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dgta 29th June 2011 07:15 AM

Simple dual PS
 
I need a simple/inexpensive PS, +/- 0 to 35-40V at 1A max. Performance is not crucial, as far as noise, ripple, etc. as it will be used only for initial test of circuits I build or gear I repair. Current limiting would be nice. Questions:

Is there a simple way to get a 317 and 337 to track together? I mean, track a bit closer than using a 2-gang pot, and without using a dozen opamps :)

Is there a single chip variable dual regulator? External pass devices would be OK.

What about a switcher? I'm thinking those cheap Chinese ones on eBay would do fine if they could track. Does anyone know if any of the chips used in those boards have slaving capability?

Mooly 29th June 2011 07:59 AM

This doesn't really answer your exact question but for initial testing of power amps etc I don't think you can't beat a "normal" PSU and bulb tester with various bulbs on hand. Have resistors to discharge the rails as soon as power is off. Use a modestly rated transformer, and that too provides a good measure of current limiting in the event of a short. Simple, tough and cheap.

Commercial dual PSU's are available at reasonable price and perhaps come up on eBay too,

DIGIMESS|HY3003-2|DIGIMESS BENCH PSU DUAL 0-30V | CPC

Andy5112405 29th June 2011 08:10 AM

There's a simple design here Tracking Dual Supply Schematic Diagram Definition | Schematic Circuit Diagram

sofaspud 29th June 2011 08:24 AM

A LM317 with an output series resistor divider and virtual ground can get you close to +/- 0-20 volts. Two pots on the adjust pin can give you coarse-fine control. Tracking is built in. A 1A slo-blo fuse is easy current limiting.

dgta 29th June 2011 08:58 AM

Andy, that circuit looks promising but the opamps won't work at +/-40V. Are there any wide-use (i.e. cheap and available) opamps that work at +/-40V? I want to stay away from exotic stuff.

Sofaspud, I'm not sure exactly what you are describing, but I need a minimum of 0 to +/-35V, not 20.

Andy5112405 29th June 2011 10:03 AM

If you do a search on Google for dual rail stabilised PSU you can get lots of ideas.

sofaspud 29th June 2011 10:04 AM

Just offering an option. A +/-35V 1A tracking regulator is fairly exotic on it's own I would think. My little search for a "70V op amp" took me to National's LM3886!

Mooly 29th June 2011 11:55 AM

Quote:

Originally Posted by sofaspud (Post 2623005)
A LM317 with an output series resistor divider and virtual ground can get you close to +/- 0-20 volts. Two pots on the adjust pin can give you coarse-fine control. Tracking is built in. A 1A slo-blo fuse is easy current limiting.

Actually a virtual ground is a really good idea...

The whole thing can then be as simple as a single rail supply, say 80 volts, feeding a high gain darlington pair with a simple pot on the base. That give you 0 to 80 volts adjustable. It doesn't need have regulation for simply powering up amps etc. Current limiting can be the "text book" low value resistor and transistor to give limiting... use a low value preset across the sense resistor and you have variable current limiting too.

To get the split supply you have a discrete darlington "virtual earth" generator across the output giving a split supply from whatever you feed it with...

dgta 29th June 2011 05:04 PM

OK, I found it. The OPA454 goes to +/-50V, so I can implement Andy's suggestion. I think that's as simple as it gets.

A virtual ground is OK as long as the load is balanced. I can't count on that, since I'm building it for general use, not a specific application.

Still chewing on the idea of two cheap switchers if I can figure out how to get them to track. I like the idea of minimal dissipation at large Vout-Vin settings.

Thanks all for the help.

Mooly 29th June 2011 06:07 PM

An active virtual ground doesn't need balanced loads :)


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