JPH047557B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to an overtemperature rise prevention circuit in a temperature control circuit of an electric carpet or the like.

(Background Art) Fig. 2 shows a conventional temperature control circuit, in which a heater H of a heating element 11 is connected to a commercial power source via a contact ry of a relay Ry, and the temperature control circuit is controlled according to temperature changes of the heating element 11. This is to drive relay Ry to bring the temperature to the desired temperature. That is, two temperature detection electrodes S ₁ and S ₂ are provided near the heater H of the heating element 11 with a heat sensitive body 11a such as an organic semiconductor sandwiched therebetween, and one temperature detection electrode S ₁ has a sensor voltage divider. By applying a commercial voltage through the circuit 13 and connecting the other temperature detection electrode _S2 to one end of the heater H, an AC voltage signal corresponding to the impedance change of the heat sensitive element 11a, that is, the temperature change, is obtained. By rectifying and smoothing the signal from the sensor voltage detection circuit 14, a DC-like temperature detection signal having a characteristic of decreasing as the temperature rises is obtained.

Then, by comparing this signal with the set voltage given by the variable resistor VR in the comparator CP ₁ , it is determined whether the temperature is above or below a predetermined temperature, and if it is lower than the set temperature, the voltage _is to drive relay Ry and heater H.
On the other hand, if the temperature is higher than the set temperature, the power supply to the heater H is stopped to maintain the heating element 11 at a constant temperature.

On the other hand, comparator CP ₂ inputs the temperature detection signal mentioned above to its inverting input terminal, and its non-inverting input terminal receives a voltage lower than the _set temperature of comparator _{CP 1 (} at higher temperature )
If the heater H becomes continuously energized due to welding of the relay contact ry, etc., and the temperature rises abnormally, the output is reversed and the thyristor
The SCR is turned on to cause the resistor _R11 to generate heat, and the temperature fuse TF, which is thermally coupled to the resistor _R11 , is fused to avoid danger.

By the way, the above operation when the temperature rises is guaranteed in case of welding of relay contacts or conduction failure of relay drive transistor, etc., but operation is guaranteed in case of failure of comparator or failure of temperature setting/over-rise temperature setting resistor, etc. If continuous energization occurs due to a fault such as a short or open circuit, there is a risk that the circuit will become inoperable because it relies on the same temperature detection signal as the temperature control circuit, and it lacks redundancy in terms of safety.

(Object of the Invention) The present invention has been proposed in view of the above points, and its purpose is to provide a simple structure that can operate independently of the temperature control circuit, ensures reliable operation, and ensures safety. The object of the present invention is to provide a high temperature overheat prevention circuit.

(Disclosure of the Invention) The present invention will be described in detail below with reference to the drawings showing embodiments.

FIG. 1 is a circuit configuration diagram showing an embodiment of the present invention. To explain the configuration in the figure, 1 is a heater electrode connected to a commercial power supply AC through relay contacts ry ₁ and ry ₂ , main switch SW and both ends A and B of a temperature fuse TF, and 2 is a heater electrode that resists temperature changes. A temperature detection electrode facing the heater electrode 1 via an organic semiconductor having negative impedance characteristics,
One end of the temperature detection electrode 2 is connected to one end of the heater electrode 1 after passing through the core of the zero-phase transformer ZCT.

On the other hand, the secondary output of the zero-phase transformer ZCT is connected to an amplifier circuit 10, and the output of the amplifier circuit 10 is OR-inputted to the smoothing circuit 3 together with the output of the earth leakage detection circuit 7. Here, the smoothing circuit 3 rectifies and smoothes the input signal to convert it into DC, and its output is connected to the switching circuit 4 and the overheat prevention circuit 5, and the output of the switching circuit 4 is used to control the relay drive circuit. 8 is now working.

In addition, the off-time timer 6 is connected to the switching circuit 4.
This is to hold the output of the switching circuit 4 at a low level until a predetermined time has elapsed after the output signal of the switching circuit 4 becomes a low level.The reset input terminal R is connected to the output terminal of the switching circuit 4, and the output The terminal is connected to the input side of the switching circuit 4.

That is, when the output of the switching circuit 4 becomes low level, the relay contacts ry ₁ and ry ₂ are turned off, so that no commercial voltage is applied to the heater electrode 1 and no current flows to the temperature detection electrode 2.
This is to prevent the switching circuit 4 from being inverted again at this time. Further, 9 is a power supply circuit for supplying DC power to each circuit section.

In operation, when the temperature of the planar heating element is low, the impedance of the organic semiconductor is high, and the current flowing from the heater electrode 1 to the temperature detection electrode 2 via the organic semiconductor is small, so that the zero-phase transformer ZCT The voltage induced in the secondary winding of is a small value.

Therefore, the amplified output voltage of the amplifier circuit 10 is also small, and the signal converted into DC by the smoothing circuit 3 does not reach the comparison level of the switching circuit 4, so the relay drive circuit 8 turns on the relay contacts ry ₁ and ry _2. The heater electrode 1 is kept in this state, and electricity is continued to be applied to the heater electrode 1 to perform heating.

Next, when the temperature of the planar heating element reaches the set temperature, the switching circuit 4 operates in reverse and sends a signal to the relay drive circuit 8, turning off the relay contacts ry ₁ and ry ₂ and energizing the heater electrode 1. stop.

As the heater electrode 1 is disconnected from the commercial power supply AC, the leakage current flowing to the temperature detection electrode 2 disappears, and the switching circuit 4 tries to perform the inversion operation again, but it is turned off during the previous OFF operation. Since the timer 6 starts operating and keeps the relay drive circuit 8 off for a certain period of time, the contacts RY ₁ and RY ₂ do not turn on immediately, but instead cool down for a certain period of time set by the OFF time timer 6. It will turn back on again after a while. After that, repeat the above operation,
Therefore, the sheet heating element is kept at a constant temperature.

If some kind of circuit failure occurs and temperature control becomes impossible and the heater electrode 1 becomes continuously energized,
As the temperature of the heating element increases, the current flowing from the heater electrode 1 to the temperature detection electrode 2 increases.

At this time, the voltage detection circuit that operates the thyristor SCR is designed to prevent fluctuations in the temperature at which the thyristor SCR conducts without being affected by voltage fluctuations of the commercial power supply AC. That is, a voltage detection circuit consisting of a transistor Tr or the like is inserted between the temperature detection electrode 2 and the gate of the thyristor SCR, and a gate signal is applied from the collector of the transistor Tr to the thyristor SCR.

Specifically, the base of the transistor Tr is connected to the midpoint of a series circuit of resistors R ₄ and R ₅ connected in parallel with both ends of the heater electrode 1, and the collector is connected to _one end of the heater electrode 1 (thyristor The temperature detection electrode 2 is connected to the cathode side of the SCR and to the gate of the thyristor SCR, and to the emitter of the transistor Tr via a resistor _R7 .

However, the thyristor SCR is a transistor Tr.
By turning on, the gate signal is applied and the transistor Tr becomes conductive.For example, by appropriately selecting the ratio of resistors R ₄ and R ₅ , the base voltage of the transistor Tr can be changed.
If the voltage is set to 1.3V and the base-emitter voltage is 0.7V, the resistance will be
When the voltage applied to the emitter via _R7 reaches approximately 2V, the transistor Tr is turned on and a gate signal is given to the thyristor SCR.

On the other hand, if the voltage of the commercial power supply AC fluctuates, for example increases, the current flowing from the heater electrode 1 to the temperature detection electrode 2 increases, so the voltage of the temperature detection electrode 2 shows a high value for the same temperature. It turns out. However, since the base of the transistor Tr is provided with the voltage of the commercial power supply AC stepped down at a constant voltage division ratio by the resistors R ₄ and R ₅ ,
The base voltage also increases at the same rate as the above voltage increase, so the voltage at which the transistor Tr is turned on increases, making it possible to prevent fluctuations in operating temperature.

(Effects of the Invention) As described above, an organic semiconductor is disposed between a heater electrode and a temperature detection electrode, and a flow between the heater electrode and the temperature detection electrode is caused by a change in impedance of the organic semiconductor due to a change in temperature. In order to perform temperature control by detecting a change in current value and controlling energization to the heater electrode, one end of the temperature detection electrode is connected to one end of the heater electrode, and the other end of the temperature detection electrode is connected to one end of the heater electrode. It is connected to the gate of a switch element via a voltage detection circuit, and when the temperature rises abnormally, the switch element is turned on by the potential rise of the temperature detection electrode, and the operation of this switch element operates a cutoff circuit such as a temperature fuse. In the overtemperature rise prevention circuit configured to stop energization to the heater electrode, the voltage detection circuit is configured such that a voltage proportional to the commercial voltage is applied to the base, a collector is connected to the gate of the switch element, and a resistor is connected to the voltage detection circuit. The temperature detection electrode is constructed with a transistor connected to one end of the heater electrode through a resistor, and the other end of the temperature detection electrode is connected to the emitter of the transistor through another resistor, resulting in a simple configuration and operation independent of the temperature control circuit. The present invention has the effect of providing an overheating prevention circuit that is capable of performing the following steps, has reliable operation, and is highly safe.

[Brief explanation of drawings]

FIG. 1 is a circuit configuration diagram showing an embodiment of the present invention;
FIG. 2 is a circuit configuration diagram showing a conventional temperature control circuit. 1... Heater electrode, 2... Temperature detection electrode, 3...
... Smoothing circuit, 4 ... Switching circuit, 5 ... Overheat prevention circuit, 6 ... Off time timer, 7 ... Leakage detection circuit, 8 ... Relay drive circuit, 9 ... Power supply circuit, 10 ... Amplification circuit , AC...commercial power, SW
...Main switch, ZCT...Zero phase transformer,
ry ₁ , ry ₂ ...Relay contact, TF...Temperature fuse,
SCR...Thyristor, _R3 to _R7 ...Resistor.

Claims (1)

[Claims] 1. An organic semiconductor is disposed between a heater electrode and a temperature detection electrode, and the value of the current flowing between the heater electrode and the temperature detection electrode is controlled by an impedance change of the organic semiconductor caused by a change in temperature. In order to perform temperature control by detecting a change and controlling energization to the heater electrode, one end of the temperature detection electrode is connected to one end of the heater electrode, and the other end of the temperature detection electrode is connected to a voltage detection circuit. The switch element is connected to the gate of the switch element through the heater electrode, and when the temperature rises abnormally, the switch element is turned on by the potential rise of the temperature detection electrode, and the operation of this switch element operates a cutoff circuit such as a temperature fuse, and the switch element is connected to the heater electrode. In the overtemperature rise prevention circuit configured to stop energization of the voltage detection circuit, a voltage proportional to the commercial voltage is applied to the base of the voltage detection circuit, and the collector is connected to the gate of the switch element and connected to the heater through a resistor. 1. An overtemperature rise prevention circuit comprising a transistor connected to one end of an electrode, the other end of the temperature detection electrode being connected to the emitter of the transistor via another resistor.