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.
