CONTROL CIRCUIT INITIATING CONDUCTION OF AN OPTO- ISOLATOR UNIT

摘要

CONTROL CIRCUIT INITIATINGCONDUCTION OF AN OPTO-ISOLATOR UNITABSTRACT OF THE DISCLOSUREA control circuit for turning on an optical iso-lation unit only when an input signal is at least of a givenmagnitude or threshold level. The circuit exhibits a resis-tive input below the threshold level and a constant currentcharacteristic above the threshold. An arrangement oftransistors is provided to bypass the opto-isolator belowthe threshold and to drive the opto-isolator with substan-tially constant current above the threshold.