Protection circuit for AC switching of transformer loads - has memory elements to control circuit by detection of current direction

摘要

The protection circuit has a memory element (FF1) supplied by a battery (DB) coupled to a diode (TD) and a control stage (SV) that delivers a signal (ZS). The a.c. switch (WS) has a light emitting diode (LD), zero crossing detector (ZD) and a thyristor (TP) coupled to an external thyristor pair (ET). An input to the diode (LD) is from a flip flop (FF2). The memory elements serve to latch the direction of the current signals and provide interruption of the a.c. voltage to prevent overload. ADVANTAGE - Protects against overload or over saturation in transformer supplies.