# Voltage Doubler

Discussion in 'Electronic Basics' started by Jay, Nov 21, 2004.

1. ### JayGuest

I have a design for which I need to generate a high DC voltage (more than
400V). My power source for this voltage is the UK mains (230Vrms @ 50Hz).
The way I see it is that I have 2 options. The first option is to use a
step up transformer and a bridge. The transformer would need a ratio of 1:2
(primary: 230V, secondary: 460V). As I cannot find any off the shelf
transformers I would need to wind my own. My second option is to use a
simple voltage doubler consisting of 2 capacitors and 2 diodes. The output
of the voltage doubler would be something close to 460V DC.

Out of the 2 options the voltage doubler seems the most straightforward.
Some questions I have on this setup are:

1) Does the transformer option offer any advantage over the voltage doubler?
2) How can I determine the maximum current that can be drawn from the
voltage doubler?
3) Is connecting a voltage doubler directly to the mains a good idea?

If you have any opinions or advice on this subject then please share them.

Thank you.

2. ### John LarkinGuest

There are two configurations. One makes +2*V to neutral, the other
makes +V and -V. "Full wave doubler" and "Half-wave doubler."
650, theoretically, a bit less with diode and capacitor losses. 230
VRMS is 650 peak-to-peak.
That's too complex to do for free. Bigger caps allow more current. How
much do you need?
Depends on the hazards. Might be ok if you're careful as to which line
is neutral.

What's the application?

John

3. ### peterkenGuest

might use an inrush current limiter to safeguard your setup if using 230Vac
as input
might think of fusing the output (PTC or fuse)
be very carefull if using mains directly, for personal security

4. ### GarethGuest

Actually, the voltage doubler could, depending on the current you draw
and the size of the capacitors, give you an output of twice the peak
voltage (230V is the RMS value). This could be closer to 650V.

2 * 230 * sqrt(2) = 650V

Don't forget that the capacitors could remain charged after you
disconnect the mains. Be very careful.

Gareth.

--

5. ### cornytheclownGuest

Looks like you could find a suitable transformer if you hunted around
at some sources that carry old tube type radio equipment. They would
have 460 volt output or close transformers........also.....couldnt a
person use a microwave oven transformer and strip off some of the
secondary windings till he got the desired output ???

6. ### Steve EvansGuest

Theyre not built for continuous duty. You could try two in parallel.

7. ### Bob MastaGuest

You might look for dual-primary transformers, designed to
allow easy conversion between 120V and 240V systems.
In normal use for 240V, you would put the two primaries in series.
current is small compared to the transformer rating), or hook them
in parallel with the proper polarity to get double the output
voltage.

Just a thought.

Bob Masta

D A Q A R T A
Data AcQuisition And Real-Time Analysis
www.daqarta.com

8. ### John LarkinGuest

Either case will make the transformer saturate and catch fire.

John

9. ### Rich GriseGuest

If you're rewinding it, just add a few turns to the primary.

Cheers!
Rich

10. ### Rich GriseGuest

Yes - it's less likely to kill you.
It has to do with capacitor values and how much ripple you can tolerate -
I'd have to look up the formula, but one of the experts probably has it on
Usually no, unless you have very good isolation.
OK.

Good Luck!
Rich

11. ### Bob MastaGuest

Don't run it that hard next time! ;-)

Bob Masta