Voltage Doubler

Voltage Doubler is the kind of voltage multipliers , they use clamping action to increase peak rectified voltages without the necessity of increasing the transformer’s voltage rating. There are  two types of voltage doublers:

  1. Half wave voltage doubler
  2. Full wave voltage doubler

First we see Half wave voltage Doubler here:

Half wave Voltage Doubler and Its Operation:

A voltage doubler is a voltage multiplier with a multiplication factor of two.  A half wave voltage doubler is shown in below diagrams.  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 the diode drop with the polarity shown in part (a) circuit diagram.  During the negative half cycle , diode D2 is forward biased and D1 is reverse biased, as shown in part (b) circuit diagram. Since C1 can’t discharge, the peak voltage on C1 adds to the secondary voltage to charge.  C2 to approximately 2Vp. Applying Kirchhoff’s law around the loop as shon in part (b) , the voltage across C2 is

Vc1 – Vc2 + Vp = 0
Vc2 = Vp + Vc1
Neglecting the diode drop of D2 Vc1 = Vp therefore.
Vc2 = Vp + Vp = 2Vp 
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(a) During Positive cycle , operation of Half wave voltage doubler

 
 
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(b) During Negative Half cycle, operation of Half wave voltage doubler

 Under a no-load condition, C2 remains charged to approximately 2Vp.  If a load resistance is connected across the output, C2 discharges slightly through the load on the next positive half cycle and is again recharged to 2Vp on the following negative half cycle.  The resulting output is a half wave, capacitor filtered voltage.  The peak inverse voltage across diode is 2Vp.

Full wave Voltage Doubler

A full wave doubler is shown in circuit diagram (c & d).  When the secondary voltage is positive D1 is forward biased and C1 charges to approximately Vp as shown in circuit diagram  (c), during the negative half cycle, D2 is forward biased and C2 charges to approximately Vp, as shown in circuit diagram (d).  The output voltage, 2Vp is taken across the two capacitors in series.

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(c) Full wave voltage doubler operation during positve cycle

 

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(d) Full wave voltage doubler operation during negative cycle


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