JPS6040738B2 - switching circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a switching circuit that disconnects an electric path without contact using a semiconductor switching element (hereinafter referred to as a three-terminal thyristor) such as an SCR or a triac due to arc resistance.

This kind of 3-terminal thyristor is used to break the electric circuit by placing contacts with different operating times before and after the thyristor, and triggering the thyristor at the first operating point, followed by a slight delay. The next contact is turned on, and vice versa when it is turned off, considering arc resistance performance.

The current change rate is lowered to reduce noise. A conventional example of this is shown in FIG.

To explain this, reference numeral 1 denotes an input side terminal to which a relay 2 which operates according to a signal is connected. This relay 2 has three contacts 2a, 2b, and 2c that operate at different times. 3 is an AC power supply, 4 is an inductive load, and 5 is a three-terminal thyristor, the terminals T1 and TO are connected to the power supply 3 and load 4 via an output terminal 6.

The upper stage contact 2a, which operates in the first stage of the relay 2, is connected to the gate terminal G of this three-terminal thyristor 5,
When this cross point 2a turns on, the gate terminal G is triggered,
A voltage is applied to both terminals T1 and TO', and the thyristor 5 is turned on. This on state is maintained until the current drops below a certain level. 7 is a zero cross, which is connected to the upper contact 2a and turns on and off when the current waveform approaches zero.

The middle contact 2b is connected in parallel with the resistor 8 so that the middle contact 2b is turned on with a delay time longer than the second half cycle when the upper contact 2a is turned on. This resistor 8 is used for normal triggering of the thyristor 5, for the opening/closing arc of the contact 2b, and for the flow after the thyristor 5 is turned on. Further, the second stage contact 2c that turns on at the final stage is the thyristor 5.
It is paralleled with. When turning off, contacts 2a, 2b,
2c is the reverse operation order. Next, the operation of the switching circuit of the present invention will be explained with reference to FIG. 2. When an input signal is input to the input terminal 1, the IJ relay 2 operates.

This operation of relay 2 causes upper contact 2a to close. Then, the zero cross 6 triggers the IJ star 5 from near zero, as shown in FIG. 2, and the current flows. The middle contact 2b turns on more than half a cycle after the upper contact 2a,
Power supply 3 - load 4 regardless of zero cross 6 of upper contact 2a
- Resistor 8 - Middle contact 2b - Gate terminal G and thyristor 5
is always energized. The final post-stage contact 2c is turned on with a further delay. Therefore, the inrush current does not occur at the subsequent contact 2c. Therefore, the circuit of power source 3 - load 4 - one point 2c of the latter stage is activated, and the load is operated. When the load 4 is subsequently cut off, the relay 2 returns to normal operation as the input signal disappears, and the subsequent contact 2c is first turned off.

In this case, the arc does not fly due to the parallel circuit of the thyristor 5. Thereafter, the middle contact 2b is turned off and the relationship between the contact 2b and the thyristor 5 is released, but the thyristor 5 is still under trigger restraint due to the zero cross 6 and the upper contact 2a. After that, the near-zero operation of this zero cross 6 turns off, and the thyristor 5 also turns off, cutting off the load 4. In addition, Fig. 2 shows the power supply, input signal, each contact 2a, 2b, 2c,
The operation time of zero cross 6 is shown. This middle stage contact 2b prevents the circuit from being directly disconnected at the contact 2c due to the timing of operation of the point adjacent to the zero cross 6 and the second stage contact 2c overlapping. In this way, the rate of change in current can be lowered and noise can be reduced; however, since at least three contacts with time differences are required, it is difficult to adjust the relay contacts.

Additionally, there was a possibility that malfunctions would occur. Therefore, an object of the present invention is to provide a novel switching circuit that eliminates such conventional drawbacks. Hereinafter, one embodiment of the present invention will be described with reference to FIG. 3 and subsequent figures, but the same parts in the slave circuit of FIG.

A light emitting diode 9 is connected in series with the relay 2.

10' is a zero cross trigger circuit that operates in response to the light irradiated by the light emitting diode 9; 11 is a light emitting diode 9;
This diode is connected in parallel with the relay 2 and is used to protect the light emitting diode 9.

2x is a front-stage contact, which operates with a delay of more than half a cycle from the start of excitation to relay 2.

2y is a rear contact, which closes slightly later than the front contact 2x and opens earlier.

Next, the operation of the configuration of the present invention will be explained with reference to FIG. 4. When an input signal is input to the input terminal 1, the light emitting diode 9 emits light, the zero cross trigger circuit 10 responds, and a trigger pulse is generated when the load current is near zero. ip is generated and the thyristor 5 is triggered and turned on.

At the same time, the relay 2 is also energized, but the front contact 2x turns on a little later than when the IJ is triggered, and thereafter triggers the siris 5. After a further delay, the latter contact 2y turns on. Therefore, the arc of inrush current is not generated at the subsequent contact 2y, and the power supply 3-
A closed circuit is formed between the load 4 and the contact 2y, and the load is operated. Thereafter, when the load 4 is cut off, the input signal disappears.

This is because the light emitting diode 9 does not emit light and the relay 2 is not excited, so the rear contact 2y is turned off first, and then the front contact 2x is turned off.
turns off. Therefore, no arc is generated at these contacts 2x and 2y, and after the contacts 2x and 2y are turned off, the thyristor 5 is turned off when the load current is near zero, cutting off the load. Note that if an input signal is accidentally released to input terminal 1 in the opposite direction, diode 11
Damage to the light emitting diode 9 due to short circuit can be prevented.

That is, according to the present invention described above, when the load current is turned on and off near zero, only two relay contacts are required.

The zero-cross trigger circuit that turns on the thyristor first is optically coupled, so it does not require any contacts and there is no delay in response, and it can be activated prior to the operation of the contacts without using any delay means between the relay and the contacts. It is possible to provide a switching circuit that can operate smoothly, is easily adjustable overall, and has reliable operation.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram of a conventional switching circuit, Fig. 2 is a waveform diagram showing its operation, Fig. 3 is a circuit diagram showing an embodiment of the present invention, and Fig. 4 is a waveform diagram showing its operation. . 1...Input terminal, 2...Relay, 3.
...AC power supply, 4...Load, 5...
Thyristor, 9... Light emitting diode, 10...
...Zero cross trigger circuit, 2x... front stage contact, 2y... rear stage contact. So'IQ na 21 phantom talent 21 phantom spear 4 sen

Claims (1)

[Claims] 1. a 3-terminal thyristor, a load connected in series with the 3-terminal thyristor to an AC power supply, and a front-stage contact of a relay connected to the gate terminal of the 3-terminal thyristor that turns on with a delay of more than half a cycle from an input signal; a zero cross trigger circuit optically coupled to the input side that turns on the three-terminal thyristor near zero prior to the operation of the front contact of the relay; A switching circuit comprising a rear contact of the relay connected in parallel to the three-terminal thyristor, which turns off before a front contact of the relay when turned off.