JPH03219313A - Load switching circuit for ac power - Google Patents

Abstract

PURPOSE:To alternately turn on and off power supply to two loads connected to an AD power source by using a tripod transformer and a photocoupler, and turning on/off the voltage of secondary coil of the tripod transformer completely insulated from an AC power source and held at a stable and low voltage by means of an operation switch. CONSTITUTION:The external operation switch 9 is connected to the secondary coil 7 of the tripod transformer 1. A smoothing electrolytic capacitor C4 and the light emitting element LD of the photocoupler PC are connected to the DC output terminal of a rectifier bridge circuit 14 in parallel. The light receiving element PT of the photocoupler PC is connected between the base and emitter of a transistor (TR) Q1 and the emitter/collector of the TR Q1 is connected between the DC output terminal of a rectifier bridge circuit 13. The AC input terminal of the circuit 13 is connected to a bidirectional three-terminal thyristor TRC1, which is connected to a normally turned on load 11 in series and then connected to the AC power source 10. Consequently, power supply to two load, i.e. the normally turned on load 11 and a normally turned off load 12, connected to the AC power source can be switched.

Description

Detailed Description of the Invention (a) Industrial Application Field This invention uses a tripod transformer to turn on and off a safe, low-voltage secondary coil voltage that is reliably insulated from the AC power source using an external operation switch. The present invention relates to an AC power load switching circuit that switches power supply to a load that is always on and a load that is always off connected to a power source.

(B) Conventional technology Most of the control circuit units for AC power using conventional thyristors, bidirectional three-terminal thyristors, etc. (J-Solirad state relays, abbreviated as 5SR) are always 0FF (make circuit type). Of course, there are no electromagnetic relays or electromagnetic contactors that use the AB contact method (meter break circuit method).

(c) Problems to be Solved by the Invention As mentioned above, in an AC power control circuit unit using a bidirectional three-terminal thyristor, there is no AB contact system, so an AB contact or a B contact is required. In circuits, adding contact points, expensive, and large electromagnetic relays to the output of SSRs, which are small, lightweight, semi-permanent, and have a long lifespan, has the disadvantage of halving the value of non-contact points and increasing space. Ta.

This invention was made with attention to the above-mentioned problems, and the output of a low-voltage secondary coil that is completely insulated from the AC power supply and is safe is opened and closed by a switch, so that the output is always ON and connected to the AC power supply. It is an object of the present invention to provide a load switching circuit that can switch power supply to two loads that are always OFF.

(d) Means and operation for solving the problems The AC power load switching circuit of the present invention has a gap in one of the outer legs of the tripod core, a primary coil in the other outer leg, and a primary coil in the center leg. 2
a tripod transformer formed by winding a tertiary coil around an outer leg having the gap, the primary coil being connected to an alternating current power supply; and an operation switch having one end connected to the secondary coil of the tripod transformer; A rectifying bridge circuit whose AC input terminal is connected in series to the secondary coil and the operation switch, a photocoupler having a light emitting element connected to the DC output terminal of this rectifying bridge circuit, and a light receiving element of this photocoupler having a base. A transistor connected between the emitters, a second rectifier bridge circuit that connects the collector and emitter of this transistor to a DC output terminal, and an AC input terminal of this second rectifier bridge circuit connected to the second rectifier bridge circuit through a resistor. A first bidirectional three-terminal thyristor is connected between two electrodes and a gate, and connects a load that needs to be turned on in series to an AC power source; a pair of diode circuits, and a series circuit of this diode circuit and a tertiary coil are connected between the gate and the first electrode, and a second bidirectional three-terminal thyristor connects a load that needs to be turned off at all times to an AC power source in series. It consists of

In this AC power load switching circuit, the operation switch is OFF.
In state F, no AC input is made from the secondary coil of the tripod transformer to the first rectifying bridge circuit, so no DC output voltage is derived, and the light emitting element of the photocoupler does not light up. Accordingly, the light receiving element also has a high resistance due to this,
The transistor is turned on, and the output of the second rectifier bridge circuit is short-circuited. Therefore, the AC signal input to the second rectifier bridge circuit is directly transmitted to the first rectifier bridge circuit.
is applied to the gate of a bidirectional three-terminal thyristor, and the ON
do. This supplies AC power to the first load.

On the other hand, when the operation switch is OFF, no voltage is induced in the tertiary coil, so the second bidirectional three-terminal thyristor is not turned on, and the second load is not supplied with AC power.

On the other hand, when the operation switch is turned on, AC input is given to the first rectifier blinking circuit, and therefore DC output is also derived, so the light emitting element of the photocoupler also emits light, which enters the light receiving element. , the base and emitter of the transistor are at the same potential, and the transistor is turned off. By turning off, the DC output side of the second rectifying bridge circuit becomes open, so that no AC signal is applied to the gate of the first bidirectional three-terminal thyristor, and the circuit is turned off, supplying AC power to the first load. It will no longer be possible to add it. on the other hand,
When the operation switch is turned on, a voltage is induced in the tertiary coil of the tripod transformer, and this induced voltage triggers the second bidirectional three-terminal thyristor and turns it on, supplying AC power to the second load. . Turn the operation switch to O like this.
By performing N10FF, it is possible to switch the supply of AC power to the first and second loads.

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

First, the configuration and basic operation of a tripod transformer used in an embodiment of the present invention will be explained.

As shown in FIG. 2, the tripod transformer 1 consists of an outer leg 2, a middle leg 3, and an outer leg 4 with a gap 5. The first outer leg 2 has a primary coil 6, and the middle leg 3 has a secondary coil. coil 7
However, a tertiary coil 8 is wound around each outer leg 4, and 1
When the secondary coil 6 is connected to an AC power supply and energized, a primary flux φ1 is generated in the outer leg 2.

Most of the primary flux φ1 is the magnetic flux φ in the central leg 3.

However, since the outer leg 4 with the gap 5 has a high magnetic resistance and only a very small amount of leakage magnetic flux φ1"° flows, almost no leakage flux flows into the tertiary coil 8. No voltage is induced.

Next, when the switch 9 externally connected to the secondary coil 7 is closed, a short circuit current flows through the secondary coil 7 and the central leg 3
A secondary flux φ2 in the opposite direction to the secondary flux φ1′ is generated and is shunted to the outer leg 2 as φ2° and to the outer leg 4 as φ2, and is distributed to the secondary coil 7.
Because a large amount of magnetic flux combined with the primary flux φ, which rapidly increased due to the short circuit, flows into the outer leg 4, the tertiary coil 8 wound around the outer leg 4 has 36
An alternating current voltage is induced with a phase delay of slightly less than 0°. In other words, it can be regarded as a phase that is slightly ahead of the phase of the power supply voltage waveform (see FIG. 3).

FIG. 1 is a circuit diagram of a load switching circuit according to an embodiment of the present invention, using the above-mentioned tripod transformer.

In the figure, connecting terminals e and f for connecting an external operation switch 9 and an AC input terminal of a rectifying bridge circuit 14 are connected in series to a secondary coil 7 of a tripod transformer 1. Furthermore, a smoothing electrolytic capacitor C4 and a light emitting element LD of the photocoupler PC are connected in parallel to the DC output terminal of the rectifying bridge circuit 14.

The light receiving element PT of the photocoupler PC includes a transistor Q,
This transistor Q is connected between the base and emitter of
A resistor R3 is connected between the base and collector of the transistor Q, and the emitter and collector of the transistor Q are connected between the DC output terminals of the rectifier bridge circuit 13. The AC input terminal of the rectifier bridge circuit 13 is connected in series with the resistor R2, and between the G electrode and the T2 electrode of the bidirectional three-terminal thyristor TRC. The bidirectional three-terminal thyristor TRC is connected in series with a load 11 that is always ON, and is connected to an AC power source 10.

The tertiary coil 8 of the tripod I/lance 1 includes a pair of diodes D, , D connected in parallel with opposite polarities.

bidirectional three-terminal thyristor TRC2 connected in series with
is connected between the G electrode and the T1 electrode.

The bidirectional three-terminal thyristor TRC2 is connected in series with a load 12 that is always turned off, and is connected to the AC power supply 10.

In this embodiment circuit, when the operation switch 9 is open, no AC voltage is supplied to the rectifier bridge circuit 14, and therefore the light emitting element LD of the photocoupler PC connected to the output side of the rectifier bridge 14 is supplied with an AC voltage. Since no voltage is supplied to the photocoupler PC and it does not emit light, no light enters the photodetector PT of the photocoupler PC, and thus exhibits a high resistance value between the collector and the emitter. When the light-receiving element PT of the photocoupler PC shows a high resistance value, the DC output voltage of the rectifier bridge 13 is divided by the resistor R3, and the base of the transistor Q1 becomes ten potential higher than the emitter, making the transistor Q conductive. The output side of the rectifier bridge 13 becomes short-circuited, the AC input side of the rectifier bridge 13 also becomes conductive, and the gate G of the bidirectional three-terminal thyristor TRCl is applied with the gate I-voltage in phase with T2 through the resistor R2. The bidirectional three-terminal thyristor TRC is fired, and power is supplied to the load 11 connected between terminals A, C, and C.

On the other hand, when the external operation switch 9 is open, almost no AC output voltage is induced in the tertiary coil 8 of the tripod transformer 1. Gate G of three-terminal thyristor TRC2
Since no gate voltage is supplied to the ignition circuit 12, no power is supplied to the load 12.

That is, when the external operation switch 9 is open, the load 11 is on and the load 12 is off.

Next, when the external operation switch 9 is closed, the AC output voltage of the secondary coil 7 of the tripod transformer 1 is applied to the rectifier bridge 14, and the DC output voltage lights up the light emitting element LD of the photocoupler PC. The load will cause a short circuit. As explained above about the basic operation of the tripod transformer, when the secondary coil 7 of the tripod transformer L is short-circuited by a load, 3
Next, an alternating current voltage is induced in the coil 8, and a gate voltage is applied to the gate G of the bidirectional three-terminal thyristor TRC, so the bidirectional three-terminal thyristor TRC is fired and applied to the load 12 connected in series. is powered by an AC power supply.

On the other hand, the light-receiving element PT of the photocoupler PC becomes conductive between its collector and emitter when light enters, and therefore the base and emitter of the transistor Q become at the same potential, and the transistor Q1 becomes non-conductive and the DC output of the rectifier bridge 13. side is left open, so the rectifier bridge 1
The AC input side of the bidirectional three-terminal thyristor TRC1 also becomes non-conductive, and no gate voltage is supplied to the gate G of the bidirectional three-terminal thyristor TRC1, so that the bidirectional three-terminal thyristor TRC is turned off and the power supply to the load 11 is cut off.

That is, when the external operation switch 9 is closed, the load 11 is OFF and the load 12 is ON.

(f) Effects of the Invention According to this invention, by using a tripod transformer and a photocoupler, the voltage of the secondary coil 7 of the tripod transformer, which is completely insulated from the AC power supply and is safe and low voltage, can be opened and closed using an operation switch. , the load 11 connected to the AC power supply
And the power supply to the load 12 can be switched ON and OFF alternately.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing an AC power load switching circuit according to an embodiment of the present invention, Fig. 2 is an explanatory diagram of a tripod transformer used in the load switching circuit, and Fig. 3 is an explanatory diagram of the tripod transformer used in the load switching circuit. FIG. 3 is a waveform diagram for explaining the operation of the transformer. 1: Tripod transformer, 6: Primary coil, 7: Secondary coil, 8: Tertiary coil, 9: Operation switch, 10: AC power supply, 11/12: Load, 13/14: Rectifier bridge circuit, PC: Photo Coupler, Ql: Transistor, TRC,
-TRC2: Bidirectional three-terminal thyristor.

Claims (1)

[Claims] (1) A gap is provided in one of the outer legs of the tripod core, a primary coil is wound around the other outer leg, a second coil is wound around the center leg, and a tertiary coil is wound around the outer leg with the gap, A tripod transformer having a primary coil connected to an AC power source; an operating switch having one end connected to the secondary coil of the tripod transformer; and a rectifier bridge having an AC input terminal connected in series to the secondary coil and the operating switch. A photocoupler to which a light emitting element is connected to the DC output terminal of this rectifier bridge circuit, a transistor to which the light receiving element of this photocoupler is connected between the base and emitter, and the collector and emitter of this transistor to the DC output terminal. A second rectifier bridge circuit is connected to the second rectifier bridge circuit, and the AC input terminal of this second rectifier bridge circuit is connected between the second electrode and the gate via a resistor, and a load that requires constant ON is connected in series to the AC power source. A first bidirectional three-terminal thyristor to be connected, a pair of diode circuits connected in parallel with opposite polarities and one end connected to the tertiary coil, and a series circuit of the diode circuit and the tertiary coil connected to the gate. A second bidirectional three-terminal thyristor connected between the first electrodes and connecting a load that needs to be turned off at all times to the AC power source in series.