Bridge Rectifier Voltage Doubler

I'm designing a generic PSU board, and want to have an optional voltage doubler on a jumper.

I found this topology, which I think will be simpler to reconfigure with a couple jumpers than topologies 2 and 3 (in the next two posts).

Only thing is.. I've never seen it done this way before. Will it work as advertised?

"Regular" voltage doubler.

Other way.

That first scheme is WIDELY used in PC power supplies, to get ~~300V DC from either 110V or 220V lines with a simple switch/jumper.

Using a 2PDT switch and using the other half of it to put the two unused diodes (the ones which end in parallel with the caps) to the other AC input would make them share the current, the overall temp will be the same but I thing diodes may thank you if they are on the smallish side for the task.

JS

Awesome, thanks PRR. I guess it's time to download Spice so I can sim it myself next time. 

I've got my jumpers configured so C1 and C2 are switched into parallel when the doubler is inactive (4x upgrade for capacitance, since C1 and C2 in series with no doubler will halve capacitance).

joaquins said:

Using a 2PDT switch and using the other half of it to put the two unused diodes (the ones which end in parallel with the caps) to the other AC input would make them share the current, the overall temp will be the same but I thing diodes may thank you if they are on the smallish side for the task.

JS

Click to expand...

Joaquin,

Do you mean putting the bottom two diodes in parallel with the top two diodes by connecting the "south" pole of the diamond to the "north" pole?

Dylan W said:

joaquins said:

Using a 2PDT switch and using the other half of it to put the two unused diodes (the ones which end in parallel with the caps) to the other AC input would make them share the current, the overall temp will be the same but I thing diodes may thank you if they are on the smallish side for the task.

JS

Click to expand...

Joaquin,

Do you mean putting the bottom two diodes in parallel with the top two diodes by connecting the "south" pole of the diamond to the "north" pole?

Click to expand...

That's right. As I said if the diodes are overkill there is no advantage, but since you will have bigger peak currents in the doubler to be able to get the same power that may help.

The following is not for your case but to have in mind in case of playing with this configuration at higher voltages, don't get confused with this, just informative... For the series caps is recommended to add a resistor divider in parallel so you ensure half voltage in each cap. Since you only have 12V and you are going to configure the caps in parallel you need each cap to be able to handle the 12V, probably 16V caps. In that case you won't need those resistors since the leakage of the caps already makes them to sit in some point between the rails and you won't have more than 12V on any cap. When working with 300VPS you probably use ~200V caps, so you won't switch the caps in parallel and you need to ensure half voltage on each cap. Since leakage is not the same for all caps a bleeding resistor is connected in parallel with each cap, which value should be much lower than the equivalent leakage of the cap.

JS

The diode current is the same in either case. (Transformer can only do so much.)

Diode PIV changes, but PIV is cheap for most applications.

A many-pole/throw switch is less elegant than a single pole or jumper.