Perhaps you should get a copy of the current issue (March 2007) of Nuts & Volts magazine. It has a construction article that's just begging for you to look at it. The article is "A Test Bench Power Supply". The power supply, as presented, provides two 0-20V @ 1A supplies and one fixed +5V @ 1A supply. Your other fixed supplies are easily added by using the appropriate power transformers and regulators. The regulator circuits are trivial.
They will send you a free copy to entice you to become a subscriber. (My own subscription has been ongoing since 1/80)
ok as far as it goes but you need to specify a current, line regulation, load regulation, curent limiting, crowbar protection, switching or linear, and even line voltage. also voltage range i.e. 0-30 5 - 30 etc.
my favorite? that would be 7 or 8 200w or larger NPN transistors in parallel with emitter resistors mounted on a huge heatsink driven by another 200 W transistor powered by a very large transformer into matched 30A bridge rectifiers. the main filer cap is a very large "computer" cap (ok, if you are young think of a "power stiffener" for car audio.)
the voltmeter is a large mirrored scale and "expanded" using switchable precision zeners. i.e. 0-10, 10-20, 20 -30V the ammeter is a matching large mirrored scale attached to a high current meter shunt through a multi-turn calibration pot. the meter has diode limiters to protect it from surges.
the supply can be driven from an internal or external reference. the reference source is on a separate winding and is offset several volts below common so as to achieve a zero volt output. for improved load regulation the regulator references to the output terminals. voltage is controlled via a multi-turn pot.
primarily intended for high current applications at 13.8 Vdc this unit was result after many less robust supplies became shall we say... non functional.
Electronics (ham) swap meets. Any used HP is fine. Some of the Lambda late model supplies with digital readouts have problems, but the older gear is good. None of mine have digital displays, but meters are cheap. I even have one of the HP Harrison supplies, which are stone age. Speak of the devil:
This this the Lamba that often has trouble:
Bench supplies are quite heavy. I'd sure hate to buy one on ebay unless the seller double packs it. Still, I'd get a HP supply from Ebay before building my own.
Speaking of supplies with digital readouts, I recall a chip I designed that worked fine with any bench supply except those HP with the readout. [I'd have to research to find the number.] It turns out HP put in a nice soft start feature that was so "soft" it found a flaw in my undervoltage lockout.
The site is nothing but one of those "faux" resource sites that crop up way too often in Google results stating that they have [fill in whatever terms you used in your Google search] at the right price. Sites like this must be simply collecting hits, showing the numbers to potential advertisers, and collecting $$.
If anybody has any other suggestion as to what purpose these serious-waste-of-time sites serve, I'd be happy to hear.
Assuming your 2 supplies are from isolated secondaries or separate mains transformers and the outputs will parallel, then series/isolated pair/parallel switch is easy to add to double volts or current range (single rail). If for repair or soak testing then something I would have had a use for is a presettable current monitor that sounds a sounder if the current drain goes above or below a settable amount from the initial free, ie below any current limit , current drain, for instability/thermal/intermittant fault checks
-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on
They can be a bit noisy (understatement), but PC supplies are shielded, the regulation is usually really good, and the amperage is great, as well as the efficiency compared to linear. It all depends on how much radiated noise you can accept, you can always filter the wires coming out of it.
I don't know if you find that interesting, but for my thesis in Kozani I built a high-voltage 1kV 100 mA power supply.220 V/750 V transformer(with a
6.3 V tetriary for the valves' filaments)bridge rectifier with 16 (4*4)
1n4004 (?) diodes with a 100 nF 1kV capacitor and a 1kohm bleeder across each diode, 3*450 V 100 uF capacitors, again with bleeders, switching on through the primary.Anything robust enough to stay intact to a little voltage fluctuation can be virtually supplied with a bridge rectifier and a large capacitor.
-- Tzortzakakis Dimitrios major in electrical engineering mechanized infantry reservist dimtzort AT otenet DOT gr