Voltage Multipliers

Voltage multipliers

Voltage multipliers use clamping action to increase peak rectified voltages without increasing input transformer’s rating.

Multiplication factors of 2, 3, and 4 are common.

They are used in high-voltage, low-current applications.

i) Voltage doubler.

There are two types of voltage doublers:

a) Half-wave doubler.

During the positive half-cycle of the secondary voltage, diode D1 is forward-biased and D2 is reverse-biased.

Capacitor C1 is charged to the peak of the secondary voltage (Vp) less diode drop

During the negative half-cycle, diode D2 is forward-biased and D1 is reverse-biased.

C1 cannot discharge.

Thus, C1’s voltage adds to the secondary voltage to charge C2 to approximately 2Vp.

Under no-load conditions, C2 remains charged.

If load is added, C2 will discharge through load on the next positive half-cycle only to be recharged in the following negative half-cycle.

Resulting wave is a half-wave, capacitor-filtered voltage.

PIV across each diode is 2VP.

b) Full-wave doubler.

When secondary is positive, D­1 is forward biased and C1 charges to approximately Vp.

During the negative half-cycle, D2 is forward biased and C2 charges to approximatetly V­p.

- Output voltage is taken across the two capacitors in series.

ii) Voltage tripler

- Exactly like the half-wave doubler, but another diode-capacitor pair is added.


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