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.