JPS6028116B2 - electric heater - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is an electric heater for controlling the temperature of a heater, which is a load, and for preventing localized temperature rises. This invention relates to an electric heater equipped with a device for preventing relay wear.

Conventionally, there has been a device of this type as shown in FIG.

That is, in FIG. 1, 1 is an AC power source, 2 is a planar heater as a load, and 3a is a relay point.The AC power source 1, heater 2, and relay contact 3a form a series circuit.
3b is a relay coil, 4 is a resistor connected in parallel with the relay coil 3b, 5 is a triac, and 6 is a gate resistor of the triac 5. Also, A indicated by a broken line
The part is the IJ circuit of the triac 5. In the trigger circuit A, 7 is a first thyristor connected to one end of the gate resistor 6 and one end lb of the AC power supply 1, 8 is a capacitor, and 9, 10, 11 are resistors; , 10, 11 is the AC power supply 1
The gate of the first thyristor 7 is connected to the connection point of the resistors 10 and 11. 12 is the resistor 9
and 10 and a constant voltage diode connected between the cathode of the first thyristor 7; 13 is the constant voltage diode 1;
A heat-sensitive thyristor connected in parallel with heater 2 and thermally coupled to heater 2.

In addition, a plurality of heat-sensitive thyristors 13 may be connected in parallel as necessary when it is necessary to prevent local excessive temperature rise. 14 is a variable resistor for setting switch temperature connected between the gate and anode of the heat-sensitive thyristor 13, and 15 is a capacitor connected in parallel to the variable resistor 14 for noise prevention.

16 is a capacitor, 17 is a resistor, and 18 is a second thyristor. A series circuit of the capacitor 16, resistor 17, and second thyristor 18 connects the anode of the first thyristor 7 and the other end la of the AC power supply 1. connected between.

19 is a diode connected in antiparallel to the second thyristor 18; 20 is a diode connected between the gate and cathode of the second thyristor 18; 21 is a diode connected between the gate of the second thyristor 18 and the AC power supply 1; A trigger resistor 22 connected between one end lb of the trigger resistor 22 is a speed-up capacitor connected in parallel with the resistor 21.

Next, the operation will be explained.

First, when the temperature of heater 2 is low, thermal thyristor 1
3 is in the off state, so when the terminal la of the AC power supply 1 is positive, the first thyristor 7 is connected to the capacitor 8 and the resistor 9.
, 10 triggers on the volts of the power supply. Therefore, a gate current flows through the triac 5 through the resistor 4, the relay coil 3b, the triac 5, the gate resistor 6, and the first thyristor 7, so that the triac 5 is turned on. At this time, the capacitor 6 is charged through the diode 19 and the resistor 17. Next, when one end lb of the AC power supply 1 becomes positive, the second thyristor 18 is triggered at approximately the same voltage via the resistor 21 and the capacitor 22, and the triac 5 is triggered by the discharge current of the capacitor 16. That is, when the heat-sensitive thyristor 13 is off, the triax 5 is turned on and excites the relay coil 3b. Therefore, the relay contact 3a is closed and the load heater 2 is heated. When the temperature rises due to heating of the heater 2 and the heat-sensitive thyristor 13 turns on, the gate current of the first thyristor 7 increases
3, the triac 5 as well as the first thyristor 7 are turned off.

Therefore, since the capacitor 6 is not charged, even if a reverse voltage is applied, the triac 5 is turned off and the relay coil 3b is not excited. Therefore, power is no longer supplied to the heater 2 of the load. In this way, temperature control or overheating prevention becomes possible. The reason why the relay coil 3b is used in this circuit is to prevent the temperature of the triac 5 from rising by not allowing the load current to flow directly to the triac 5 since the load capacity becomes very large.

The conventional circuit operates as described above, so even though the triac 5 switches at zero volts, due to the delay of the relay coil 3b, the load heater 2 does not switch to zero volts and turns on at a point other than zero volts.・You will be repeatedly turned off.

In addition, when the relay switches at a voltage other than zero volts of alternating current, there is a drawback that the contacts are considerably worn out due to arcing and the like. This invention was made to eliminate the above-mentioned drawbacks. A second triax is connected in parallel to the relay contact, and this triax is turned on only for the delay time of the relay, thereby controlling the load heater at zero volts. The purpose is to

This invention will be explained below. FIG. 2 is a circuit diagram showing an embodiment of the present invention.

In FIG. 2, 1 to 6 and A are the same as in FIG. 1, and only resistors 9 to 11 of A are shown. 3
A second triac connected in parallel with the relay contact 3a, 31 its gate resistor, 32 a diode, 33 a timer power transformer, 34 a delay timer circuit, and 35 the delay timer circuit 34. A photocoupler for a signal source for starting, which connects the light emitting element 35A and the light receiving element 3.
It consists of 58.

It is assumed that the output of the delay timer circuit 34 is obtained at a pulse or DC level. Further, 36 is a resistor for limiting the current of the light emitting element 35A. 37 is a diode,
38 is a capacitor, which constitutes a smoothing circuit 39. 40 is a diode.

Next, the operation of the circuit shown in FIG. 2 will be explained in detail together with the operation sequence shown in FIG.

When the thermal thermostatic IJ star 13 in the trigger circuit A is switched from on to off, it triggers the triax 5 with zero volts. At the same time, the second triac 30 connected to the trigger circuit A via the gate resistor 31 is also triggered at zero volts to supply power to the heater 2 as the load.
Also, since the first triac 5 is on, the third triac
As shown in the figure, there is a delay of the relay delay time (approximately 5 to 1 seconds), and the relay contact 3a is turned on. Therefore, the second
The triac 30 is turned off. The load current therefore flows through the second triac 30 for a time t and then commutates to the relay contact 3a. Next, when the heat-sensitive thyristor 13 is turned on, the first triac 5 is turned off.

At this time, the light-emitting element 35A detects that the heat-sensitive thyristor 13 is on, and this is transmitted to the light-receiving element 35B, and the delay timer circuit 34 is started, and the second
A gate current is supplied to the triax 30 through the gate resistor 31. Therefore, the second triac 30
At the same time as the triac 5 turns off, it remains on for a time t2. During this time, the relay coil 3b is de-energized and the relay contact 3a is turned off. As described in detail above, the present invention has the following advantages because the second try-hook is connected and controlled in parallel with the contact for turning on and off the heater.

■ No radio noise is generated because the heater, which is the load, is controlled entirely by a zero-volt switch.

■ Also, since there is no arcing in the relay contacts, the life of the relay will be longer and there will be fewer failures.

■ Since the second triac is operated for the delay time of the relay, the capacity of the second triac can be small.

In addition, the first triac can also be a low-power triac, making it inexpensive. ■ Since the heat generated by the triax is small, there is almost no need for heat dissipation fins.

Therefore, the circuit can be made smaller. Brief Description of the Drawings Figure 1 is a circuit diagram showing the temperature control circuit of a conventional electric heater.
FIG. 2 is a circuit configuration diagram of a temperature control circuit for an electric heater showing an embodiment of the present invention, and FIG. 3 is a diagram showing the operation sequence of FIG. 2.

In the figure, 1 is an AC power supply, 2 is a heater, 3a is a relay contact,
3b is a relay coil, 4 is a resistor, 5 is a try hook,
6 is a gate resistor, 7 is a first thyristor, 8 is a capacitor, 9, 10, 11 are resistors, 12 is a constant voltage diode, 13 is a heat sensitive thyristor, 14 is a variable resistor, 15,
16 is a capacitor, 17 is a resistor, 18 is a second thyristor, 19, 2-way diode, 21 is a resistor, 22 is a capacitor, 30 is a triac, 31 is a gate resistor, 32 is a diode, 33 is a power transformer , 34 is a delay timer circuit, 35 is a photocoupler, 35A is a light emitting element, 3
5B is a light receiving element. Note that the same reference numerals in the figures indicate the same or corresponding parts. Figure 3 Figure 1 Figure 2

Claims (1)

[Claims] 1. A series circuit consisting of an AC power source, a relay coil, and a first triax, a series circuit consisting of a heater connected to the AC power source, and a relay contact operated by excitation of the relay coil, connected in parallel to the relay connection. a second triax, a trigger circuit for operating the first and second triaxes with a zero-volt switch depending on the temperature of the heater; a thermosensitive trigger circuit for operating the first and second triaxes according to the temperature of the heater and turning off the first triax; 1. An electric heater comprising: a heat-sensitive element; and a delay timer circuit that starts following the operation of the heat-sensitive element and triggers only the second tri-attack for a predetermined period of time.