How a Voltage Doubler Works
by Lewis Loflin
A voltage doubler circuit is used to produce a higher voltage direct current from a lower voltage alternating current. In its most basic form it consists of four components and is easy to build.
How it works. In the schematic above, capacitor C1 is charged through D1 every positive half-cycle. The voltage across C1 is the AC input voltage times 1.414 or about 170 volts in the case of 120 VAC input.
C2 is charged through D2 every negative half-cycle to 170 volts. The two charged capacitors are in series and the voltages add. The final voltage is 340 volts.
This will work with any AC input as long as the diodes and capacitors are the correct ratings. The 100 ohm resistor is used to limit the current surge if one uses very large capacitors and acts as a fuse. The part value is not critical.
An AC transformer secondary can also be connected as the input. I used a 25.2 volt unit to test diacs. See my Testing Diacs page.
Be very careful of high voltage shock hazards some of these circuits can produce.
Added July 31, 2011
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