Voltage Doubler:

The network of Fig. is a half wave voltage doublers. During the positive voltage half cycle across the transformer, secondary diode D₁ conducts, charging capacitor C₁ up to the peak rectified voltage charges capacitor C₁ to Vm with the polarity shown in fig. during the negative half cycle of the secondary voltage, diode D₁ is cut off and diode D2 conducts charging capacitor C₂. Since diode D₂ acts as a short during the negative half cycle, we can sum the voltages a round outside loop. On the next positive half cycle, diode D2 is no conducting and capacitor C₂ will discharge through the load. If no load is connected across capacitor C₂, both capacitors stay charged C₁ to VM and C₂ to 2Vm. If, as would be expected, there is a load connected to the output of the voltage doublers, the voltage across capacitor C₂ drops during the positive half cycle and the capacitor is recharged up to 2VM during the negative half cycle. The output waveform across capacitor C₂ is that of half wave signal filtered by a capacitor filter. The peak inverse voltage across each diode is 2VM. Another doublers circuit is the full wave doublers as shown in fig. during the positive half cycle of transformer secondary voltage diode d1 conducts charging capacitor C₁ to a peak voltage Vm. Diode D₂ is nonconduction at this time. During the negative half cycle, diode D2 conducts charging capacitor C2 while diode D₁ is nonconducting. If no load current is drawn from the circuit, the voltage across capacitors C₁ and C₂ is 2Vm. If load current is drawn from the circuit, the voltage across capacitors C₁ and C₂ is the same as that across a capacitor fed by a full wave rectifier circuit. One difference is that the effective capacitance is that of C₁ and C₂ in series, which is less than the capacitance of either C₁ or C₂ alone. The lower capacitor value will provide poorer filtering action than the single capacitor filter circuit. The peak inverse voltage across each diode is 2Vm as it is for the filter capacitor circuit. During the negative half cycle, diode D₂ conducts charging capacitor C₂ while diode D₁ is nonconducting. If no load current is drawn from the circuit, the voltage across capacitors C₁ and C₂ is 2Vm. If load current is drawn from the circuit, the voltage across capacitor C₁ and C₂ is the same as that across a capacitor fed by a full wave rectifier circuit. One difference is that the effective capacitance is that of C₁ or C₂ alone. The lower capacitor value will provide poorer filtering action than the single capacitor filter circuit. The peak inverse voltage across each diode is 2Vm as it is for the filter capacitor circuit. In summary, the half wave or full wave voltage doublers circuits provide twice the peak voltage of the transformer secondary while requiring no center tapped transformer and only 2VmPIV rating for the diodes.