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Voltage Multiplier

All voltage multipliers convert an input AC voltage into an output DC voltage some multiple of the source.

Basic

Note

There are many other forms of voltage doublers, but this is the one I learned and it's called a Delon circuit.

Using a pair of half-wave rectifier circuits in series, we can create a voltage doubler. Technically, it's a full-wave rectifier (both halves of the input are used), but operating wth a ripple frequency twice the AC frequency (120Hz in the US).

Schematic of Delon voltage doubler

The voltage (DC) on the right-hand side will be double the input (AC) voltage.

Cockroft-Walton

If we extend the idea of the basic voltage multiplier, we can create something even more interesting: a Cockroft-Walton generator. This is basically a form of charge pump, and is not designed to deliver large current just high voltage.

Note

I did not draw this because Fusion360 doesn't let you easily put parts at 45 degree angles, and I'm too lazy to design new parts pre-rotated. These are taken from this article.

Cockroft Walton generator

This shows a generator with 4 doublers. If we have 5VAC in and 5 stages we can calculate the output voltage of the multiplier using this (and ignoring diode drops):

\[\begin{aligned} V_{out} &= 2NV_p \\[10pt] &=2\times 4 \times 5\\[10pt] &=40 \mathrm{VDC} \end{aligned}\]

The output voltage (\(V_{out}\)) is twice the peak input voltage (\(V_p\)) multiplied by the number of stages (\(N\)). If we add in the typical diode drop (0.7V), then we're not quite getting 2x gain, we're getting \(2\times(5 - 0.7) = 8.3\), giving us a total of 33.2V

Comments or Questions?

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