Time-switched microwave equipment with electronic power controller - has opto-isolator in connection between time switch and mechanical switch operated by closure of door

摘要

A door interlock switch (22) is wired in series with an AC voltage capacitor (28), a rectifying diode (30) and a bias resistor (32) across the mains supply (UN). In parallel with the rectifier (30) an LED (34) transmits pulses at the mains frequency through a light-guide (36) to a phototransistor (38) in the time-switch circuit. The opto-electronic isolation prevents disturbance of the time-switching by peaks of voltage induced in the connection by switching processes taking place in the power control circuit. ADVANTAGE - Microprocessor is more surely protected by avoidance of capacitive coupling to connecting light-guide.