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 (V_p) 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 2V_p.

– 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 2V_P.

b) Full-wave doubler.

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

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

- 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.