The voltage rating of capacitors is determined solely by the
type of multiplier circuit. In the half-wave doubler circuit of
figure 1A., C4 must be capable of withstanding a maximum
voltage of Vm, while C2 must withstand a voltage of 2 Vm. In
the full-wave doubler circuit of figure 1B., both C1 and C2
must withstand voltages of Vm. The half-wave voltage tripler
of figure 1C. requires C1 to withstand a voltage of Vm, and
both C2 and C3 to withstand voltages of 2 Vm. A good rule of
thumb is to select capacitors whose voltage rating is
approximately twice that of the actual peak applied voltage.
For example, a capacitor which will see a peak voltage of
2 Vm should have a voltage rating of approximately 4 Vm.