JPH08129945A - Contact point welding protective device of heater control circuit - Google Patents

Abstract

PURPOSE: To speedily and reliably stop current-carrying to a heating heater when a contact point of a relay is welded. CONSTITUTION: When a contact point 2A is turned on when a driving signal is not sent out of a control device 18, a contact point welding detecting circuit 41 outputs a contact point welding signal. Therefore, a thyristor 4 is turned on, and an electric power supply circuit breaker 9 operates, and current-carrying to a heating heater 3 is speedily stopped. Since the contact point welding detecting circuit 41 is arranged separately from the control device 18, even if the control device 18 makes a malfunction, welding of the contact point 2A of a relay 2 can be reliably detected.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heater control circuit for controlling the ON / OFF of a heating heater by opening / closing a contact of a relay, and detecting the welding of the contact of the relay to cut off the power supply. The present invention relates to a contact welding protection device for a heater control circuit.

[0002]

2. Description of the Related Art Generally, a series circuit of a heater for heating and a contact of a relay is connected between power supply lines, and the contact of the relay is opened / closed by a drive signal from a control means to control the on / off of the heater for heating. This type of heater control circuit is used in home electric appliances such as electric pots. However, in such a heater control circuit, when the contacts of the relay connected in series with the heating heater are welded, the heating heater is continuously energized, causing abnormal overheating inside the pot body, which causes thermal deformation. The pot body could be damaged.

In order to solve such problems, various methods such as the following have been conventionally proposed. For example,
In Japanese Patent Publication No. 4-44532, a contact of a drive relay for turning on and off a heater for heating is closed and latched in an on state due to a malfunction of an electronic component constituting a relay drive circuit (that is, for drive). When the relay is in the same state as welding, the current flowing to the heating heater is detected by a current detection circuit such as a current transformer, and the heating heater is used regardless of whether the drive signal to the coil of the drive relay is off. It is disclosed that the contact of the breaking relay connected in series with the contact of the heater for heating and the contact of the driving relay is forcibly turned off when the power is being supplied to the heater.

Further, in Japanese Patent Laid-Open No. 3-89425 and Japanese Patent Laid-Open No. 60-254530, when the welding of the contacts of the relay is detected, a pulse signal, that is, ON / OFF repetition from the control means to the relay drive circuit is detected. It is disclosed that a signal is applied to vibrate the contacts and the lightly welded contacts are separated so as to extend the life.

Further, in Japanese Patent Laid-Open No. 59-194324, a temperature control device, which is a thermistor, detects a temperature rise of a heater for heating, and a drive signal to a relay is not output, but a heater for heating is not used. When the temperature of the heater is rising, the contacts are vibrated to separate the lightly welded contacts, and the life extension effect is also aimed at.

[0006]

In the above-mentioned prior art, the one disclosed in Japanese Patent Publication No. 4-44532 is as follows.
The configuration of the current detection circuit for detecting the current supplied to the heating heater becomes complicated and expensive, and if there is a malfunction in this portion, the breaking relay may not function reliably. Further, not only the drive relay but also the drive signal for the breaking relay is controlled by the microcomputer, which is the control means, based on the current detection signal from the current detection circuit. However, the disconnecting relay may not operate properly when the drive relay is welded.

On the other hand, JP-A-3-89425, JP-A-60-254530 and JP-A-59-194.
In all of the devices described in Japanese Patent No. 324, the energization of the heater cannot be immediately stopped at the time when the contacts are welded, and the basic safety cannot be ensured.

In view of the above problems, the present invention provides a contact welding protection device for a heater control circuit that can quickly and surely stop energizing the heating heater when the relay contacts are welded. That is the purpose.

[0009]

According to another aspect of the present invention, there is provided a contact welding protection apparatus in which a series circuit of a heater for heating and a contact of a relay is connected between power supply lines, and a drive signal from a control means controls the relay. In a heater control circuit for opening and closing a contact to control the heating and breaking of the heating heater, the presence or absence of a drive signal from the control means and the open / closed state of the contact of the relay are monitored, and when the contact of the relay is welded. A contact welding detection circuit provided independently of the control means for outputting a contact welding detection signal, a power breaker for cutting off power supply from the power supply line to the heating heater, and a contact welding detection circuit And a drive circuit breaker driving circuit for operating the power breaker according to a contact welding detection signal.

Further, in the contact welding protection apparatus according to the second aspect of the present invention, the temperature fuse for cutting off the power supply and the resistor for melting the temperature fuse by heating when the contact of the relay is welded are integrally molded. The power supply circuit breaker.

[0011]

According to the structure of claim 1, if the contact of the relay is kept on when the drive signal is not output from the control means, the contact welding detection circuit detects this state and immediately drives the power breaker. Outputs a contact welding signal to the circuit. As a result, the power breaker operates and the power supply to the heating heater is immediately stopped. Further, since the contact welding detection circuit is provided separately from the control means that outputs the drive signal,
Even if the control means malfunctions, the welding of the contacts of the relay can be surely detected, and the power supply to the heating heater can be quickly interrupted in an emergency.

According to the second aspect of the present invention, if the fusing temperature of the thermal fuse and the resistance value of the heating resistor are arbitrarily selected in advance, the time until the thermal fuse is blown can be easily changed.

[0013]

Embodiments of the present invention will be described below with reference to the accompanying drawings. Each of the circuit configurations shown in these embodiments is applied to an electric pot which is a kind of household electric products.

First, in FIG. 1 showing the first embodiment of the present invention, reference numeral 1 is a commercial AC power source which is, for example, an AC 100V power source. 2A and a heating heater 3 which is a load are connected in series. Also,
At both ends of the line of the AC power source 1, a series circuit of a reverse blocking three-terminal thyristor (hereinafter referred to as a thyristor) 4 which is a semiconductor switch means and a heating resistor 5 which is a resistor, and a bidirectional three-terminal thyristor (hereinafter, A series circuit of a triac) 6 and a heat retention heater 7 is connected to each. That is, the thyristor 4 is connected to one line of the AC power source 1.
Is connected to the other side line of the AC power source 1 and the anode of the thyristor 4, and the heating resistor 5 is connected to the one side line of the AC power source 1 separately from one side of the triac 6. The main terminal is connected, and between the other side line of the AC power supply 1 and the other main terminal of the triac 6,
The heat retention heater 7 is connected. A thermal fuse 8 for cutting off the power supply, which is blown at a predetermined fusing temperature, is inserted and connected to one side line of the AC power source 1.
The power source breaker 9 is configured by integrally molding the heating resistor 5 and the heating resistor 5. The power breaker 9 turns on the thyristor 4 when the contact 2A of the relay 2 is welded,
The heating resistor 5 is energized to generate heat, and when the heating resistor 5 reaches the fusing temperature of the thermal fuse 8, the thermal fuse 8 is fused. If necessary, a temperature fuse 10 or the like for preventing overheating of the pot body (not shown) may be separately inserted and connected between the AC power source 1 and the temperature fuse 8. Further, for products that do not require a heat retaining function, the configurations of the triac 6 and the heat retaining heater 7 may be omitted.

Reference numeral 11 is a power transformer for power conversion, and one end of a primary winding 11A of the power transformer 11 has an AC power source 1
The other end of the primary winding 11A is connected to the other side line of the AC power source 1 via the temperature fuse 8 while being connected to the other side line. A rectifier 12 composed of a diode bridge is connected to both ends of the secondary winding 11B of the power transformer 11, and a smoothing capacitor is provided to both ends of the output terminal of the rectifier 12.
13 is connected. AC voltage of AC power supply 1 is a power transformer
The voltage is reduced by 11 and this reduced AC voltage is rectified by the rectifier 12
By rectifying and smoothing by the smoothing capacitor 13 and the smoothing capacitor 13, a predetermined DC voltage is generated between the output voltage lines, and a voltage sufficient to drive the relay 2 is secured. Furthermore, as a means for stabilizing this DC voltage, a constant voltage diode 14 whose cathode is connected to the positive side output voltage line,
A current amplification transistor 15 whose emitter and collector are connected to the negative side output voltage line and whose base is connected to the anode of the constant voltage diode 14, and a current amplification transistor
15 base-collector resistors for current limiting
A constant voltage circuit 17 including 16 is provided. Constant voltage circuit 17
The stabilized DC voltage obtained in step 1 is applied as an operating voltage to the input terminals + V and -V of the control device 18 corresponding to the control means.

The controller 18 is not shown in any of the figures, but is not limited to C
It is provided with a microcomputer incorporating a PU and its peripheral circuits, and a program for executing a predetermined control sequence is stored in advance in a storage device. An input device 21 such as an operation switch and a temperature detecting device 22 such as a thermistor are connected to an input port of the control device 18, and a display device 23 such as an LED and a buzzer are provided at an output port of the control device 18. Informing devices 24 such as are connected to each. Each of these devices 21 to 24 is selectively provided as appropriate according to the specifications of the product. Further, an output terminal P for supplying a drive signal to the gate of the triac 6 via the gate resistor 25.
1 and an output terminal P2 for supplying a drive signal to the coil 2B of the relay 2 are provided in the control device 18, respectively. The control unit 18 follows the control sequence of the built-in program,
Based on the comparison between the detected temperature of the temperature detection device 22 and the set temperature, the heating heater 3 and the heat retention heater 7 are turned on and off. The controller 18, the relay 2 and the heating heater 3 constitute a heater control circuit 26 for the heating heater 3.

One end of the coil 2B of the relay 2 is connected to the negative side output voltage line and the coil 2B is connected to the negative side output voltage line.
An emitter / collector of a PNP transistor 31 provided for driving a relay is connected between the other end of B and the positive output voltage line. Further, a gate resistor 32 is provided between the base of the transistor 31 and the output terminal P2 of the control device 18.
Is provided, and the transistor 31 and the gate resistor 32 constitute a relay drive circuit 33 for driving the relay 2.

Reference numeral 41 monitors the presence / absence of a drive signal from the output terminal P2 of the controller 18 and the open / closed state of the contact 2A of the relay 2 to detect the contact welding when the contact 2A of the relay 2 is welded. It is a contact welding detection circuit that outputs a signal immediately. A gate resistor 42 is connected to the gate of the thyristor 4 from which the contact welding detection signal is output, and the gate resistor 42 and the thyristor 4 receive the contact welding detection signal from the contact welding detection circuit 41, and the power breaker 9 A power circuit breaker drive circuit 43 for activating

The contact welding detection circuit 41 determines the drive signal input X to the coil 2B of the relay 2 and the open / close signal input Y of the contact 2A as input conditions, and the determination result is used to heat the power breaker 9. Power circuit breaker drive circuit that cuts off electricity through resistor 5
It is supplied as a drive output Z to 43. Expressing this as a logic circuit, the contact welding detection circuit 41 of this embodiment is
Is configured such that the following mathematical formula is established.

[0020]

[Equation 1]

That is, when the drive signal is not output from the output terminal P2 of the controller 18, the drive signal input X is L.
However, in this case, when the contact 2B of the relay 2 is on, that is, welded, the switching signal input Y becomes H level, and therefore the power output circuit breaker drive circuit 43 contacts the drive output Z of which is L level. It is output as a welding detection signal.

In order to satisfy the logic circuit in the above mathematical expression 1, the contact welding detection circuit 41 of this embodiment has the first and second NPN type transistors 44 and 45 and the first and second resistors 46 and 47. Attention is paid to the fact that it is configured by and is provided independently of the control device 18. That is, to monitor the drive signal input X, one end of the first resistor 46 is connected to the connection point between the collector of the transistor 31 and the coil 2B of the relay 2, and the emitter of the other end of the first resistor 46 is minus. A first transistor 44 connected to the side output voltage line and having a collector connected to the base of a second transistor 45.
It is configured by connecting the bases of. Also, open / close signal input Y
Is monitored by connecting one end of the second resistor 47 to the connection point between the contact 2A of the relay 2 and the heater 3 for heating.
Of the second transistor 45 whose emitter is connected to the negative side output voltage line. The collector of the second transistor 45 is connected to one end of the gate resistor 42 so that the drive output Z of the contact welding detection signal is supplied to the power breaker drive circuit 43.

Next, the operation of the above structure will be described. When the AC power source 1 is turned on, an AC voltage is applied to the primary winding 11A of the power transformer 11 unless the temperature fuses 8 and 10 are blown. The stepped-down AC voltage output from the secondary winding of the power transformer 11 is rectified and smoothed by the rectifier 12 and the smoothing capacitor 13, and then the constant voltage circuit 1
A stable DC voltage is supplied to the input terminals + V and -V of the control device 18 by means of 7. The control device 18 controls the drive signals from the output terminals P1 and P2 so that the hot water in the container (not shown) reaches a predetermined temperature based on the comparison between the temperature detected by the temperature detection device 22 and the set temperature. By Triac 6
The main heater 2 and the contact 2A of the relay 2 are opened and closed to control the heating heater 3 and the heat-retaining heater 7 to turn on and off. That is, when a gate current is supplied to the gate of the triac 6 via the gate resistor 25 by the drive signal from the output terminal P1, the main electrodes of the triac 6 are bidirectionally connected and the heater 7 for heat retention is supplied from the AC power supply 1 to the heater 7. The AC voltage is supplied to the heat insulation heater 7 to generate heat. Also, the output terminal P2
When the transistor 31 of the relay drive circuit 33 is turned on by the drive signal from, a DC current flows into the coil 2B of the relay 2. Therefore, the contact 2A of the relay 2 is turned on,
An AC voltage from the AC power supply 1 is supplied to the heating heater 3, and the heating heater 3 generates heat.

When a drive signal is being output from the output terminal P2 of the control device 18 to the relay drive circuit 33, the drive signal input X to the coil 2B of the relay 2 becomes H level. At this time, in the contact welding detection circuit 41, the base current is supplied to the first transistor 44, and the first transistor 44 is turned on. Therefore, the base-emitter of the second transistor 45 is short-circuited, and the second transistor 45 is opened and closed regardless of whether the contact 2A is opened or closed.
Since the transistor 45 of 1 continues to be in the off state, the thyristor 4 of the power breaker driving circuit 43 is turned off and the power breaker 9 does not operate.

On the other hand, the output terminal P2 of the controller 18
When the supply of the drive signal from the relay drive circuit 33 to the relay drive circuit 33 is stopped, the drive signal input X to the coil 2B of the relay 2 becomes L level, and the first transistor 44 of the contact welding detection circuit 41
Is turned off. At this time, if the contact 2A of the relay 2 is welded and remains in the ON state, the open / close signal input Y of the contact 2A is at the H level, so the second transistor 47 is connected via the second resistor 47. The base current flows into 45, and the second transistor 45 is turned on. Therefore, the drive output Z to the circuit breaker drive circuit 43 becomes L level, and the gate current flows through the thyristor 4 via the gate resistor 42, so that the thyristor 4 turns on and the heating resistor 5
The AC voltage from the AC power supply 1 is supplied to each half wave. Then, when the temperature of the thermal fuse 8 reaches the fusing temperature due to the heat generated by the heating resistor 5, the thermal fuse 8 is blown and the energization of all circuits including the heating heater 3 is cut off.

In the normal operation in which the contact 2A of the relay 2 is not welded, the opening / closing signal input Y of the contact 2A switches from the H level to the L level when the supply of the drive signal from the output terminal P2 is stopped. Therefore, in this case, the second transistor 45 maintains the off state, and the power breaker 9
Does not work.

As described above, according to this embodiment, the control device
When the drive signal from the output terminal P2 of 18 is not output,
If the contact 2A of the relay 2 continues to be turned on, the contact welding detection circuit 41 detects this state, and immediately the drive output Z outputs the L level contact welding signal to the power circuit breaker drive circuit 43. As a result, the temperature fuse 8 for cutting off the power supply constituting the power breaker 9 can be melted and the power supply to the heating heater 3 can be quickly stopped, and the pot body due to overheating of the heating heater 7 (see FIG. (Not shown)
Can be prevented from being damaged. In addition, the contact welding detection circuit 41
Is provided separately from the control device 18 that outputs a drive signal equipped with a microcomputer. Therefore, even if the control device 18 malfunctions, the power breaker 9 does not operate correctly as in the conventional case. Nothing happens, and the welding of the contact 2A of the relay 2 can be reliably detected, and the power supply to the heating heater 3 can be promptly cut off in an emergency.

That is, a series circuit of the heater 3 for heating and the contact 2A of the relay 2 is connected between the lines of the AC power source 1,
Contact 2 of the relay 2 according to a drive signal from the controller 18
In the heater control circuit 26 for controlling the switching on and off of the heating heater 3 by turning on / off A, the presence / absence of a drive signal from the control device 18 and the open / closed state of the contact 2A of the relay 2 are monitored to determine the contact of the relay 2 Contact welding detection circuit 41 provided independently of the control device 18 which outputs a contact welding detection signal when welding 2A
A power supply circuit breaker 9 for cutting off the power supply to the heater 3 for heating from the line of the AC power supply 1; and a power circuit breaker drive circuit 43 for operating the power circuit breaker 9 by the contact welding detection signal from the contact welding detection circuit 41. Therefore, when the contact 2A of the relay 2 is welded, the power supply to the heating heater 3 can be stopped promptly and reliably.

If energization to the heating heater 3 is stopped by a breaking relay or the like, it is difficult to arbitrarily set the time until the contact of the breaking relay is opened. Since the heating resistor 5 and the thermal fuse 8 are integrally molded, if the fusing temperature of the thermal fuse 8 and the resistance value of the heating resistor 5 are arbitrarily selected in advance,
The time until the thermal fuse 8 melts can be easily changed according to each product.

That is, the temperature fuse 8 for cutting off the power supply
If the power supply circuit breaker 9 is configured by integrally molding the heating resistor 5 that melts the thermal fuse 8 by heating when the contact 2A of the relay 2 is fused, the time until the thermal fuse 8 melts can be simplified. Can be changed to

Further, since the microcomputer of the control device 18 is relatively vulnerable to electrostatic noise, etc., the control device 18
If the welding of the contact 2 is detected by the method, there is a risk of erroneous detection due to noise. However, the contact welding detection circuit 41 of the present embodiment has the first and second transistors 44 and 45 and the first and second transistors 44 and 45.
Since it is composed of discrete components including the second resistors 46 and 47, it is resistant to electrostatic noise and erroneous detection due to noise is small. In addition, one side line of the AC power supply 1 is common with the coil 2B of the relay 2, the constant voltage circuit 17, and the plus side output voltage line for applying a DC voltage to the control device 18. The number of points can be minimized, and the cost can be reduced. Further, after the thermal fuse 8 is melted, the power breaker 9 and the relay 2 which are integrated by molding can be replaced with each other, and the relay can be easily repaired.

Next, second to fifth embodiments of the present invention will be described with reference to the accompanying drawings. In each of these embodiments, the same parts as those in the first embodiment are designated by the same reference numerals, and detailed description of the common parts will be omitted.

A second embodiment of the present invention is shown in FIG. In this figure, it is noted that in this embodiment, instead of the thyristor 4 of the first embodiment, a bidirectional three-terminal thyristor, that is, a triac 51 is connected as a semiconductor switch means.
In this case, when the drive output of the contact welding detection signal becomes L level during welding of the contact 2A, the triac 51 is turned on and the AC voltage from the AC power supply 1 is supplied to the heating resistor 5 for each full wave. The amount of heat generated by the heating resistor 5 is larger than that of the configuration of the embodiment, and the thermal fuse 8 can be melted more quickly when the contacts 2 are fused. Further, it is difficult to mechanically adjust the cutoff time of the thermal fuse 8 after the power breaker 9 is molded, but at least in the structure of claim 2, the power breaker drive circuit 43 is provided with semiconductor switch means. A gate resistance 42 connected between the gate of the semiconductor switch means and the contact welding detection circuit 41,
If a series circuit of the semiconductor switch means and the heating resistor 5 is connected between the lines of the AC power supply 1, by appropriately selecting the thyristor 4 or the triac 51 as the semiconductor switch means, the heat generation amount of the heating resistor 5, and hence the power supply. The fusing time of the temperature fuse 8 for interrupting the supply can be easily changed.

Next, referring to FIG. 3, a third embodiment of the present invention will be described. In this embodiment, the normally open contact 52A and the coil 52B are used.
The power supply circuit breaker drive circuit 43 is configured by the relay 52 provided with. Specifically, the series circuit of the contact 52A of the relay 52 and the heating resistor 5 is connected between both ends of the line of the AC power source 1, and the coil 52B is connected between the positive side output voltage line and the collector of the second transistor 45. Connecting. In this case, when the drive output of the contact welding detection signal becomes L level during welding of the contact 2A, a direct current flows into the coil 52B of the relay 52, so that the contact 52A is turned on and the heating resistor 5 is supplied from the AC power source 1 to the heating resistor 5. AC voltage is supplied. Therefore, even when this coil 52A is used as the switch means of the power breaker drive circuit 43, the energization of the heating heater 3 can be promptly and reliably stopped when the contact 2A of the relay 2 is welded.

FIG. 4 shows a fourth embodiment of the present invention. In the figure, in this embodiment, a self-holding type latching relay 53 that serves as both the power breaker 9 and the power breaker drive circuit 43 is provided. This latching relay 53 is a normally closed contact 53
It has an A and a coil 53B, a normally closed contact 53A is connected to one side line of the AC power supply 1, and a coil 53B is connected between the positive side output voltage line and the collector of the second transistor 45. When the drive output of the contact welding detection signal becomes L level during welding of the contact 2A, the latching relay 53
Since a DC current flows into the coil 53B, the contact 53A is immediately switched to the OFF state, and the power supply to all circuits including the heating heater 3 is cut off. At this time, the current supply to the coil 53B is also stopped, but the latching relay 53 has the contact 53A.
Since the above state is maintained as it is, the AC voltage is not supplied to the heating heater 3 thereafter. Thus, in the structure of claim 1, the power breaker 9 and the power breaker drive circuit 43 are constituted by the latching relay 53 in which the normally closed contact 53A is inserted and connected to one side line of the AC power supply 1. Also, when the contact 2A of the relay 2 is welded, the energization of the heating heater 3 can be promptly and surely stopped. Moreover, in this case, each function of the power breaker 9 and the power breaker drive circuit 43 can be realized by one component, and the number of components can be significantly reduced.

FIG. 5 shows a fifth embodiment of the present invention. In this embodiment and the first embodiment, a common load voltage supply line is connected between one side line of the AC power supply 1 and each end of the heating heater 3, the heat retaining heater 7 and the heating resistor 5, A point where a thermal fuse 8 for cutting off the power supply is inserted and connected to the load voltage supply line, and a contact welding detection signal line from the collector of the second transistor 45 to the gate resistance 42 of the power breaker driving circuit 43, plus The configuration is different in that a series circuit of a resistor 54 and a display LED 55 as a contact welding notification means is connected to the side output voltage line, but the configurations of the other parts are the same.

In this case, when the contact 2A of the relay 2 is welded and the drive output of the contact welding detection signal becomes L level,
A direct current flows into the LED 55 through the resistor 54, and this L
When the ED55 is turned on, the thyristor 4 is turned on, the heating resistor 5 generates heat, and the thermal fuse 8 is blown.
In this case, the power supply from the AC power supply 1 to the heating heater 3 and the heat retention heater 7 is cut off, but the power transformer 11
Since the AC voltage is continuously supplied to, the respective functions of the control device 18 and the lighting state of the LED 55 are maintained as they are.

As described above, if the temperature fuse 8 of the power circuit breaker 9 is inserted and connected to at least the load voltage supply line from the heater 3 for heating to one side line of the AC power source 1, the pot body may be damaged, It is possible to cut off only the power supply to the heater 3 for heating which is in danger of ignition and to continue other functions such as the control device 18. Further, if the LED 55 that operates according to the contact welding detection signal from the contact welding detection circuit 41 is further provided, it is possible to quickly understand that the operation is stopped due to the welding of the contact 2A, and quick repair is possible. It is possible to achieve In addition, as means for notifying the welding of the contact 2A,
The notification means such as a buzzer may be used instead of the display means such as the LED 55.

The present invention is not limited to the above embodiment, and various modifications can be made within the scope of the gist of the present invention. For example, in each of the above embodiments, the contact welding detection signal from the contact welding detection circuit 41 is sent to the controller 18
When the contact welding detection circuit 41 detects the welding of the contact 2A, a pulse drive signal is output from the output terminal P2 of the control device 18.
It is possible to separate A and aim for a life-prolonging effect. The logical relationship between the input and output of the contact welding detection circuit 41 depends on the circuit configuration of the power breaker 9 and its surroundings.
You may change it suitably.

[0040]

According to the contact welding protection device of the first aspect,
In a heater control circuit for connecting a series circuit of a heating heater and a contact of a relay between power supply lines, and opening and closing the contact of the relay in response to a drive signal from a control means to control the on / off of the heating heater, A contact welding detection circuit provided independently of the control means for monitoring the presence or absence of a drive signal from the control means and the open / closed state of the contact of the relay and outputting a contact welding detection signal when the contact of the relay is welded. A power supply circuit breaker that cuts off power supply from the power supply line to the heating heater; and a power circuit breaker drive circuit that operates the power circuit breaker according to a contact welding detection signal from the contact welding detection circuit. Therefore, when the contact of the relay is welded, the energization of the heating heater can be stopped promptly and reliably.

The contact welding protection device according to a second aspect of the present invention is, in the structure of the first aspect, a thermal fuse for cutting off the power supply and a resistor for fusing the thermal fuse by heating when the contacts of the relay are fused. Since the power breaker is configured by integrally molding and, the time until the thermal fuse is blown can be easily changed.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram showing a first embodiment of the present invention.

FIG. 2 is a circuit configuration diagram showing a second embodiment of the present invention.

FIG. 3 is a circuit configuration diagram showing a third embodiment of the present invention.

FIG. 4 is a circuit configuration diagram showing a fourth embodiment of the present invention.

FIG. 5 is a circuit configuration diagram showing a fifth embodiment of the present invention.

[Explanation of symbols]

 1 AC power supply (power supply) 2 Relay 2A contact 3 Heating heater 5 Heating resistance (resistor) 8 Temperature fuse 9 Power breaker 18 Control device (control means) 26 Heater control circuit 41 Contact welding detection circuit 43 Power breaker drive circuit

Claims (2)

[Claims] 1. A heater which connects a series circuit of a heating heater and a contact of a relay between power supply lines, and opens and closes the contact of the relay in response to a drive signal from a control means to control the on / off of the heating heater. The control circuit is provided independently of the control unit that monitors the presence or absence of a drive signal from the control unit and the open / closed state of the contact of the relay, and outputs a contact welding detection signal when the contact of the relay is welded. A contact welding detection circuit, a power breaker that shuts off the power supply from the power supply line to the heating heater, and a power breaker drive that activates the power breaker by a contact welding detection signal from the contact welding detection circuit A contact welding protection device for a heater control circuit, which is provided with a circuit. 2. The power circuit breaker is configured by integrally molding a temperature fuse for cutting off the power supply and a resistor for melting the temperature fuse by heating when the contacts of the relay are welded. The contact welding protection device for the heater control circuit according to claim 1.