APPARATUS AND METHOD FOR SWITCHING PROVIDED WITH REINFORCED RELAY LIFE

摘要

PURPOSE: To provide a relay contact life that is further reinforced against an inductive load as well as a resistive load by inputting a low voltage AC control input to a microprocessor, along with input from an AC common to the IRQ input port of the microprocessor. CONSTITUTION: An AC input signal is coupled to the input port of a microprocessor via a current limiting resistance. AC ground is also connected to the IRQ port of the microprocessor. The output port of the microprocessor is connected to a relay driver to turn a fan on and off. A control circuit calibrates itself continuously and periodically, reads an AC input at its peak synchronously, and either switches the actual-time clock of the microprocessor non-synchronously on the basis of a relay or switches it synchronously by imparting a selective delay so that engagement and disengagement of contacts occur in the vicinity of the zero cross of an AC line voltage waveform.