an optocoupler having a driving traic and at least one normally - on driving element couple in series to the driving triac . a light emitting element turns on the driving triac at a time when a phase of a load current is at about 0 °. the normally - on driving element is composed of either a mosfet , or optionally a relay , and an associated element for turning off mosfet , or relay , at a time when a phase of the load current is about 90 °. the arrangement prevents an inrush current or commutation failure , and provides an optocoupler which can be turned off with prescribed timing . alternative embodiments are disclosed for an optocoupler that can turn itself off when an abnormality occurs , for example , when an ambient temperature rises to an extremely high level .