JPS5830088A - Safety protecting circuit for electric heater - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

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, etc., as shown in the front view in Fig. 1, a heat-sensitive resistor 10 made of polyamide-based resin or the like having negative temperature-impedance characteristics is coated with aluminum foil or the like on one side. Heat sensitive electrode 2
At the same time, a patterned heater 3 is placed on the other side of the heat-sensitive resistor 1, and an insulating film 1 is placed on both sides.
A heat-sensitive element 5 formed by being covered with lumens 4, 4 is employed.

This heat-sensitive cable 5 is connected to a power supply 6 VC via a power supply path to constitute a -C heater circuit, and this heater circuit is shown in FIG.
Is it @ degree according to the circuit configuration I/C shown? 111# will be sent.

A constant AC tAL voltage 1d is input to the input section of the input/output circuit 7, and the input voltage is divided between the -11+ e-pedance element included in this input section and the heat-sensitive cable 5,
The feeling of this heat-sensitive cord 5? The PJ resistor 1 applies a partial voltage corresponding to yx<-r impedance to the heat-sensitive pole 211C, and generates an impedance change as an output voltage change, and generates an impedance change as an output voltage change. The temperature is detected by the temperature detection circuit 8 via the output part of the output circuit 7, and the detected value is compared with a reference value given corresponding to a predetermined set temperature by the next stage switching circuit 9, and a comparison judgment output is produced. The transistor 10 in the next stage is turned on and off, and the north relay excitation coil 11 connected in series with this transistor 10 is controlled to be driven to control the relay contact 11a.
.

By the on/off operation of 11a, the power supply path of the heater circuit is connected/disconnected and the temperature is controlled. In FIG. 2, 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.

The heater 3 may be damaged due to an electrical leakage accident in such an electric heating device or contact fusion of the relay contacts 11 a r 11 m.
As a countermeasure against abnormal heating, conventionally, as shown in the figure, the detection value of the temperature detection circuit 8 is compared with a predetermined reference value corresponding to abnormal heating in an overtemperature prevention circuit 14 to obtain an abnormal temperature rise detection output. Thyristor 15 separately connected in parallel to the power source 6
The switching circuit 16 consisting of the above-mentioned abnormal temperature rise detection output is turned on, and the heat of the heat generating resistor 17 inserted into the switching circuit 16 fuses the temperature fuse 18 to urgently interrupt the power supply line. While constituting a prevention mechanism, an earth leakage detection circuit 19 is separately provided to detect earth leakage accidents, 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 current supply. This has a configuration in which two protection circuits are installed in parallel in addition to the control circuit, which has the disadvantage of not only complicating the configuration but also increasing cost.

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 constructed by diodes 19a, 19b and a current limiting resistor 20 between each power supply path and the heat-sensitive II pole 2 of the heat-sensitive element 5, as compared to the conventional electric heating device. Connect the branch circuit 21 (each diode 19a, 19b is branch-connected from the heat-sensitive electrode non-connected side of a current limiting resistor of 2°, and each diode 19a, 19b is connected to each power supply path in the same connection direction). A current transformer 22 for detecting the current flowing through this common circuit is disposed in the common circuit in which the current limiting resistor 20 of this branch circuit 21 is inserted, while a current transformer 22 for detecting the current flowing through the common circuit is arranged, A thyristor 23 is connected between the detected value input terminal e of the switching circuit 9 and the power supply path.
Next, the earth leakage detection circuit 24 is configured, and the detection output of the current transformer 22 is amplified by the 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 amplification circuit 24 is configured. The output of the circuit 25 is
The heating resistor 7 which blows out the temperature fuse 18 is input as a gate trigger signal to the thyristor 15 of the switching circuit 16, and the switching circuit 1
6 is made to function as an overtemperature prevention circuit.

In this embodiment, each diode 19 of the branch circuit 21
Although the cathodes of both diodes 19a and 19b are connected to the power supply path, the anode sides of the diodes 19a and 19b may be connected to the power supply path.

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

The operation of the safety protection circuit of this electric heating device will be explained next.

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 the case of normal temperature control. , for example, the heating surface is 100
``When it rises to C, its impedance is approximately 1
It is known that the value drops to 7100 or more.

Therefore, in the electric heating device, the relay contacts 11a, l
When contact fusion occurs in contact fusion of relay contact 11a and lla, and the on/off control of relay contacts 11a and lla by the switching path 9 no longer works, and the temperature rises abnormally, the heat-sensitive resistor 1 tL flows compared to the case of normal use. The current increases rapidly, and the increase in current flows through the current transformer 22 disposed 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, and the heating action of the heating resistor 17 melts down the temperature voltage 18 to turn on the heater. The circuit's power supply path is completely cut off, avoiding abnormal temperature rise accidents.

In addition, in the case of an electric leakage accident in which a conductor pin or the like is placed over the heat-sensitive electrode 2 and a human body touches the conductor bottle, causing a leakage current to flow through the human body to the ground, the heat-sensitive cord 5
//i Since it is grounded through the human body resistance (approximately 300Ω, which is much smaller than the heat-sensitive resistor l), the temperature rises to 50°C.
A much larger current flows through the heat-sensitive element 5 than in the case of the temperature setting, and the current transformer 22 detects this as in the case of the abnormal temperature rise, and the detection signal is amplified and output from the amplifier circuit 25. The earth leakage detection circuit 24 is turned on, and the voltage level of the detection value input terminal (■) of the switching circuit 9 is held at a low level corresponding to the case of abnormal temperature rise, and the switching circuit 9 turns off the power supply path of the heater circuit. is held and the flow to the heater circuit [2>E is urgently stopped.

With this configuration, the detection section can be shared by one circuit configuration to provide two functions of leakage detection and abnormal temperature rise detection, which simplifies the circuit configuration.

Manufacturing costs can be reduced.

As described above, the safety waist circuit of the electric heating device of this invention is
A heat-sensitive element having a heat-sensitive resistor having temperature-impedance characteristics, 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 detection by the detection circuit. a switching circuit that turns on and off the heater circuit by comparing the value with a predetermined reference value;

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. Warm fc includes a current transformer that detects the entire energization #L of the branch circuit that increases in the event of a current leakage, a current leakage detection circuit that receives the detection output of the current transformer and maintains the switching circuit in the OFF operation side, and the transformer. The device is equipped with an overtemperature prevention circuit that receives the detection output from the heater circuit and immediately shuts off the heater circuit, so the detection part can be shared in one circuit configuration and can be used for two functions: abnormal temperature rise detection and earth leakage detection. It has the following effects: functions can be added at the same time, the configuration is simple, and manufacturing costs can be reduced.

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional view of a heat-sensitive element, Fig. 2 is a circuit diagram showing a conventional example, and Fig. #I3 is a circuit diagram showing an embodiment of the present invention.

Claims (1)

[Claims] A heat-sensitive element having a heat-sensitive resistor having temperature-impedance characteristics, 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 detection by the detection circuit. a switching circuit that turns on/off the heater circuit by comparing the 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 consisting 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 electricity, and a detection output of the current transformer. A safety protection circuit for an electric heating device, comprising: a leakage detection circuit for holding the switching circuit in the OFF operation side; and an overhumidity prevention circuit for urgently shutting off the heater circuit in response to the detection output of the current transformer.