Mains power supply unit with surge-preventing semiconductor switch - incorporates control casing switch to commence conduction at phase determined by position of mains voltage window

摘要

A full-wave rectifier (1) supplies the load (8) via a thyristor or controlled transistor (10) with a MOSFET (11) monitoring the voltage drop between its input and output connections (12,14). A capacitor (15) connected between the load terminals (6,7) is charged through the semiconductor switch (10) if the mains supply (2,3) is switched on (9) within a voltage window of e.g. 10 V on either side of zero. Otherwise the semiconductor switch (10) remains blocked and the capacitor (15) is not charged. ADVANTAGE - Dangerous pulses of load current caused by switch-on at mains voltage phases distant from the zero-crossings are avoided.