Vehicles employing idle reduction system need a step up DC-DC converter which operates stably for a voltage drop of a battery during engine restart. This paper proposes a power supply for idle reduction employing a ripple regulator having an excellent transient performance and stability without using electrolytic capacitors, which results in long life. The feedforward circuit is employed in order to improve transient response for input voltage change. The experimental results revealed the basic characteristics of the proposed converter, which has a good transient response.