Three-phase load control. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Clocks, timers, relays, load switches
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A simple device, the diagram of which is shown in Fig. 1, can be successfully used to control a three-phase load.
(click to enlarge)
The level of interference generated by the device is reduced by synchronizing the opening time of the triacs for each of the phases with the moment the voltage passes through zero. Control over all three phases is carried out jointly with the help of series-connected optocouplers. However, with separate supply of control signals to the optocouplers, it is possible to independently control the load in each of the phases. If separate phase control is not expected, you can get by with one optocoupler by connecting its leg to pins 12 of all microcircuits.
The power supply of the device with a voltage of about 10 V (with a maximum output current of 18 ... 20 mA) is formed by diodes VD1, VD2, a zener diode VD3, capacitors C1 ... C3 and resistor R1. In order for the triacs to open at moments close to the voltage transition of the corresponding phases through zero, pulse shapers are used, synchronized with the mains frequency and made on transistors VT1, VT2 and resistors R2 ... R4. With a positive half-cycle of the mains voltage, the transistor VT1, connected according to the circuit with a common emitter, is open and saturated - the voltage on its collector is close to the emitter (transistor VT2 is closed). With a negative half-cycle, transistor VT1 is closed, but transistor VT2, connected according to a common base circuit, is open and saturated, and the voltage on its collector has the same sign and amplitude. At moments when the voltage in the corresponding phase is less than 40 ... 50 V in absolute value, both transistors are closed, and the voltage on their collectors is close to the voltage at the terminals of 7 microcircuits.
As a result, pulses with a frequency of 1.3 Hz are formed at the input of the DD100 element, the fronts of which practically coincide with the moments when the phase voltage passes through zero. The output 12 of the element DD1.3 receives a signal from the optocoupler U1, and thus, the corresponding control pulses are generated at the output of the element.
The device is mounted on a board made of foil fiberglass with dimensions of 110x75 mm (Fig. 2).
Plus power supply to the conclusions of 14 microcircuits is connected by a separate conductor. The device uses MLT resistors, any small-sized capacitors for the corresponding voltage.
Transistors KT361 can be replaced with KT502. Instead of AOT128 optocouplers, almost any transistor ones will do. Optocouplers AOU103V can be replaced by AOU115V, however, in this case, you will have to change the design of the printed circuit board.
Author: V.E.Tushnov
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