[sdiy] Power Supplies

[Rob Spencer]

Hi All,

I’ve been thinking a lot about power supplies recently and was after some 
advice…

The first PSU I built was the classic 7812/7912 with a nice toroidal 
transformer which sat at the back of the nice big case I was using, 
however I’m now trying to slim things down. I’m also keen to remove mains 
power from the box completely.

I’ve been having a look using buck converters in an inverting 
configuration so I could use a 15v DC input, however I would prefer to 
stick to linear, as switching PSUs don’t quite feel right for me in 
analogue audio applications. I’m now toying with the idea of doing the 
heavy lifting in a PSU enclosure and then bringing the Dual 12v in through 
a multipole connector.

During my research I stumbled across this post: 
http://www.electronicspoint.com/threads/what-is-a-dual-tracking-regulator-f
or.3354/ which talks about a "dual tracking regulator" adjusting both 
voltages so they remain the same potential difference with respect to 
ground. If one voltage drops the other will be adjusted by the same 
amount, which got me thinking….

If I have the classic 7812/7912 PSU, then run a 7805 of the +12v, load it 
up with an assortment of digital and analogue modules from a variety of 
designers, I would expect the loading on each rail to be different. As I 
approach the 1A mark, the voltages on each rail will be quite different 
with respect to gnd. The affect this will have on critical audio op amps 
will be supply voltages not sitting evenly around zero volts, which, I 
would have thought, would produce a signal either with a DC offset or some 
other kind of distortion.

It would be great to incorporate a “dual tracking regulator” to ensure the 
voltages remains the same level to ground, but they all appear to be rated 
in the 100s of mA. Is it possible to use a power transistor to draw a 
larger current from rectified, but unregulated supply, limited to the 
regulated voltage or are there other tried and tested solutions to the 
overall problem?

Many thanks in advance.

Rob
www.gmsn.co.uk

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