A power conserving circuit is disclosed which has a start-up circuit for initiating operation of a reference voltage generator. Included are a sensing circuit for producing a pulse signal in response to initial application of an external power source; a reference voltage generator for producing a constant reference voltage independent from an external power source voltage; and a start-up circuit for starting operation of the reference voltage generator during an interval of a pulse produced by the sensing circuit. The start-up circuit includes a switch for connecting and disconnecting the external power source to the reference voltage output port, and a voltage reducing element connected between the switch and the reference voltage output port.