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Voltage Multiplier Circuits

Form Super Practical Electronics


It is often useful to have a rectifier circuit that is capable of producing a dc voltage that is higher than the zero-to-peak voltage of the ac source. Although the usual procedure is to use a transformer to step up the voltage before the rectifier stage, an alternative approach is to use a voltage multiplier circuit.


Figure 1. Conventional doubler voltage                                             Figure 2. Charge Pump Doubler Voltage



The top circuit shown here (Figure 1) represents a conventional voltage doubler. During a positive half cycle,D1 is forward biased, allowing C1 to charge to a dc voltage of V0 (the peak source voltage). During the negative half cycle, D2 is forward-biased, and C2 charges to V0. Because C1 and C2 are connected in series with their polarities aiding, the output voltage is the sum of the capacitorsí voltages, or is equal to 2V0.


The second circuit (Figure 2) shown is a variation of the first and is called a charge pump. During the negative half cycle, the source pumps charge into C1 through D1 with D2 open-circuited, and then during the positive half cycle,D1 becomes an open circuit and D2 becomes a short circuit, and some of the charge in C1 flows into C2. The process continues until enough charge is pumped into C2 to raise its voltage to 2V0. One advantage of the charge pump over the conventional voltage doubler is that one side of the source and one side of the output are common and hence can be grounded. To obtain a larger voltage, additional stages can be added, as shown

within the bottom two circuits. A serious limitation of voltage-multiplier circuits is their relatively poor voltage regulation and low-current capability.


Warning !!!

-Use the higher capasitor voltage capacity

-Use the higher Diode voltage capacity




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