Voltage Quadrupler : A voltage quadrupler circuit is shown in fig. which provides output voltage V0 = 4 Vm.
Operation : Capacitor C_{1}, C_{2} and C_{3} charges to Vm, 2Vm and 2Vm respectively. In the second negative half cycle, C_{4} charges through forward biased diode D_{4}. Voltage across C_{4} wil be the net voltage due to supply and C_{2}, C_{3 }and C_{1} which is respectively as. So c_{4} charges through D_{4}, C_{3}, C_{1} and C_{2} to 2Vm volt with left plate positive now if we take output across C_{2} and C_{4} we get V0 = 4 Vm which is fout times the maximum value of input a.c. hence the circuit is called as voltage quadrupler circuit.
Voltage quadrupler circuit has following features:
(1) Peak inverse voltage rating of each diode is 2 Vm.
(2) Ripple frequency will be twice the supply frequency if load is connected.
(3) Such circuits are used in CRO for CRT anode voltage.
(4) One disadvantage of such circuit is that as more and more capacitor diode sections added, the output voltage keeps on falling substantially.