On Nov 28, 9:23*pm, MarkAren wrote:
Hi Guys,

Ages ago I saw a very simple circuit - a CT transformer, couple of
caps, 4 rectifiers and a change over switch.

With the switch in one position, the circuit was a bridge rectifier,
in the other, a voltage doubler.

Pointers please, I have forgotten where I saw this...

Thanks,

Mark

Just draw a standard bridge rectifier circuit, bridge across the full
transformer secondary, filter capacitor at the bridge output. Now--
break the connection from the capacitor (-) to the bridge, and put in
a SPDT switch, wiper to the cap (and to ground, if you will) and the
two possible connections to either the bridge negative output, or to
the transformer secondary center tap. There's no problem connecting
to the transformer center tap with the bridge (-) floating. You can
also use this basic circuit to supply two voltages at once: connect
up a bridge circuit, and ground the bridge/cap (-), and also put a cap
from transformer CT to ground. The bridge output (peak) will be
nominally 1.4* the RMS transformer full secondary (minus a couple
diode drops), and the CT output will be half that. Or, you can ground
the CT and have + and - nominally equal voltages, assuming the loads
on both sides are similar.

Cheers,
Tom