[sdiy] power supply pain

[Tony Allgood]

Hi all,

I tend not to use regulators in series unless the second one is very low
current. A typical application would be 7815 and then a 7805 for the +5V
at 10mA. If the currents were going to be similar, ie. 500mA each, then
you must really take them separate. This way the total power dissipation
would shared nicely between them.

But I also use well chosen power resistors too, this way you have a
third dissipating element. But you need to know your maximum current is
through the dropper resistor. It doesn't affect regulation much. And it
can have the effect of allowing you to build a low pass filter too on
that rail. Useful for those noisy +5V lines.

Using a second transformer is useful too, but it can be bulky even with
the little toroids available today. BUT, how about this... getting a
custom made transformer made. Its not that expensive, I think I paid for
a custom 12-0-12 @ 500mA 5-0 @ 1A design around 50UKP. OK, its a bit
pricey but if its the only thing that will fit, it may be the only
choice you have. I used Drake in the UK, but there are plenty of others.

OR... you could wind your own. Done that, worked very well, but terribly
boring if you have a toroid. It takes ages and the maths can be a bit
heavy.

Regards,

Tony Allgood  Penrith, Cumbria, England

Oakley Modular Synth and TB3030:
www.techrepairs.freeserve.co.uk/projects.htm
My music: www.mp3.com/taklamakan