JPH1038298A - Protector for electric heating instrument - Google Patents

Abstract

PROBLEM TO BE SOLVED: To simplify a fusion detecting circuit and a disconnection detecting circuit is particular by a method wherein the abnormal overheating of a heater due to the fusion of a relay contact is prevented and the disconnection of the heater is detected immediately to shut off a main circuit. SOLUTION: A protector for an electric heating instrument is provided with a series circuit of a relay contact 13, connected in series to a heater 6, and a temperature fuse 14, a heating resistor 16, provided near the temperature fuse, a relay contact fusion detecting line 39 and a disconnection of heater detecting line 31. In such a protector, the heating resistor is controlled so as to generate heat to cut the temperature fuse by fusion and shut off a main circuit in either case of the fusion of the relay contact or the disconnection of the heater.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a safety device for an electric heating device for heating, such as an electric carpet.

[0002]

2. Description of the Related Art A heater used for an electric carpet has a power consumption of about 800 W to 1000 W, and it is inconvenient to control the duty ratio by a semiconductor control element such as SCR or TRIAC. . As a specific reason, in the case of a semiconductor control element, although the conduction angle can be controlled, a large allowable current cannot be taken out. If the allowable current is increased, the area of the heat radiator must be increased by a power, and the heat radiator becomes large, which is not suitable for household appliances.

[0003] For this reason, a small relay having a relatively large allowable current is used for controlling the heater of the electric carpet.

[0004] In addition, a heater used particularly for an electric carpet must be slender and capable of withstanding bending. However, the heater may be deteriorated over time or may not be able to withstand bending, resulting in disconnection.

[0005]

However, in the use of the above-mentioned relay, the contact material of the relay contact deteriorates and the welding occurs due to the long-term use, and the relay contact should be opened (OFF). Nevertheless, since the heater continues to be closed (ON) and the temperature of the heater becomes high, which is very dangerous, for example, as shown in Japanese Patent Application Laid-Open No. 63-113232, a heating resistor is generated during welding to connect the heater in series. The blown thermal fuse is blown to cut off the main circuit.

As a countermeasure against disconnection of the heater, Japanese Unexamined Utility Model Publication No. 2-31214 discloses a method. However, when the heater is completely disconnected and a large distance is generated between the ends of the disconnection, the main result is obtained. There was no problem with the circuit being interrupted, but when the distance between the ends immediately before or after the disconnection was small, sparks were generated due to contact and separation of the ends of the disconnection, which became dangerous.

[0007] A dedicated circuit is separately provided for the above-described safety circuit by welding of the relay contacts and the safety circuit by disconnection of the heater. was there.

The present invention is intended to prevent abnormal overheating of a heater due to welding of a relay contact and to immediately detect a break in the heater to prevent a spark between the broken ends. The circuit is simplified by sharing with the disconnection detection circuit.

[0009]

SUMMARY OF THE INVENTION The present invention comprises a heater, a relay contact connected in series to the heater, a first switching element connected in series to a relay for opening and closing the relay contact, and a first switching element in a normal state. A second switching element that conducts and non-conducts in conjunction with the switching element; a temperature control circuit that detects the temperature of the heater to control the first switching element; and a series circuit of a series circuit of the heater and the relay contact. A series circuit of a thermal fuse connected to the relay, a heating resistor provided in the vicinity of the thermal fuse connected in parallel to a series circuit of the heater and the relay contact, and a series circuit of an opening / closing element that conducts by conduction of the second switching element; A welding detection line connected to an AC power supply side of the contact and a conduction signal providing path of the second switching element; one side of the heater and a first switch; And a disconnection detection line connected to the conduction signal application path of the switching element. When the relay contact is welded, the potential of the welding detection line and the potential of the disconnection detection line on the trigger side of the second switching element are equalized. When the heater is disconnected, the trigger signal from the disconnection detection line is stopped, and in any case, the second switching element is turned off, the switching element is turned on, and the thermal fuse is turned off by the heating resistor. It will blow.

[0010]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view showing an embodiment of the present invention in which a safety device for an electric heater is mounted on an electric carpet. FIG. 1 is an electric circuit diagram of an electric carpet according to an embodiment of the present invention, FIG. 2 is a plan view of a carpet body, FIG. 3 is an explanatory diagram of a heater wire, and FIG. 4 is an explanatory diagram of a temperature protector. .

(1) is a rectangular carpet body, in which a heater wire (2) and a temperature detection wire (3) are arranged in a meandering manner, and a controller (4) is provided at a corner portion.

As shown in FIG. 3, the heater wire (2) includes an insulating core (5), a heater (6) spirally wound outside the insulating core, and a predetermined temperature provided outside the heater. It comprises an insulating layer (7) that melts as described above, a short-circuit wire (8) spirally wound around the outside of the insulating layer, and a jacket (9) that insulates the outside of the short-circuit line.

The temperature detecting wire (3) includes two conductive wires (10) (10) having both ends short-circuited, and a temperature-sensitive layer (1) having an impedance that changes depending on temperature provided between the conductive wires.
1) and a core material (not shown) for winding the inner conductor and a jacket for insulating the outer conductor.

(12) is a commercial AC power supply, and (13) is a relay (28) described later connected to one end of the heater (6).
This series circuit is connected between both poles of an AC power supply via a thermal fuse (14).

As shown in FIG. 4, the thermal fuse (14) has two heating resistors (15) and (16) closely attached to the outside thereof, and constitutes a main circuit interrupting device (17) as a whole. .

(18) is a temperature detection circuit connected to the conductor (10), (19) is a reference circuit serving as a base for setting the carpet body (1) to a desired temperature, and (20) is the temperature detection circuit. This is a comparison circuit for comparing the value of (18) with the value of the reference circuit (19). The temperature detection circuit (18), the reference circuit (19), and the comparison circuit (20) include a temperature control circuit (2).
Construct 1).

(22) is a first diode connected to the pole (A) of the AC power supply (12), and (23) is a first diode connected to the first diode.
A second diode connected in series with one heating resistor (15) in the opposite direction to the diode (22), and (24) is a third diode connected in series with one heating resistor (15). The second diode (23)
And a series circuit of one of the heating resistors (15) are connected to the AC power supply (12) via the first diode (22) and the thermal fuse (14).

(25) a fourth diode having a cathode connected to one end of the short-circuit line (8) and arranged in a direction opposite to the third diode (24), and an anode connected to one end of the other heating resistor (16); Connected to The other heating resistor (1
The other end of 6) is connected to the connection between the first diode (22) and the second diode (23).

(26) is connected between a connection between the anode of the fourth diode (25) and one end of the other heating resistor (16) and the pole (B) of the AC power supply (12), and is connected to the first diode (25). 22) Switching element (hereinafter referred to as SCR)
And).

The cathode of the SCR (26) is connected to the contact on the pole (B) side of the AC power supply (12), which is different from the contact on the connection side of the relay contact (13) with the heater (6).

(27) is one of the heating resistor (15) and the third
A relay power supply circuit connected to a connection portion with the diode (24), and a relay (28) that uses a voltage obtained by the relay power supply circuit as a drive power supply and opens and closes the relay contact (13).

Reference numeral (29) denotes a first switching element comprising a transistor for controlling the relay (28), a collector connected to the relay (28), and an emitter connected to the heater (5) via a resistor (30). The emitter is connected to a connection with the contact (13), and the connection line of the emitter constitutes a disconnection detection line (31) of the heater (5).

(32) and (33) are resistors and capacitors, and the gate trigger circuit (34) of the SCR (26).
Is configured. (35) is a protection diode of the SCR (26), and (36) is a gate resistor.

(37) a second switching element comprising a transistor which conducts and non-conducts in cooperation with the first switching element (29) in a normal state, and has a collector connected through resistors (38) and (36). The SCR (26)
, And the emitter is connected to a contact on the pole (B) side of the AC power supply (12) which is different from the contact on the connection side of the relay contact (13) with the heater (6).

This emitter connection line forms a welding detection line (39) for the relay contact (13).

(40) and (41) are a resistor and a diode connected between the base and the emitter of the second switching element (37).

Next, the operation will be described. First, a normal state will be described. Since the temperature of the carpet body (1) is low at the initial stage of energizing the heater (6), the temperature-sensitive layer (11)
The temperature detection circuit (18) which detects the resistance value converts the resistance value into a voltage value and outputs the converted voltage value. However, the difference from the output voltage of the reference circuit (19) is large, and the comparison circuit (18) 20) supplies a bias current to the base of the first switching element (29) to make the first switching element conductive.

The relay (28) is driven by the conduction of the first switching element (29), and the relay contact (13)
Is closed and an AC voltage is applied to the heater (6), and the heater continues to generate heat.

By the conduction of the first switching element (29), a bias current flows to the base of the second switching element (37), and the second switching element is also made conductive, so that the capacitor of the gate trigger circuit (34) is turned on. Absorb the voltage between both ends of (33) and apply the SCR (26)
And the other heating resistor (16) does not generate heat.

Also, the current from each of the poles (A) and (B) of the AC power supply (12) is supplied to the first diode (22) and the second and third diodes (2).
3) and (24), it does not flow and does not generate heat.

Eventually, when the temperature of the carpet body (1) rises and reaches the set temperature, the output of the comparison circuit (20) disappears, the first switching element (29) becomes non-conductive, and the relay (28) is removed. Energized to open the relay contact (13) and cut off the power supply to the heater (6).

With the opening of the relay contact (13), the second switching element (37) is driven by a current flowing from the pole (A) of the AC power supply (12) through the heater (6) through the disconnection detection line (31). Conducts and the condenser (33)
And the non-conductive state of the SCR (26) is continued.

When the temperature of the carpet body (1) drops, an output is generated from the comparison circuit (20), and the first switching element (29) is turned on again to turn on the relay (28).
Is driven to close the relay contact (13) and energize the heater (6).

The above operation is repeated to control the carpet body (1) to the set temperature.

Thus, when the relay contact (13) is welded due to long-term use of the carpet body (1) or due to some other factor, the carpet body (1) is welded.
Is higher than the set temperature, there is no output from the comparison circuit (20), and the first switching element (29) is non-conductive. At this time, in a normal state, as described above, the base potential of the second switching element (37) is high and the second switching element (37) is conductive and the SCR (26) is non-conductive. As a result, the base potential and the emitter potential of the second switching element (37) become the same, and this element becomes non-conductive.

From this, the gate trigger circuit (3
4) Voltage of condenser (33) is not absorbed and SCR
(26), and the current flowing from the pole (A) of the AC power supply (12) flows through the first diode (22), the other heating resistor (16), and the SCR (26). It flows to the pole (B) of 12).

The conduction of the SCR (26) causes the other heating resistor (16) to generate heat, blow the thermal fuse (14), cut off the main circuit, and cut off the power to the heater (6).

Further, if a break occurs in a part of the heater (6) due to an increase in the number of bendings of the carpet body (1) or deterioration over time, the bias current due to the break detection line (31) disappears and the second switching element. (37) becomes non-conductive, the SCR (26) becomes conductive, and the other heating resistor (1)
6) generates heat and blows the thermal fuse (14) to cut off the main circuit.

As described above, the second switching element (37), the SCR (26), the other heating resistor (16) and the temperature fuse (14) are connected to the welding detection circuit and the heater (6) when the relay contact (13) is welded. ) Is shared with the disconnection detection circuit at the time of disconnection.

Further, the relay contact (13) is continuously closed due to a failure or short circuit of the temperature detecting circuit (18), the reference circuit (19) and the comparing circuit (20) or the first switching element (29). In the abnormal state, the heater (6) continuously generates heat and the insulating layer (7) melts in an abnormally overheated state. For example, the insulating layer (7) melts at a point a shown in FIG. In this case, the current flowing from the pole (A) of the AC power supply (12) is the first diode (22), the other heating resistor (16), the fourth diode (25), the short-circuit line (8), the short-circuit portion ( a), flows to the pole (B) via the relay contact (13). Therefore, the other heating resistor (16)
Generates heat and blows the thermal fuse (14) to cut off the main circuit.

Further, for example, when the heater (6) and the short-circuit line (8) are melted and short-circuited at the point b shown in FIG. 1, the current flowing from the pole (B) of the AC power supply (12) is equal to the third diode. (24), it flows to one of the heating resistors (15), the short-circuit line (8), the short-circuit portion (b), and the pole (A). Therefore, one of the heating resistors (15) generates heat, blows the thermal fuse (14), and cuts off the main circuit.

Therefore, the other heating resistor (16) and thermal fuse (14) are connected when the above-mentioned relay contact (13) is welded, when the heater (6) is disconnected, and when the heater (6) and the short-circuit wire (8) are connected. It functions as a safety device in the event of a short circuit.

[0043]

As described above, the present invention uses a heating resistor and a thermal fuse for interrupting the main circuit when detecting welding of a relay contact and when detecting disconnection of a heater. It is not necessary to separately provide a safety circuit for detecting welding and a safety circuit for disconnection of the heater. This simplifies the circuit, reduces the size of the circuit board, and is highly versatile.

[Brief description of the drawings]

FIG. 1 is an electric circuit diagram of an electric carpet described as an embodiment of a safety device for an electric heating tool according to the present invention.

FIG. 2 is a plan view of the carpet body.

FIG. 3 is an explanatory diagram of a heater wire.

FIG. 4 is an explanatory view of the temperature protector.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Carpet body 6 Heater 12 AC power supply 13 Relay contact 14 Thermal fuse 15 Heating resistor 16 Heating resistor 21 Temperature control circuit 26 Switching element (SCR) 28 Relay 29 1st switching element 31 Disconnection detection line 37 2nd switching element 39 Welding detection line

Claims (1)

[Claims] 1. A heater, a relay contact connected in series to the heater, a first switching element connected in series to a relay that opens and closes the relay contact, and in a normal state, connected to the first switching element to conduct. Second to conduct non-conduction
A switching element, a temperature control circuit that detects the temperature of the heater and controls the first switching element, a temperature fuse connected in series to a series circuit of the heater and the relay contact, and a series of the heater and the relay contact. A series circuit of a heating resistor provided in the vicinity of the thermal fuse connected in parallel with a circuit and an opening / closing element which is made conductive by conduction of the second switching element; an AC power supply side of the relay contact and a conduction signal of the second switching element A welding detection line connected to the application path, and a disconnection detection line connected to one side of the heater and a conduction signal application path of the first switching element. When the potential of the welding detection line and the potential of the disconnection detection line on the trigger side are the same, and the heater is disconnected An electric heating tool, wherein a trigger signal by a disconnection detection line is stopped, the second switching element is turned off in any case, the switching element is turned on, and the thermal fuse is blown by a heating resistor. Security equipment.