We saw in the Rectifiers tutorial that the rectifier’s DC output voltage is lower than the mains input voltage. The Voltage Multiplier, on the other hand, is a type of diode rectifier circuit that can produce an output voltage that is many times greater than the applied input voltage .
TA basic symmetrical voltage multiplier circuit made up of two half-wave rectifier circuits is shown above. We can increase the output voltage of a standard half-wave rectifier by a set amount by adding a second diode and capacitor to its output.
Because one of the diodes conducts in each half cycle, similar to a full wave rectifier circuit, this type of voltage multiplier configuration is known as a Full Wave Series Multiplier.
Capacitor C1 charges up through diode D1 when the sinusoidal input voltage is positive, and capacitor C2 charges up through diode D2 when the sinusoidal input voltage is negative. The output voltage 2VIN is measured across the two capacitors in series.
Although the voltage produced by a voltage multiplier circuit is theoretically unlimited, they are typically designed to increase the voltage by a factor of less than ten due to their poor voltage regulation and low current capability.
He Rectifiers tutorial, we learned that the DC output voltage controlled by the rectifier is lower than the mains input voltage. The Voltage Multiplier, on the other hand, is a type of diode rectifier circuit that can produce an output voltage that is many times greater than the applied input voltage.
Although a voltage transformer is commonly used to increase voltage in electronic circuits, a suitable step-up transformer or a specially insulated transformer required for high voltage applications may not always be available. A diode voltage multiplier circuit, which increases or “steps-up” the voltage without the use of a transformer, is an alternative.
In many ways, voltage multipliers are similar to rectifiers in that they convert AC to DC voltages for use in a variety of electrical and electronic circuits, such as microwave ovens, strong electric field coils for cathode-ray tubes, electrostatic, and high voltage applicationsSo, how does it function? A half-wave voltage doubler is shown in the circuit.
Diode D1 is forward biassed and conducts charging up the pump capacitor, C1, to the peak value of the input voltage during the negative half cycle of the sinusoidal input waveform (Vp).
Due to the lack of a discharge path for capacitor C1, it remains fully charged and acts as a storage device in series with the voltage supply. Simultaneously, diode D2 conducts through D1, charging up capacitor C2.
Diode D1 is reverse biased during the positive half cycle, preventing C1 from being discharged, while diode D2 is forward biased, charging capacitor C2. However, because the voltage across capacitor C1 is already equal to the peak input voltage, capacitor C2 charges to twice the input signal’s peak voltage value.
In other words, V(positive peak) + V(negative peak), so D1 charges C1 to Vp on the negative half-cycle, and D2 adds the AC peak voltage to Vp on C1 and transfers it all to C2 on the positive half-cycle. C2 discharges the voltage across the capacitor through the load, preparing for the next half cycle.
The voltage across capacitor C2 can then be calculated as Vout = 2Vp (minus the voltage drops across the diodes, of course), where Vp is the input voltage’s peak value. This double output voltage is not instantaneous; rather, it gradually increases with each input cycle, eventually settling at 2Vp.
Because capacitor C2 charges for one half of the input waveform, the output voltage discharged into the load has a ripple frequency equal to the supply frequency, thus the name half wave voltage doubler.
The disadvantage is that, similar to a half wave rectifier circuit, it can be difficult to smooth out such a large ripple frequency. Capacitor C2 must also have a DC voltage rating that is at least twice the peak input voltage.
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