JPS6138486B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a temperature control device that is used by applying alternating current to sensors of electric carpets, electric blankets, etc., and provides a temperature control device that is highly accurate, highly stable, long-life, and safe. The purpose is to provide the following.

Fig. 1 shows a structural diagram of a sensor used in an electric carpet.This sensor 1' has an electrode 2 wound around a core wire 1, and a temperature-sensitive material 3 made of a plastic thermistor placed on top of this electrode 2. coated with
An electrode 4 is wound around the temperature-sensitive material 3, and the electrode 4 is further covered with an insulating jacket 5.
Electric carpets usually use a sensor 1' with a length of several tens of meters, but the plastic thermistor used as the temperature-sensitive material 3 becomes polarized when DC voltage is applied, degrading its characteristics. Care must be taken to ensure that voltage is applied.

FIG. 2 shows a control circuit diagram of a conventional electric carpet temperature control device using the _sensor 1'. , a series circuit of the temperature sensitive material 3 is connected. The potential corresponding to the resistance value of the temperature-sensitive material 3 is generated by a diode 8 branch-connected from the electrode 2;
sensed by transistor 9 and capacitor 1
The temperature signal potential V _T is obtained by integrating to 0. On the other hand, a diode 11, a resistor 12, a resistor 13, and a capacitor 14 provide a set potential V _S . The temperature signal potential V _T is applied to the comparator 1 via a resistor 15.
6, the voltage is compared with the set potential _VS , and the relay 17 is driven to turn on and off the contact 18 to control the heater 19, which is a load, thereby controlling the temperature. Also, a diode 20 and a capacitor 21 provide a DC power source for the relay. 22 is a diode for absorbing back electromotive force of the relay 17, and 23 is a hysteresis resistor. Furthermore, in FIG. 2, the black circles represent connectors that connect the control circuit to the sensors and heaters on the main body side of the electric carpet.

In the above conventional configuration, a of the AC power supply V _AC
When the a side is positive, a series circuit of a diode 8, a transistor 9, and a capacitor 10 is connected in parallel with the temperature sensitive material 3, but when the a side is negative, the diode 8 or transistor 9 becomes reverse biased. As a result, an asymmetrical AC voltage is applied to the temperature-sensitive material 3, which promotes polarization of the sensor 3 and shortens its lifespan, and shifts the control temperature toward a higher temperature side, making it safer. There was also a problem above. Also, if the connector 24 causes poor contact,
The temperature signal potential V _T rises rapidly to the AC power supply voltage,
It also had the disadvantage of destroying the circuit.

The present invention detects the current flowing through a resistor connected from an electrode close to the core wire of the temperature-sensitive material as a collector current with a common-base transistor, and further connects a diode in parallel with the transistor. This eliminates the above-mentioned conventional drawbacks.

FIG. 3 is a control circuit diagram showing one embodiment of the temperature control device of the present invention, and the same numbers as those in FIG. 2 have the same functions. A DC power supply V _CC for the control circuit is obtained by smoothing the AC power supply V _AC with a diode 25 and a capacitor 26 . The side opposite to the a side of the AC power supply Vac is the DC power supply.
It is a common grounding point with Vcc. The resistor 27 and Zener diode 28 create a fixed reference potential V _Z for obtaining the temperature signal voltage V _T and the set potential V _S . The set potential V _S is determined by connecting a resistor 29 to the DC power supply V _CC , detecting and inverting the current flowing through this resistor 29 with a current mirror circuit 30 , and inverting the current flowing through the resistor 31
It can be obtained by generating a voltage at

When the a side of the AC power source V _AC is negative, the current I _T flowing through the resistor 32 connected to the electrode 2 near the core wire 1 of the sensor 1' changes depending on the resistance value of the temperature sensitive material 3. Since the temperature changes in accordance with the temperature detected by the sensor 1', highly accurate temperature control is possible. Further, the current I _T is the emitter current of the base-grounded transistor 33, and it directly becomes the collector current Ic of the transistor 33 (assuming the amplification factor of the transistor is α, Ic = (1-1/α) I _T , the capacitor 34 and a resistor 35, which integrates the signal and converts it into a temperature signal potential V _T.Moreover , if the amplification factor of the transistor is greater than a certain value, the variation or change in the amplification factor will be reduced to Ic. Therefore, the comparator 16 can perform accurate temperature comparisons.

Also, the AC power supply V _AC fluctuates, for example, the AC power supply V
When _AC rises, the current I _T also increases, so the temperature signal potential V _T falls. On the other hand, the DC power supply V _CC also rises due to the rise of the AC power supply V _AC , and the current of the current mirror circuit 30 Since the temperature signal potential V T also increases, the set potential V _S also decreases, and as a result, the decrease in the temperature signal potential V _T is completely corrected. Therefore, even if there is a fluctuation in the AC power supply V _AC , the control temperature does not change at all.

And again, when the a side of the AC power supply V _AC is positive,
The current I _T is reversely directed to the diode 36.
As a result, a completely symmetrical AC voltage is applied to the temperature-sensitive material 3, and as a result, deterioration of the temperature-sensitive material 3 due to polarization can be completely prevented. Further, even if a contact failure occurs in the connector 24, there is no possibility that an excessive voltage will be applied to the control circuit side, and therefore the control circuit will not be destroyed. Further, since the electrode 2 is close to the core wire 1 side, the bending angle is tighter than that of the electrode 4, so there is a high possibility that a disconnection failure will occur, and if the electrode 2 causes a disconnection failure, the current I
As _T becomes extremely small, the temperature signal potential V _T rises and operates to turn off the relay 17.
It's safe.

As is clear from the above description, the temperature control device of the present invention consists of a series circuit in which an AC power supply, a resistor, and a sensor are connected in series so that the electrode farthest from the sensor's core wire side is placed on the ground point side, and a base emitter circuit. A common-base transistor is formed by connecting a series circuit with another resistor in parallel to the sensor, and a diode is connected in parallel and in the opposite direction to the base and emitter of the transistor. Since it has a temperature control circuit that controls the load by comparing the temperature signal potential obtained by voltage conversion with a set potential, it has various excellent features as described below.

(1) Changes in the current flowing through the resistor connected in parallel with the sensor are extracted directly as the collector current of the common-base transistor, converted to voltage, and used as a temperature signal, so it is not affected by variations or changes in the amplification factor of the transistor. Highly accurate temperature control is possible.

(2) Since a completely symmetrical AC voltage is applied to the sensor, it will not deteriorate even if a sensor that is easily polarized such as a plastic thermistor is used, resulting in highly stable, long-life, and safe temperature control. A device is obtained.

(3) Even if a contact failure occurs in the connector that connects the sensor and the control circuit, there is no risk of excessive AC voltage being applied to the control circuit and destroying the circuit.

(4) Even if the electrode on the core wire side of the sensor breaks, it is safe because it will collapse to the side where the control temperature is lower.

[Brief explanation of the drawing]

FIG. 1 is a structural diagram of a sensor, FIG. 2 is a circuit diagram of a conventional temperature control device, and FIG. 3 is a circuit diagram of a temperature control device showing an embodiment of the present invention. 1... Core wire, 1'... Sensor, 2... Electrode, 3
... Temperature-sensitive material, 4 ... Electrode, 6, 7 ... Resistance, 16
... Comparator, 17 ... Relay, 18 ... Relay contact, 19 ... Load (heater), 25 ... Diode, 26 ... Capacitor, 29 ... Resistor, 30 ...
...Current mirror circuit, 31, 32...Other resistors (constitutes a temperature control circuit with the above-mentioned 16, 17, 18, 29, 30, etc.), 33...Transistor, 36
...Diode, V _AC ...AC power supply, I _T ...Current flowing through resistor 32, I _C ...Transistor 3
Collector current of 3, V _T ...Temperature signal potential, V _S ...
...Setting potential, V _CC ...DC power supply.

Claims (1)

[Claims] 1. An AC power source, a DC power source obtained by rectifying the AC power source, an electrode wound around a core wire, a temperature-sensitive material coated thereon, and an electrode further wound around the core wire. a series circuit in which the AC power source, the resistor, and the sensor are connected in series so that the electrode farthest from the core side of the sensor is on the ground point side of the AC power source and the DC power source, and a base connected to the ground point. and a series circuit of its base and emitter and another resistor is connected in parallel to the sensor, a diode connected in parallel and in the opposite direction to the base and emitter of the transistor, and the DC A temperature control device comprising: a temperature control circuit having a control element that compares a temperature signal potential obtained by converting the collector current of the transistor into a voltage and controls a load by comparing a temperature signal potential energized by a power source with a set potential. 2. Connect a resistor to the DC power source obtained by smoothing the AC power source, detect and invert the current flowing through this resistor with a current mirror circuit, and send the output current of the current mirror circuit to another resistor to invert the current flowing through the resistor. The temperature control device according to claim 1, wherein the temperature control device is configured to use the generated voltage as a set potential.