By use Timer IC highly popular the number NE555 and other equipment a little again. It can give current get about 50mA convenient for the circuit, that use low current the small-sized.
The principle works of the circuit be. When use Volt input 12VDC give with the circuit will touch Filter current smoothly with increasingly.
The capacitors C5 give with IC1, The resistor R1,R2 and , capacitors C1, Which build the circuit model astable multi vibrator Square wave generator, at the frequency about 2KHz come out the way pin 3 of IC1.
By have capacitors C3,C4 diode D1 and D2. Which build be boost up voltage x 2,which will enhance the level Volt out be the direct current about 24VDC or 2 times of the level Volt input.