thermistor of the first series circuit, and the base of the other pnp transistor is connected to the connection point of the two resistors of the second series circuit. the collector is connected to the second
a differential amplifier whose commonly connected emitter is connected to the first potential through a resistor, the gate terminal of which is connected to the collector of the one PNP transistor of the differential amplifier; A temperature switch device comprising: a thyristor; and a load connected to an anode terminal of the thyristor. 2. The thermistor is a negative characteristic thermistor, and the resistor of the first series circuit is connected between the base of the one PNP transistor and the first potential, and the negative characteristic thermistor is a negative characteristic thermistor. 2. The temperature switch device of claim 1, wherein the temperature switch device is connected between the base of the temperature switch and the second potential. 3. The thermistor is a positive characteristic thermistor, the positive characteristic thermistor is connected between the base of the one PNP transistor and the first potential, and the resistor of the first series circuit is connected to the one PNP transistor. 2. The temperature switch device of claim 1, wherein the temperature switch device is connected between the base of the temperature switch and the second potential.