# Center-tapped Full Wave Bridge Rectifier

I'm designing a high-voltage power supply for a plasma experiment. I have a center-tapped ignition transformer (50:1) that I'm using to step up the voltage from 120VAC to 6kVAC and then using a full wave bridge rectifier to get +/- 6kVDC. The problem is, the design of the experiment requires me to have 0 and -12kVDC outputs, not +/- 6kVDC (essentially, the positive terminal on the device I'm using needs to be grounded). My basic understanding of this concept is that I somehow have to connect the center tap of the transformer to -6kV, which is called "floating" the transformer. How can I modify the basic rectifier circuit:

to fulfill this need?

Thanks, Noah

You would have to disconnect the ground on the transformer center tap, but I would not recommend doing this because the insulation between primary and secondary (or between secondary and case/mounting) may not withstand 12 KV.

If you need 12 KV, you should get a proper 12KV power supply.

• And you would leave nothing connected to the center tap? Jul 13, 2014 at 16:12
• A: read the answer - this is likely to destroy your transformer, possibly in a hazardous manner. B: nothing on the center tap, ground attached to + side Jul 13, 2014 at 16:20
• I did read the answer, I actually bought this specific transformer in order to test whether a double-rectifier works or whether the transformer breaks. Jul 13, 2014 at 16:36
• "Breaks" is a relative term. It might spontaneously disassemble, mit spitzen sparken. You could have a fire on your hands and not be able to touch it to put it out. If you don't know the answer before you ask the question then you are asking for trouble. Apr 25, 2017 at 6:19

You could use a voltage doubler configuration on the output of your (unmodified) transformer.

I can't remember seeing this configuration used before but it should work just fine. It's two half-wave voltage doublers using a single bridge rectifier.

simulate this circuit – Schematic created using CircuitLab

• Also known as Villard voltage doubler. See my comment to the OP. Jul 13, 2014 at 16:40
• What capacitance range would be necessary for these three capacitors? Jul 13, 2014 at 16:41
• @jippie Of course I've seen the Villard half-wave scheme- but not the full-wave extension. Maybe it should be known as the Pefhany doubler. Jul 13, 2014 at 16:56
• @singerng Capacitance depends on your input frequency and current draw and required output ripple. The voltage should not change "much" with the output current in a half cycle at the input frequency. C = (Thalf_cyc * Iout)/deltaV (in Farads). Jul 13, 2014 at 16:57
• @SpehroPefhany, I don't really care about output ripple in this case, so should any capacitor value work? Jul 13, 2014 at 17:01