In conventional voltage multiplier circuits, AC is used to charge the capacitors network via diodes in one cycle and discharge in the other cycle in a particular combination, which thereby produces multiples of the peak voltage. However, this circuit works on a different principle, and it is DC which is doubled. It can be used to power low current circuits.
IC555 is configured as an astable multivibrator producing rectangular pulses of about 10kHz frequency. Its output is made to drive the transistor pair T1 and T2. Transistor T2 being a pnp type, conduct when its base is negative, i.e. when the output of the IC produces a “low”. This charge C4 via diode D1 and ground (collector of T2 is grounded).
For the next pulse, i.e. when the output of IC is high, T1 conducts but T2 is cut-off, C4 cannot discharge because of diode D1. So the voltage across C4 and input voltage adds up and charge C5 via D2. Voltage across C5 will equal Vcc pulse voltage across capacitor C4 and Diode D1. Hence the operation.
However, it was found that if current greater then 50 mA and drawn, output voltage, hence regulation, is lost. Any DC voltage between 5V and 18V can be boosted (both voltage being the minimum and maximum range of the IC).
For better results, increase the value of C4 and C5 to 47 µF/40V.
Resistors (all ¼-watt, ± 5% Carbon)
R1 = 220 Ω
R2 = 6.8 KΩ
R3 = 68 Ω
C1, C2 = 0.01 µF
C3 = 0.1 µF
C4, C5 = 22 µF/40v
IC1 = NE555
T1 = SL100
T2 = SK100
D1, D2 = 1N4001