Control circuit for triacs

Details Control circuit for triacs Control circuit for triacs

1989-07-24

1991-07-30

Zazworsky, John

Electrical transmission or interconnection systems

With nonswitching means responsive to external nonelectrical...

Temperature responsive

307262, H03K 17292, H03K 17725

Patent

active

050362348

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

The invention deals with a direct current controlled trigger or control circuit for triacs connected via a consumer circuit to a source of alternating current supply voltage.
For power control of consumers of alternating current networks, triacs are used in increasing numbers. Traics provide in the simplest manner the full wave operation of the consumer with the phase cut off, since only a single control power element is required. At a predetermined angle of each half wave the triac must therefore be ignited.
A great number of circuits which produce ignition pulses suitable for ignition of triacs are known and require a different amount of structural elements. An arrangement for phase cut off control is disclosed in the DE-OS No. 24 03 097. With the known control circuit the current for loading a load capacitor is adjustable such that--in dependence upon the direct control current voltage--the resistance of the drain-source-channel (r.sub.DS) of a field effect transistor is changeable. For coupling the half waves, two resistors are used in a bridge circuit with the field effect transistor, and serve for the symmetrization of the current flow angle of the positive and negative half waves.
A disadvantage of the known control circuits is the fact that relatively many structural elements are required which on the one hand increase the expenses and the space requirements and on the other hand increase the reliability risks.


ADVANTAGES OF THE INVENTION

The inventive circuit arrangement the advantage that the quantity of structural parts is considerably reduced and thereby the manufacturing expenses and the costs of the switching arrangement are lowered. Moreover, in advantageous manner junction layer-field effect-transistors (JFET) or insulating layer-field effect transistors (MOSFET) can be used, which are price favorable and operationally reliable.
It is especially advantageous when with MOSFET-transistors the gate is electrically isolated from the channel to provide the free selection of the potential between the control circuit and the switching circuit of the arrangement.


DRAWINGS

An embodiment example of the invention is shown in the drawings and illustrated in the following description.


DESCRIPTION OF THE EMBODIMENT EXAMPLE

A network alternating current voltage U.sub.N at the terminals 10 and 11 is applied via a consumer 1 to the load path of the triac 8. Parallel to this load path, there is connected a series circuit composed of the load resistor 2 and the capacitors 3, 4 and 5. The model points 18 and 19 form respectively the connecting points of the triac 8. The model point 14 which lies between the load resistor 2 and the load capacitor 3 is connected via the diac 9 with the gate of the triac 8. Furthermore the model point 15 lying between the capacitors 3 and 4 is connected with one end of the drain-source channel of a field effect transistor 7, while the other end of the channel is connected with the model point 18. The gate of the field effect transistor 7 is connected with the model point 16, which is formed by the joint connection of the capacitors 4 and 5. Simultaneously the direct current control voltage U.sub.ST is supplied via resistor 6 from the terminal 12 to the model point 16. The control voltage U.sub.ST is supplied at the terminals 12 and 13.
The operation of the circuit arrangement is described below.
In the blocking phase of the triac 8, in other words at the beginning of each half wave of the network voltage U.sub.N, the load capacitor 3 is loaded via the load resistor 2 and via the combination of the series connected capacitors 4 and 5 the channel of the field effect transistor 7. When the sum of the voltages of the capacitors 3, 4 and 5 reaches the breakdown voltage of the diac 9, then the diac abruptly becomes conductive and supplies an ignition pulse to the gate of the triac 8. The triggered triac 8 remains conductive till the half wave of the network voltage again reaches zero. The capacitors 3, 4, and 5 are also almost completely discharged

REFERENCES:
patent: 3676706 (1972-07-01), Laupman
patent: 3840800 (1974-10-01), Laupman
patent: 4321480 (1982-03-01), Miles
patent: 4331914 (1982-05-01), Huber

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