JPS5821925A - Alternating current switch circuit - Google Patents

Abstract

PURPOSE:To obtain a miniature and inexpensive AC switch circuit which is capable of the control of a gate circuit with a switch element of a low level of breakdown strength, by providing a switch element and a switch controlling circuit to the gate circuit of a triac. CONSTITUTION:A gate circuit which controls the ON/OFF of a triac 17 consists of a loop circuit including a current controlling resistance 19, a light emitting diode 20, a switch element 35 and a power supply circuit 40 and set between a terminal T1 of the triac 17 and a terminal of the gate G. The opening/closing of the element 35 is controlled by the latch output given from a switch controlling circuit 300 provided at the front stage of the element 35. Thus the gate current of the triac 17 is controlled. At the same time, a gate current is flowed to a P-N junction consisting of the terminal T1 and the gate G. As a result, the current of high voltage can be controlled for a main circuit by means of a switch element of a low level of breakdown strength.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an AC switch circuit used as an output circuit of a programmable controller (PC), and in particular switches a triac using a gate circuit including a logic circuit that is DC isolated from the outside. Related to AC switch circuits.

2. Description of the Related Art Conventionally, triacs have been used in PC output circuits, particularly as switch circuits that open and close the current of a load inserted in series with an AC power source. The triac is controlled to turn on and off the current shunted by a resistor, a switch element, and a gate resistor connected in parallel with the triac by opening and closing the above-mentioned switch, which is controlled separately from the low voltage side circuit. This controls the load current.

FIGS. 1 and 2 show examples of the above-mentioned conventional AC switch circuits. This is an AC power battle. The current of the load 8 connected in series with the triac 5 connected in series with it is 0N-
This is for OFF control.

1 and 2, the configuration of the gate circuit of the triac 5 is different. In FIG. 1, the alternating current across the triax 5 is connected to the bias resistor 13a and the gate resistor 1'8.
After rectification by the rectifier 4 via the optical thyristor 3b
light emitting diode 3 installed on the - next low voltage) side.
By controlling the light emission of a, the current of the gate circuit of the triac 5 is controlled, and the triac 5 is controlled to turn on and off. In Figure 2, the gate circuit in Figure 1 uses a rectifier 4 and one optical thyristor 3b, but instead of the rectifier, two optical thyristors a b and a b' connected in anti-parallel are used. It is composed of In addition, a data register 1 is provided on the fifth side of both circuits, and its output is connected to the light emitting diode 3 via a driver 2.
It is driving a. In the figure, 12a and 12b are the bias resistor and bias capacitor of the optical thyristor 8b, respectively, 11 is a protection diode, 10 is a light emitting diode for output display, 6 is a surge voltage absorbing element, and 7 is provided at a rate of one for multiple circuits. This is the fuse that was used.

In general, a PC controls a controlled object such as an external machine or a production line by controlling a plurality of outputs using a combination of a plurality of inputs according to a predetermined program. Therefore, FIG.
It is used as the output part of a point (circuit) or 128 point PC.

Therefore, reducing the price of input/output circuits will have a significant impact on reducing the price of the entire PC. When looking at the above conventional circuits from the viewpoint of cost reduction, the relatively expensive rectifier 4 and optical thyristor 3 (Fig. 1) or the optical thyristors 18b and 13b (Fig. 2') in which the two are connected in antiparallel are used. )- is required for each output circuit, and a high-voltage optical thyristor is required, making it difficult to reduce the price with the above circuit diagrams (Figures 1 and 2) as they are. it is conceivable that.

Also, regarding the method of displaying the 0N-OFF operating state of the output circuit, in the conventional circuit, the display diode I
Since O is provided in series with the light emitting diode 3a on the primary side of the optical thyristor, it does not necessarily directly display the operating state of the output element (TRIAC).

The present invention has been made in view of the above points, and includes a switch element in a triac gate circuit and a memory section in the preceding stage thereof, and a photocoupler is used to transfer control signals and serial data between the memory section and the PC control section. The purpose of this invention is to reduce the cost of a multiple output circuit by reducing the number of photocouplers used and by creating a configuration in which the gate circuit can be controlled by a switch element with low withstand voltage. Furthermore, by configuring the structure so that a light emitting diode can be connected directly to the gate circuit of the triac, the ON-OFF state of the triac can be directly displayed.

Hereinafter, the AC switch circuit of the present invention will be explained in detail with reference to the drawings.

FIG. 8 is a one-output circuit diagram of the AC switch circuit according to the present invention, including a block diagram in part.

A load 15 connected in series to an AC voltage source vAc (ACloov) is connected to an individual terminal 50b and a common terminal 50a that constitute a pair of terminals on a terminal block 50, and a main current circuit is formed by a fuse 16 and a triac 17 connected in series. Configure. In order to absorb surge voltages, a surge voltage absorption circuit 18, which is usually a composite component in which a capacitor and a resistor are connected in series, is connected in parallel with the triac I7. Common terminal 5
0a is provided for each output (for example, 4 outputs), and protects against overcurrent for each output using fuses 16 connected in series. The gate 1-(G) terminal of the triac 17 is connected to a control circuit element 30 including a switch element 35 via a current limiting resistor 19 and a light emitting diode 20 for output display. Therefore, the gate circuit for ON-OFF control of the triac 17 is a loop circuit consisting of a current limiting resistor 19, a 20° light emitting diode switch element 35, and a power supply circuit 40 between the T1 terminal and the gate (G) terminal of the triac 17. It is configured. The switch element 35 is configured to be opened and closed by a latch output from the switch control circuit 3oo provided in the preceding stage, and controls the gate current of the triac 17 to switch the current of the main circuit.

In this circuit, the T1 terminal of triac 17 and the gate (
G) Since the main circuit of the triac is controlled by passing a gate current through the PN junction made up of the terminals, it is possible to control the high voltage current of the main circuit using a switch element with a low withstand voltage. It is. For example, 'r,
-c terminal forward voltage VPN (approximately 0.7V), ON voltage VON across the switch element 35, resistance value of the resistor 19 R, and gate current Ig, the power supply voltage E of the gate circuit is , Eg=IgR+VPN+VON. Ig-30mA, R-120Ω, VPN=0
．． 7V-VON=0.8V+7), Eg=4.6V
Therefore, sufficient control is possible with an IC drive voltage of 5-V.

Moreover, if the breakdown voltage of the switch element is at the level of the breakdown voltage of a normal element, it will be sufficient. From this, the switch element 35
The control circuit of the gate circuit, including the gate circuit, can be easily integrated into an IC as well as an ordinary IC, which in turn contributes to lowering the cost of the entire switch circuit.

Furthermore, by inserting the display light emitting diode 20 in series with the gate circuit of the triac 17, the ON-OFF state of the triac 17 can be displayed more directly than in the conventional circuit.

In the above circuit configuration, the switch control circuit 300 is
For example, it temporarily stores a drive control signal for the load 11 output from a program controller (PC), and by supplying this stored control signal to the switch element 35,
It controls opening and closing of the switch element. In other words,
When a signal for making the switch element 35 conductive is output from the switch control circuit, a gate current of the triac 17 flows, which turns the triac 17 ON, and current flows to the load 15 to drive it. At this time, the light emitting diode 2o emits light to indicate that the triac 17 is in the ON state.

Next, a switch control circuit 3o is provided before the switch element 35 and controls opening and closing of the switch element.

An example of the configuration will be explained in detail with reference to FIG. In this configuration example, a portion including the switch control circuit 3oo and the switch element 35 surrounded by the dotted line is made up of one control IC 80. IC80 used for this switch control circuit
data transferred serially from outside the IC, especially the PC
A shift register 31 converts and outputs the load drive signal from the shift register into parallel data, a latch circuit 32 temporarily stores the parallel data from the shift register, and the storage output of the latch circuit and the data transferred from the outside (especially a PC). AND gate 33, OR gate 34, and OR gate 34 for logically ANDing and ORing the clear and strobe signals.
The switch element 85 is driven by the output of the switch element 85.

In this circuit diagram, an open-drain MOS transistor is shown as the switch element 35, but an open-collector transistor may also have a gate current (for example, 80%
Any device that can control a current of more than mA) can be used. A plurality of control signals and serial data signals from an external control unit or the like are input from the input terminal 22 through the photocoupler 39 to the control IC 30 in an electrically insulated state. Control signal input terminal 22 and photocoupler 8
9 is composed of a plurality of numbers.

In this embodiment, the serial data input 22a, the clock input 2
2b, a light emitting diode driver 38a corresponding to the five input terminals of the latch input 22C, the strobe input 22d, and the clear input 22e.

88b, 88c, 38d, and 38e are provided, and corresponding photocouplers 89a, 89b, 89c, 89d,
39e is provided.

Therefore, the serial data (serial data for load control) input from the input terminal 22a is transferred to the shift register 31 from the terminal 37a of the control IC 80 via the photocoupler 39a.
supplied to At this time, the serial data supplied to the shift register 81 is sequentially shifted according to the clock signal from the input terminal 22b, and the serial data supplied to the shift register 31 is, for example, 3
Data for 2 bits is stored. Then, the data stored in the shift register 31 is transferred to the latch circuit 32 by the latch input, and the data is temporarily stored. The storage output from the latch circuit 32 is output from the AND gate 38. The opening and closing of the switch element 35 is controlled via the OR gate 34. If a clear signal is supplied, the outputs of the OR gates will all be the same regardless of the storage output of the latch circuit 32, and the switch element 35 will be in a closed state, for example.

In this embodiment, since the shift register 31 that outputs serial data in parallel via the isolation photocoupler 8j is provided on the control IC side, even though a plurality of control signals are input, the conventional output is Compared to conventional circuits, the output circuit can be constructed with fewer photocouplers as a whole, and the cost of the output circuit can be lowered compared to conventional circuits. That is,
Hot turnip? The number of error BSs is constant, and by increasing the capacity of the shift register and the capacity of the latch circuit, it is possible to cope with the input of a plurality of control signals.

Next, a circuit example of the power supply circuit 40 in the embodiment circuit example of FIG. 8 is shown in FIG. 5, and the power supply circuit 40 will be explained. In the figure, one end of the AC power supply VAC is connected to one end of the primary winding of a power transformer 41 via a protective fuse 42, and the other end is connected to the other end of the power transformer 41, forming a secondary circuit. do. The voltage induced on the secondary winding side of the electrically insulated transformer 41 is rectified by a rectifier 43, smoothed by a capacitor 44a, and then connected to a constant voltage circuit consisting of a Zener diode 45b, a transistor 45a, etc. 45 and is supplied as a power source to the control IC 30 and the like. Furthermore, in this embodiment, the power for the gate circuit of the triac 17 is supplied from the smoothed voltage section after full-wave rectification, but this depends on the type of switch element 85 used in the gate circuit and the gate of the triac 17. It is determined by the current.

Depending on the switch element used, the voltage after passing through the constant voltage circuit 45 may be supplied. (For example, when using a transistor as a switching element, 5V is possible.) Triac opening/closing control is of course possible by passing a continuous DC current as the gate current, but it is also possible by passing a pulsed current. be. The pulse width and duty differ depending on the load, but when the load is a solenoid that is often used as a load for a programmable controller (PC), the pulse width is 10 μsec.
, a pulse current with a duty of l/40 is sufficient to control the current.

Therefore, if the size of the power transformer 41 is controlled by pulse operation, a small one can suffice.

FIG. 6 shows a control ICAO with 82 outputs.
1 is a block diagram showing an embodiment of the present invention. FIG.

A serial data signal supplied from the input terminal 22 together with a control signal is inputted to the control IC 30 via a photocoupler 39. Here, the Morokuchi Road (31°32.83.84)
After being converted to parallel output data by
7 gate circuit. A surge absorption circuit 18 is provided in parallel with the triac 17, and its output end is connected to the terminal block 5.
0 and are respectively connected to external loads.

As is clear from the above explanation, according to the present invention, the number of isolation photocouplers can be reduced by inputting a serial data signal to a series input parallel output shift register provided in the gate circuit of a triac isolated by a photocoupler. By providing a gate circuit isolated from the low-voltage side circuit between the T1 terminal and the gate terminal of the triac, ON-OFF control of the triac can be performed using a switch element having a normal withstand voltage. Further, by using pulse operation in combination, it is also possible to reduce the power supply capacity of the gate circuit. Furthermore, since the display light emitting diode can be inserted directly into the gate circuit of the triac, it is possible to more directly display the ON-OFF state of the triac.

Therefore, by implementing the present invention, it is possible to achieve integration, miniaturization, and cost reduction of AC switch circuits. Since the present invention requires a common power source and photocoupler, a larger cost reduction effect can be expected as the number of output circuits increases.

[Brief explanation of the drawing]

Figures 1 and 2 are examples of conventional AC switch circuits. FIG. 3 is a circuit diagram showing a specific example of the AC switch circuit implemented in the present invention, FIG. 4 is a circuit diagram of the control section of the AC switch circuit of the present invention, and FIG. 5 is a circuit diagram of the power supply section according to the present invention. FIG. 6 is a block diagram showing an embodiment of the present invention in the case of 32 outputs. 15; load, 17; triac, 19; current limiting resistor, 20; light emitting diode for output display, 22; control data input terminal, 30; control circuit element, 800; switch control circuit, 81; shift register, 82; latch circuit, 3
5: Switch element, 40: Power supply circuit. Agent Patent Attorney Aihiko Fukushi

Claims (1)

[Claims] 1. In an AC switch circuit that drives and controls a load connected in series to an AC power supply by ON-OFF control of a triac inserted in series, the triac connected to the gate terminal of the triac is connected to the gate terminal of the triac. 0N-OFF
a shift register that outputs in parallel control signals that are serially input from the outside via a photocoupler, a latch circuit that temporarily stores the parallel outputs of the shift register, and an output of the latch circuit that drives the switch circuit. An AC switch circuit comprising a drive circuit and switching the triac by controlling opening and closing of the switch circuit. 2. The AC switch circuit according to claim 1, characterized in that a light emitting diode for output display is inserted in series with the gate terminal of the triac.