On Sun, 25 Aug 2013 14:34:06 +0100, Dave Plowman (News) wrote:

When building a split rail low current PS with discrete components -
like say +/- 15v - does it matter if the transformer doesn't have a
centre tap on the secondary? It's just that I've seen circuits for both
around. Some say to omit the centre tap connection to ground even if it
has one.


If your transformer has a centre tap then the best way is to use it.
(bridge rectifier to give 2 full-wave rectified supplies, earth the
centre tap).

If it has two separate windings then you can either
1) bridge rectify them individually, making 2 isolated supplies and then
connect - on one to + on the other to form a centre tap.
2) connect the windings in series (and in phase) to produce a centre tap.

If it has a single winding then the best way is probably to use a power
op-amp to produce a "virtual" centre tap. Output current is very limited
though, and you have an extra device to heatsink. This is sometimes done
for low level audio stuff as the virtual tap can be very low noise if
done properly. It is also highly accurate and will always be relative to
both supply rails.