A circuit arrangement, to which the vehicle electric system supply voltage is applied and which for briefly maintaining at least one internal normal d.c. voltage in the event of failure of the vehicle electric system supply voltage, includes a reserve energy accumulator, to which a charging voltage higher than the at least one internal normal d.c. voltage is applied in regular operation, and which, in the event of failure of the vehicle electric system supply voltage, delivers a reserve voltage with which operation of at least some electronic circuits may be maintained for a limited period of time, and it includes at least one step-down regulator which steps down the applied input direct voltage to the at least one internal normal d.c. voltage.