Voltage Doubler

 

Voltage Doubler

A voltage doubler application is a DC power supply capable of using either a 240 VAC or 120 VAC source. The supply uses a switch-selected full-wave bridge to produce about 300 VDC from a 240 VAC source. The 120 V position of the switch rewires the bridge as a doubler, producing about 300 VDC from the 120 VAC. In both cases, 300 VDC is produced. This is the input to a switching regulator producing lower voltages for powering, say, a personal computer.

 

Half-Wave Voltage Doubler

The half-wave voltage doubler in Figure 1(a) is composed of two circuits: a clamper shown in (b) and a peak detector (half-wave rectifier) in (c). C2 has been added to this peak detector (half-wave rectifier).

 

Figure 1. Half-wave voltage doubler (a) is composed of (b) a clamper and (c) a half-wave rectifier.

 

Half-wave Voltage Doubler Operation Circuit Analysis

Referring to Figure 1(b) above , C2 charges to 5 V (4.3 V considering the diode drop) on the negative half cycle of AC input. The right end is grounded by the conducting D2. The left end is charged at the negative peak of the AC input. This is the operation of the clamper.

During the positive half cycle, the half-wave rectifier is shown in Figure 1 (c) above . Diode D2 is out of the circuit since it is reverse-biased. C2 is now in series with the voltage source. Note the polarities of the generator and C2, series aiding. Thus, rectifier D1 sees a total of 10 V at the peak of the sinewave, 5 V from the generator, and 5 V from C2. D1 conducts waveform v(1), as illustrated in Figure 2, charging C1 to the peak of the sine wave riding on 5 V DC - Figure 2 v(2). Waveform v(2) is the output of the doubler, which stabilizes at 10 V (8.6 V with diode drops) after a few cycles of sine wave input.