Voltage Doubler Circuit or Cascaded Voltage Multiplier Circuit
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| Figure A |
- Both full wave and half wave rectifier circuits produce a dc voltage less than the ac maximum voltage.
- When higher de voltages are needed, a voltage doubler or cascaded rectifier doubler circuits are used.
Working of Cascaded Voltage Multiplier Circuit :
- Suppose B is more positive with respect to A and diode D1 conducts thus charging the capacitor C1 to Vmax with polarity as shown in Figure A.
- During next half cycle terminal A of capacitor C1 rises to Vmax and hence terminal M attains a potential of 2 Vmax.
- Thus the capacitor C2 is charged to 2 Vmax through D2.
- Normally voltage across the load will be less than 2 Vmax depending upon the time constant of circuit C2RL.
T1, T2 – High Voltage transformer
C1, C2, C3, C4 capacitors
T – Isolating transformer.
R1, R2, R3, R4 –
Rectifiers or diodes
RL = Load Resistance
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| Figure B |
- Cascaded voltage doublers are used when larger output voltages are needed without changing the input transformer voltage level (as shown in Figure A and B)
- The rectifiers R1 and R2 with transformer T1 and capacitors C1 and C2 produce an output voltage of 2V in the same way as described earlier.
- This circuit is duplicated and connected in series or cascade to obtain further voltage doubling to 4V.
- T is an isolating transformer to give an insulation for 2 Vmax. since the transformer T2 is at a potential of 2 Vmax above the ground. The voltage distribution along the rectifier string R1, R2, R3 and R4 is made uniform by having capacitors C1, C2, C3 and C4 of equal values.
- AC input voltage waveform (1)
- AC output voltage waveform with capacitor filter. (2)
- Since the max DC output voltage waveform with capacitor filter. (3)
Figure C
Disadvantage of Cascaded Voltage Multiplier Circuit :
- Cascaded voltage multiplier circuits for higher voltage are cumbersome and requires to many supply and isolating transformer.