IMPROVED SYSTEM FOR TRIAC TRIGGER CONTROL IN COMBINATION WITH A SENSING ELEMENT

摘要

The invention relates to a circuit of the kind wherein a load (L) is supplied via a triac (TC) with current from an AC voltage supply source (A, B) under the control of a triac control means (IC) in combination with a sensing element (RT). In previous circuits the sensing element is energised by a current from a DC source which is derived by rectification and smoothing of the alternating current of an alternating voltage supply source, which has limitations in integrated circuitry. In the present invention the sensing element (RT) is energised by an alternating current to produce a sensed alternating current. The triac control means (IC) includes an integration means (6) for producing a control signal which is representative of the integral of the difference between a value corresponding with the average peak to peak magnitude of the sensed alternating current and a reference value. The triggering or otherwise of the triac (TC) being determined by a latch (LCH) actuated in response to the magnitude of the control signal relative to one or more threshold levels. The present invention may be used in thermostats or other sensing devices.