a relay driver circuit is disclosed in which a relay coil is operated by enabling the collector - emitter path of a switching transistor . in order to avoid damage to the transistor from voltages induced in the relay coil when the relay is turned off , an isolating semiconductor device is inserted between the transistor and the relay coil . this semiconductor device is operated in synchronism with the driving transistor and thus isolates the driving transistor from transients during the de - energization of the relay .