JPH0389425A - Relay control circuit - Google Patents

Abstract

PURPOSE:To release a deposited contact by providing a contact deposition detecting circuit detecting the deposition of a relay contact and a pulse generating circuit generating a pulse signal in response to the detection of contact deposition and applying the pulse signal to the relay contact. CONSTITUTION:When the contact 2a of a relay 2 is lightly deposited, the current flowing in a heater 1 can not be cut off, and the heater 1 becomes a high temperature. This high temperature is detected, a temperature adjusting circuit 15 turns off a transistor Tr1 to cut off the relay 2. The contact 2a is deposited and not returned, thus the heater 1 can not be stopped, a current is continuously induced in a current transformer 16, and the voltage is outputted. When the induced voltage is continued for a preset period or longer, the output of a comparing circuit 21 repeats 'H' and 'L' actions, and a pulse signal is outputted from the circuit 21. A transistor Tr2 is turned on and off in pulses by the pulse signal of the circuit 21, and the pulse voltage is applied to the relay 2. The deposition of the contact 2a of the relay 2 is released.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to a relay control circuit used, for example, to control a heater of an electronic carpet.

(B) Conventional technology Conventionally, as shown in FIG. 4, heater control for electronic carpets involves connecting a contact point 2a of an electromagnetic relay 2 to a heater 1 in series, supplying power from an AC power source 3, and The AC voltage from the AC power source 3 is rectified, smoothed, and made into a constant voltage by the constant voltage circuit 4, and then applied to the relay drive circuit 5, and the relay drive circuit 5 flows to the electromagnetic relay 2 in response to the output of a temperature control circuit (not shown). It turns on/off the current and opens and closes the relay contact 2a.

(c) Problems to be solved by the invention In the conventional example described above, the heater (load) is
is under control. Therefore, when contact welding occurs at the end of the electromagnetic relay's lifespan, even when the circuit should be turned off,
The relay contacts do not open and current continues to flow through the heater, promoting contact welding and increasing the heater temperature.
For example, there was a problem in that the entire electronic carpet, which is an applicable product, was damaged.

The present invention has been made in view of the above-mentioned problems, and it is an object of the present invention to provide a relay control circuit that can detect welding of contacts and remove the welded contacts when they occur.

(d) Means and Effects for Solving the Problems The relay control circuit of the present invention opens and closes the relay contacts by connecting a relay contact to a load and turning the relay on and off by a relay drive circuit, thereby providing a connection to the load. A contact welding detection circuit that detects welding of the relay contacts, and a pulse generation circuit that generates a pulse signal in response to the contact welding detection and applies the pulse signal to the relay contacts. It is equipped with

In this relay control circuit, if light welding occurs on the relay contacts, the contact welding detection circuit detects this, and accordingly the pulse generation circuit generates a pulse signal and applies it to the relay contacts. This releases the welding of the relay contacts.

(E) Examples The present invention will be explained in more detail with reference to Examples below.

FIG. 1 is a schematic block diagram of a heater control circuit for an electronic carpet showing one embodiment of the present invention.

This heater control circuit is the same as the conventional example shown in FIG. 4 in that it includes a heater 1, a relay 2 and its contacts 2a, an AC power source 3, a constant voltage circuit 4, and a relay drive circuit 5. The feature of this embodiment is that it is provided with a contact welding detection circuit 6 and a pulse generation circuit 7 which generates a pulse signal and applies it to the relay drive circuit 5 in response to the detection of welding by the contact welding detection circuit 6.

A more specific circuit connection diagram of the heater control circuit shown in FIG. 1 is shown in FIG. In the figure, terminals P,
, Pz are connected to an AC power source.

The constant voltage circuit 4 includes a transformer 11 that converts AC voltage into voltage.
, a bridge type rectifier circuit 12 that rectifies the converted AC voltage, a smoothing capacitor 13, and a Zener diode 14. A power supply voltage is supplied from this constant voltage circuit 4 to a relay drive circuit 5, a contact welding detection circuit 6, and a pulse generation circuit 7.

The relay drive circuit 5 includes a temperature control circuit 15 and a drive transistor Tr.
The collector of + is connected to one end of relay 2 via diode D2. The other end of this relay 2 is connected to the output end of a constant voltage circuit 4.

The contact welding detection circuit 6 includes a current transformer 16 that detects the current flowing through the heater 1, a bridge type rectifier circuit 17 that rectifies the signal derived from the current transformer 16, and resistors R6, R1,
Smoothing circuit 18 consisting of diode D3 and capacitor C3
, a reference voltage circuit 19 consisting of resistors Rs, R4, and a capacitor C2, and a comparator circuit 20 which receives the voltage from the smoothing circuit 18 at one input terminal and receives the reference voltage from the reference voltage circuit 19 at one input terminal. has been done. The output of the comparison circuit 20 is connected to the driving transistor T via the diode D1.
r, is connected to the collector of

In the pulse generation circuit 7, the voltage across the Zener diode 14, that is, the voltage obtained by dividing the power supply voltage by the resistors Rs and Rh, is applied to the input terminal of the comparison circuit 21.
A resistor R7 is connected between the input terminal and the output terminal of the comparator circuit 21, and a Zener diode D is connected between the output terminal and the input terminal of the comparator circuit 21.
4 and a resistor R, and a series circuit of a diode D5 and a resistor R9 are connected in parallel. In addition, diode D4
and are connected with opposite polarity. Further, a capacitor C3 is connected between one input terminal of the comparator circuit 21 and the ground GND. Further, the output terminal of the comparison circuit 21 is connected to the output terminal of the comparison circuit 20. The series circuit of resistors R1°, Ro, R, t is connected to the constant voltage circuit 4, and the resistors R1° and Ro
is connected to the output terminal of the comparator circuit 21, and the resistor R0
The connection point between and Rlg is connected to the base of the transistor Tr.

The collector of the transistor Trt is connected to the anode side of the diode D2, and the emitter is connected to ground J'GND. Moreover, the transistor Tr.

A capacitor c4 is connected between the base of and ground GND.

Next, the operation of the embodiment heater control circuit configured as described above will be explained.

Relay contact 2a is closed, and when current flows through heater 1, the temperature rises; conversely, relay contact 2a opens, and heater 2
If no current flows through the heater, the temperature of the heater will drop. This heater temperature is detected by a sensor (not shown) of the temperature control circuit 15, and the output of the temperature control circuit 15 is turned on/off based on this temperature. In response to this, the driving transistor Tr is also turned on/off, turning on/off the contact 2a of the relay 2, and controlling the temperature of the heater I.

Here, if the contacts 2a of the relay 2 are lightly welded, the heater 1
The current flowing through the heater 1 cannot be turned off, and the heater 1 becomes hot. Since this high temperature is detected, the temperature control circuit 15 turns off the transistor Tr in order to turn off the relay 2. Therefore, the cathode side of diode D is H'' (high)
becomes. However, despite the temperature control off signal, contact 2a of relay 2 has welded and has not returned, so heater 1
cannot be stopped (turned off). For this reason, the current transformer 16 has
Current is continuously induced and voltage is output. This induced voltage is rectified by the rectifier circuit 17 and charged in the capacitor C1 of the smoothing circuit 18. However, if the induced voltage continues for a predetermined time or more, the voltage of the capacitor C1 becomes higher than the reference voltage, and the comparator circuit 20 The output of the diode D becomes "H11. Therefore, the cathode of the diode D and the comparator circuit 20
The outputs of the comparator circuit 21 become "H", and the output of the comparator circuit 21, which was 11 L" (low) due to being absorbed by these outputs, becomes "H".
l Hl''. Charging of the resistor R1 and capacitor C1 is started at this HII, and when the voltage of the capacitor C3 becomes higher than the reference voltage from the resistors Rs and Rh, the comparator circuit 2
The output of 1 becomes “L II”, and this time the capacitor C,
, R, starts discharging and the voltage of the capacitor C1 becomes below the reference voltage, the output of the comparator circuit 21 becomes 'H' again, and thereafter the operation of 'H' and 'L' is repeated, and the pulse signal is output to the comparator circuit. 21. The pulse signal output from the comparator circuit 21 turns the transistor Tr on and off in a pulse manner, and applies a pulse voltage to the relay 2.

This releases the welding of the contacts 2a of the relay 2. When the contact welding of the relay 2 is released, the heater current will no longer flow, and therefore no signal will be derived from the current transformer 16.
The output of the comparator circuit 20 becomes "L 11", and the comparator circuit 21
Since the output is forced to "'L", the pulse signal also stops and the original temperature control operation returns.

FIG. 3 is a circuit diagram showing a heater control circuit according to another embodiment of the present invention. The example heater control circuit shown in FIG. 2 shows the case where contact welding is detected using a current transformer.
The feature here is that a photocoupler is used to detect contact welding. Therefore, in FIG. 3, the constant voltage circuit 4
The specific circuit of the relay drive circuit 5 is the same as that shown in FIG.

In the heater control circuit of this embodiment, a series circuit of a diode D6, a resistor R0, and a light emitting diode LD of a photocoupler 22 is connected in parallel to the heater 1.

The contact welding detection circuit 6 includes an input circuit 23 consisting of a phototransistor PT of a photocoupler 22, resistors R, , R2, and a capacitor C1, a reference voltage circuit 19, and a comparison circuit 20.

The pulse generating circuit 7 is different in that only a resistor R8 is connected between the output terminal and one input terminal of the comparator circuit 21, but the other connections u/ are the same as those in FIG.

The basic heater temperature control operation by turning on/off the relay 2 by the temperature control circuit 15 in this embodiment circuit is the same as that in FIG.

If the contacts 2a of the relay 2 are lightly welded, the current flowing to the heater 1 cannot be turned off, and the heater 1 becomes hot. Since this high temperature is detected, the temperature control circuit 15 turns off the relay 2 by turning off the transistor Tr.

turn off. Therefore, the cathode side of the diode D1 becomes "H11". However, despite the temperature control off signal, the contact 2a of the relay 2 is welded and has not returned, so the heater 1 cannot be stopped and the photocoupler 22 emits light. Current continues to flow through the diode LD.Therefore,
Light continues to enter the phototransistor PT of the photocoupler 22, and eventually the charging voltage of the capacitor C3 becomes higher than the reference voltage, and the output of the comparator circuit 20 becomes H". Therefore, the cathode of the diode D1 and the output of the comparator circuit 2o Tomo°“
HII, and the output of the comparator circuit 21, which was "L" (low) due to being sucked into these outputs, becomes "H".
Charging of resistor R1B and capacitors C and l starts at "H", and when the voltage of capacitor C3 becomes higher than the reference voltage from resistors R, R, the output of comparator circuit 21 becomes "L'°, and next time When the capacitor C3 and the resistor R8 start discharging, and the voltage of the capacitor C8 becomes lower than the reference voltage, the output of the comparator circuit 21 becomes "H" again, and thereafter "H" and "
The operation of "L" is repeated, and a pulse signal is output from the comparator circuit 21. The transistor Tr is turned on/off in a pulse manner by the pulse signal output of the comparator circuit 21, and a pulse voltage is applied to the relay 2. The welding of the contacts 2a of the relay 2 is released.The welding of the contacts of the relay 2 is released, the heater current stops flowing, and the photocoupler 2
No current flows through the light emitting diode LD of 2, and the comparator circuit 20
Since the output of the comparator circuit 21 becomes "L" and the output of the comparator circuit 21 is forced to "L", the pulse signal also stops and the original temperature control operation returns.

Although the above embodiment has been described with respect to a heater control circuit for an electronic carpet, the present invention is not limited thereto and can be applied to various relay control circuits.

(F) Effects of the Invention According to the present invention, a contact welding detection circuit for detecting welding of relay contacts and a pulse generation circuit are provided, and upon detection of welding, a pulse signal is generated from the pulse generation circuit and applied to the relay, Since it releases the welded contacts, even if light welding occurs, it can be removed immediately and it will not cause any serious damage, so it can prevent damage to the entire device that incorporates this relay control circuit, such as an electronic carpet, and can be used for a long time. It has the advantage of increasing its lifespan and reducing complaints from the market.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a heater control circuit showing one embodiment of the present invention, FIG. 2 is a diagram showing a specific circuit example of the same heater control circuit, and FIG. 3 is a block diagram of a heater control circuit according to another embodiment of the present invention. FIG. 4 is a circuit diagram showing a specific circuit example of the control circuit. FIG. 4 is a block diagram showing a conventional heater control circuit. l: Heater, 2: Relay 2a: Relay contact, 5: Relay drive circuit, : Contact welding detection circuit, : Pulse generation circuit.

Claims (1)

[Claims] (1) In a relay control circuit that connects a relay contact to a load and turns the relay on and off by a relay drive circuit to open and close the relay contact and control power supply to the load, welding of the relay contact is prevented. A contact welding detection circuit to detect,
A relay control circuit comprising: a pulse generation circuit that generates a pulse signal in response to the contact welding detection and applies the pulse signal to the relay contact.