Mike Dinolfo mdinolfo at EROLS.COM
Sat Feb 19 13:36:03 EST 2000

regarding your voltage doubler circuit:

I would guess that 100 ufd for each of the two caps in a voltage doubler
circuit would be fine, for maximum loads of 10 ma.  The formula for
discharge of a capacitor is I = C x dv/dt, which is pretty easy for me
to apply to any "conventional" full-wave or half-wave circuit, but which
I've never been able to figure out how to apply to voltage doubler or
multiplier circuits (maybe someone else on the listserver can help?
hint, hint...)

For a voltage doubler circuit, the maximum (i.e., no-load) voltage will
be 6.3 x 2 x 1.414 - 2 x Vd, where Vd is the typical forward voltage
drop of a rectifier diode (probably about 0.7 volts with these
currents), giving about 16.4 volts no-load.  I'm guessing that a 10 ma
load current will result in a voltage dip between charging cycles of
maybe 2 or 3 volts, to a (minimum guesstimate) value of  13.4 volts.  Of
course, it won't be regulated.  If you need regulation, and you want to
use a "conventional" 3-terminal 12 volt regulator, you might want to
consider a voltage tripler circuit, to ensure enough "headroom" for the
regulator circuitry.

Hope this helps some.

Mike Dinolfo

> Joe Sloss wrote:
> Does anyone have a favorite circuit for a voltage doubler power supply
> using 6.3VAC (w/ one side grounded) to develop 12VDC at 5 or 10 MA?
> There are schematics in the Handbook but unfortunately no component
> values.  I would imagine that 100+ MFD or so would be sufficient for
> the two filter caps.  Thanks,  Joe

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