JPS643313B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a safety protection circuit for electric heating devices such as electric carpets.

Conventionally, as an electric heating device installed in a carpet or the like, as shown in the cross-sectional view in FIG. A heat-sensitive element 5 is adopted in which a heat-sensitive electrode 2 is stretched, a patterned heater 3 is stretched on the other side of the heat-sensitive resistor 1, and both surfaces are further covered with insulating films 4, 4. ing.

This heat-sensitive element 5 is connected to a power source 6 via a power supply line to constitute a heater circuit, and the temperature of this heater circuit is controlled by the circuit configuration shown in FIG.

A predetermined AC voltage signal is input from the input section of the input/output circuit 7, and the input voltage is divided between the impedance element included in this input section and the heat-sensitive element 5, and the heat-sensitive resistor 1 of the heat-sensitive element 5 is A partial voltage corresponding to the impedance shown is applied to the heat-sensitive electrode 2 to generate a change in the impedance of the heat-sensitive resistor 1 due to a temperature change as an output voltage change, and this output voltage is outputted via the output section of the input/output circuit 7. The temperature detection circuit 8 detects the temperature, and the next-stage switching circuit 9 compares the detected value with a reference value given in correspondence with a predetermined set temperature.The comparison judgment output turns on and off the next-stage transistor 10. Drive off,
The drive of the relay excitation coil 11 connected in series to this transistor 10 is controlled, and the relay contact 11
The on/off operation of a and 11a connects and disconnects the power supply path of the heater circuit, thereby controlling the temperature. Second
In the figure, 12 is an oscillation circuit that supplies a predetermined AC voltage signal to the input section of the input/output circuit 7, and 13 is a DC power supply circuit for driving the oscillation circuit 12.

As a countermeasure against abnormal heating of the heater 3 due to a leakage accident in such an electric heating device or contact fusion of the relay contacts 11a, 11a, conventionally, as shown in the figure, the detected value of the temperature detection circuit 8 is set to prevent overheating. A circuit 14 compares it with a predetermined reference value corresponding to abnormal heating to obtain an abnormal temperature rise detection output, and separately turns on a switching circuit 16 consisting of a thyristor 15 connected in parallel to the power supply 6 with the abnormal temperature rise detection output. , constitutes an overtemperature prevention mechanism in which the temperature fuse 18 is fused by the heat of the heating resistor 17 inserted in this switching circuit 16 and the power supply path is cut off in an emergency manner, while separately detecting an electric leakage accident. An earth leakage detection circuit 19 is provided, and the detection output of this earth leakage detection circuit 19 is used to stop the operation of the switching circuit 9 and stop the energization.It has a configuration in which two protection circuits are installed in parallel in addition to the temperature control circuit. This has the disadvantage that not only the configuration is complicated but also the cost is high.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a safety protection circuit for an electric heating device that has a simple configuration in which the detection section is configured as one circuit and is used for both earth leakage detection and overtemperature prevention.

An embodiment of this invention is shown in FIG. That is, the safety protection circuit of this electric heating device is different from that of the conventional electric heating device in that it connects each power supply path and the heat-sensitive element 5.
Diodes 19a, 19b are connected between the heat-sensitive electrode 2 of
and a current limiting resistor 20 (each diode 1 is connected from the non-connected side of the current limiting resistor 20 to the heat sensitive electrode
9a and 19b are branch-connected, and each diode 19
a, 19b are connected to each power supply path in the same connection direction), and a current transformer is connected to the common circuit in which the current limiting resistor 20 of this branch circuit 21 is inserted to detect the current flowing through this common circuit. 22, a thyristor 23 is connected between the detection value input terminal of the switching circuit 9 into which the detection value of the temperature detection circuit 8 is input and the power supply line to constitute the earth leakage detection circuit 24. The detection output of the current transformer 22 is amplified by an amplifier circuit 25, and the amplified output is used as a trigger signal to turn on the earth leakage detection circuit 24, and at the same time, the output of the amplifier circuit 25 is used to generate heat that blows the temperature fuse 18. resistance 1
Thyristor 15 of switching circuit 16 including 7
The switching circuit 16 is configured to be inputted as a gate trigger signal to the switching circuit 16 to function as an overtemperature prevention circuit.

In this embodiment, the cathodes of the diodes 19a and 19b of the branch circuit 21 are both connected to the power supply path;
The anode side of 9b may be connected to the power supply path.

In the figure, a series circuit of a resistor 26, a variable resistor 27, and a resistor 28 is a voltage dividing circuit that provides a comparison reference value for the switching circuit 9.

Next, the operation of the safety protection circuit of this electric heating device will be explained.

For example, when a polyamide resin is used as the heat-sensitive resistor 1 of the heat-sensitive element 5, its temperature-impedance characteristic exhibits an extremely negative characteristic, compared to the maximum temperature of 50°C in normal temperature control. For example, when the heating surface rises to 100℃,
It is known that the impedance decreases to about 1/100 or more.

Therefore, in the electric heating device, the relay contact 1
1a and 11a cause contact fusion, and the switching circuit 9 turns on and off the relay contacts 11a and 11a.
When the OFF control stops working and the temperature rises abnormally, the current flowing through the heat-sensitive resistor 1 increases rapidly compared to the case during normal use, and this increase in current flows through the changer installed in the branch circuit 21. The detection output is amplified by the amplifier circuit 25, and the amplified output turns on the switching circuit 16 as a gate trigger signal to turn on the heating resistor 1.
The temperature fuse 18 is blown by the heat generating action of 7, and the power supply path of the heater circuit is completely cut off, thereby avoiding an abnormal temperature rise accident.

Furthermore, in the case of an electrical leakage accident where a conductor pin or the like is inserted into the heat-sensitive electrode 2 and a human body touches this conductor pin, causing a leakage current to flow through the human body to the ground, the conductor pin may connect the heat-sensitive electrode 2 and the heater. As a result, a much larger current flows through the heat-sensitive element 5 than in the case of the temperature setting of 50°C, which is transferred to the current transformer 2 as in the case of abnormal temperature rise.
The leakage detection circuit 24 is turned on by the detection signal detected by the switch 2, amplified and outputted from the amplifier circuit 25, and the voltage level at the detection value input terminal of the switching circuit 9 becomes a low level corresponding to an abnormal temperature rise. The power supply path of the heater circuit is held in the OFF state by the switching circuit 9, and the power supply to the heater circuit is urgently stopped. With this configuration, the detection unit can be shared in one circuit configuration to provide two functions: earth leakage detection and abnormal temperature rise detection.
The circuit configuration is simplified and manufacturing costs can be reduced.

As described above, the safety protection circuit for an electric heating device of the present invention includes a heat-sensitive element in which a heat-sensitive electrode is stretched on one side of a heat-sensitive resistor having temperature-impedance characteristics and a heater is placed in contact with the other face, and the heat-sensitive resistor has a temperature-impedance characteristic. a detection circuit that detects a change in impedance of the body; a switching circuit that compares a value detected by the detection circuit with a predetermined reference value and turns on and off the heater circuit;
A branch circuit consisting of a current-limiting resistor whose one end is connected to the heat-sensitive electrode, a pair of diodes branch-connected in the same connection direction between the other end of the current-limiting resistor and each power supply path, and an abnormal rise in the heater. a current transformer that detects the current flowing through the branch circuit that increases when the temperature or current leakage occurs; and a current leakage detection circuit that receives the detection output of the current transformer and maintains the switching circuit in an OFF operation side;
Since it is equipped with an overtemperature prevention circuit that urgently shuts off the heater circuit in response to the detection output of the current transformer, the detection section is shared in one circuit configuration and can be used for both abnormal temperature rise detection and earth leakage detection. It has the advantage of being able to provide two functions at the same time, simplifying the configuration, and reducing manufacturing costs.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a heat-sensitive element, FIG. 2 is a circuit diagram showing a conventional example, and FIG. 3 is a circuit diagram showing an embodiment of the present invention. DESCRIPTION OF SYMBOLS 1... Heat sensitive resistor, 2... Heat sensitive electrode, 3... Heater, 5... Heat sensitive element, 6... Power supply, 7... Input/output circuit, 8... Temperature detection circuit, 9... Switching circuit, 10 ...Transistor, 11...Relay excitation coil, 11a...Relay contact, 15...Thyristor, 16...Switching circuit (overtemperature prevention circuit), 17...Heating resistor, 18...Temperature fuse, 19a, 19b... ...Diode, 20...Current limiting resistor, 21...Branch circuit, 22...Current transformer, 2
3... Thyristor, 24... Leakage detection circuit, 25
...Amplification circuit.

Claims (1)

[Claims] 1 A heat-sensitive element having a heat-sensitive resistor having a temperature-impedance characteristic, a heat-sensitive electrode stretched on one side and a heater placed in contact with the other face, a detection circuit for detecting an impedance change of the heat-sensitive resistor, and a detection circuit according to the present invention. a switching circuit that turns on and off the heater circuit by comparing the detected value with a predetermined reference value; a current limiting resistor having one end connected to the heat-sensitive electrode; and a connection between the other end of the current limiting resistor and each power supply path. a branch circuit made up of a pair of diodes branch-connected in the same direction; a current transformer that detects a current flowing through the branch circuit that increases when the heater abnormally rises in temperature or leaks;
An electric heating device comprising: a leakage detection circuit that receives a detection output from the current transformer and holds the switching circuit in an OFF operation side; and an overtemperature prevention circuit that receives a detection output from the current transformer and immediately shuts off a heater circuit. Equipment safety protection circuit.