In article ,
"Dave Plowman (News)" writes:
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.

Depends on the nature of the load.

If the load draws exactly same current on both rails, no current will
flow in the 0V connection, and in theory it's not needed. In practice,
this is very unlikely.

If the load can draw different currents on the two rails, then a current
will flow in the 0V connection. If there's no centre-tap on the
transformer, this current in the 0V rail will need to be passed to the
opposite rail, wasting power in the power supply. If the difference in
rail currents is small, this probably doesn't matter. If it's big,
the the power supply will have to start dissipating/wasting larger
amounts of power, and in that case a design which can use a centre-
tapped transformer will be more efficient and run cooler.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]