Mark Fortune said:
I would need the option of both +v and -v in respect to ground, but only
sometimes at the same time (ie when testing audio circuits, but not when
doing logic circuits) if I switched one of the secondary windings off...
would I still be saving half the power?
Wastage is becoming more apparent as I read more and more posts... and am
considering rethinking to a more energy efficient design now.
I was (originally) thinking big heatsink with some thermal controlled
fans screwed on.
switching psus I know nothing about, but think I will research this. Any
good places to start (apart from the obvious google)?
This might be a good candidate for a triac phase fired circuit such as:
http://www.st.com/stonline/products/literature/an/3566.pdf
These can be noisy, but they are very efficient, and low in cost.
If you want to make your own transformer,
www.toroid.com has transformer
kits. I think a 1.4 kVA core (available in 120 or 120/240) is about $100. I
have used that same core (actually 4 of them) to build a transformer rated
at 5.6 volts at 1000 amps continuous. I used bus bar for the secondary. You
can do the same thing with an old Variac. However, it is a tedious process
to wind a high voltage winding. The 1.4 kVA core has 0.7 volts per turn, so
you'd need nearly 90 turns for each of your 60 volt outputs.
Most importantly, consider exactly what you need the supply for, and build,
buy, or modify according to the exact specifications you actually require.
You must look at efficiency, weight, size, line and load regulation, max
and min voltage adjustment, ripple, noise, overshoot or droop on load
change, response time, cost, and time to design, build, and troubleshoot.
You can get so much high quality equipment on eBay and at electronic flea
markets, that building your own is usually only for very special
requirements or as a learning experience.
For logic circuits, I would recommend a separate 5 VDC (or 3.3, etc.)
designed for that purpose, with a good crowbar overvoltage protection
circuit. A wide range adjustable bench supply can too easily generate a
spike that will wipe out (or incrementally damage) all the logic circuits.
It might be a good idea to put a crowbar on the logic board.
Good luck,
Paul