CS261358B1 - Wiring for thyristor switches in AC circuits - Google Patents

Abstract

The solution concerns a circuit for controlling thyristor switches in alternating current circuits. The circuit is designed in such a way that a triac is connected between the control electrodes of the switches, which, after switching in the control electrode circuit, switches a current pulse into the control electrodes of the thyristor switches. The current pulses are divided into individual thyristors by a quadrature diode.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention

At present, thyristor switches are mainly controlled by a pulse transformer circuit. This control method is very energy intensive: the primary winding of the transformer requires pulses of a series of amperes. This energy remains unused and is lost by dissipative processes in the transformer core. Impulse transformers are therefore relatively large and structurally demanding, or? it is necessary to galvanically separate three windings with different potentials. The switching of the current pulses in the region of the primary circuit places high demands on the switching element, usually a transistor, and on a source of uniform supply current. High power pulse transformers bring! phase distortion caused by nonlinear processes in the core of these transformers. The material for cores of high power pulse transformers is usually silicon steel.

These drawbacks are overcome by the circuitry for controlling the thyristor switches of the invention, which is based on the fact that the triek is connected by its anodes to the thyristor control electrodes via two diodes connected by a cathode to these control electrodes. At the same time, the triac is connected to the output terminals of the antiparallel connected thyristor switches via two additional diodes, which are connected by cathodes to the triac anodes.

The advantage of the wiring is that the energy for control of the control electrodes is already taken from the controlled circuit and switching the triac requires current pulses of the order of tens of milliamperes.

In the accompanying drawing, the circuit according to the invention is shown. No power output terminals 10, 11 are connected against each other two thyristors 6, 7. Their control electrodes are connected to the triac anodes 1 via the first and third diodes 2, 3. · Triac anodes 1. are connected to the power output terminals 10. 11 via the second and fourth diodes 4, 5. Control pulses are applied to the triac control circuit 1 at the input terminals 8, 9.

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The function of the circuit according to the invention is as follows: if there is zero voltage between the input terminals 8, 9, the trunk 10 is closed and the current does not pass through the control electrodes. The circuit between the output terminals 10, 11 is in the open state of the switch. By applying a control current pulse to the input terminals 8, 9, the triac 3 is brought into a conductive state. Applying positive resp. a negative voltage to terminal 10 against terminal 11 passes current through the first output terminal 10 - fourth diode 5 - triac 1, - first diode 2 - control electrode of the first thyristor 6 - second output terminal 11, respectively. output terminal 11 - third diode 4 - triac JL - fourth diode 3 - second thyristor 7 - into a conductive state and current is no longer passed through the control circuit. The circuit between the output terminals 10, 11 is in the closed state of the switch.

The phase delay between the control pulse between the input terminals 8.9a and the switching state between the input terminals 10 is given by the switching time of the triac 1 and diodes 2, 3, 4, 5. The switching time of the triac 1 is one to two orders shorter than the switching time of the power thyristors. 6 _t and 7. the control current of the triac allows using pulse transformers of small ferrite cores. The number of turns in the transformer winding is of the order of tens of turns. Only low-power transistors without pulse transformer or integrated circuits can also be used to switch the current pulses, the zero potential of the switching pulse source being connected to the second input terminal 9.

Wiring for control of thyristor switches can be used in thyristor welding machines, asynchronous motor controllers, asynchronous motor soft-start circuits, and generally in AC phase control circuits.

Claims (1)

Circuit for controlling thyristor switches in alternating current circuits, characterized in that the first input terminal (8) is connected to the triac control electrode (1), the first anode of which is connected to the second input terminal (9), and to the cathode of the second diode (4) and at the same time anode of the first diode (2), the cathode of which is connected to the control electrode of the first thyristor (6) connected by the anode to the first output terminal (10) and the cathode to the second output terminal (11); (1) is connected to the cathode of the fourth diode (5) and to the anode of the third diode (3), the cathode of which is connected to the control electrode of the second thyristor (7) connected by its cathode to the first output terminal (10); (5), and with its anode at the second output terminal (11) and at the same time at the anode of the second diode (4),