Here the active voltage doubler schematic diagram:
This circuit drives relays of 24 and 18VDC from a 12V power supply. Use this circuit with almost any PNP or NPN power transistor.
U1_______: NE555 timer C1,C2____: 50uF/25V Q1_______: TIP29, TIP120, TIP61, TIP110, 2N4922, 2N4921 Q2_______: TIP30, TIP125, TIP62, TIP115, TIP125, 2N4918
