Progressive switching circuit for multi-element electric heating loads - uses triacs to switch main load current, with opto-couplers triggering triacs in sequence

摘要

The switching circuit uses a controller for each load, with each controller activated from a central control circuit. Each controller has an associated time delay circuit (25-30) using an oscillator (32) with a calibrating capacitor (37), and is triggered by the preceding controller operating at the end of its delay period, with the result that a cumulative delay results from first to last controller. The power switching is performed by triacs (40-45) which have their gate signals supplied through opto-isolators (53-58) to ensure electrical isolation between the power circuits and the low voltage delay circuit electronics. The switching circuit is used, for example, for multi element electric water heaters.