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Old 29th June 2011, 06:15 AM   #1
dgta is offline dgta  United States
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Default 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?
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Old 29th June 2011, 06:59 AM   #2
Mooly is offline Mooly  United Kingdom
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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
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Old 29th June 2011, 07:10 AM   #3
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There's a simple design here Tracking Dual Supply Schematic Diagram Definition | Schematic Circuit Diagram
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Old 29th June 2011, 07:24 AM   #4
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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.
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Old 29th June 2011, 07:58 AM   #5
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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.
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Old 29th June 2011, 09:03 AM   #6
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If you do a search on Google for dual rail stabilised PSU you can get lots of ideas.
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Old 29th June 2011, 09:04 AM   #7
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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!
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Old 29th June 2011, 10:55 AM   #8
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Quote:
Originally Posted by sofaspud View Post
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...
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Old 29th June 2011, 04:04 PM   #9
dgta is offline dgta  United States
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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.
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Old 29th June 2011, 05:07 PM   #10
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An active virtual ground doesn't need balanced loads
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