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Power Supply Schematic Advice

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bryan

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I have one of those economical digital power supplies that one commonly finds on eBay. Not the greatest in terms of quality and it has an unusual design where the voltage can suddenly increase when the current is adjusted.

So I wanted to gut it, and replace the internals with my own power supply. Was going to re-use some of the components ie, display, case, transformer, switches fans, maybe some of the large caps etc. I was wondering what everyone thought of this 0-30v schematic.

Any issues that you can see, does it look like a good design?. One point that is confusing is the reference to L1 and L2, they don't give a value for the inductors. Any suggestion on what type one could use.

**broken link removed**
 
Tony's stuff is usually good. I always liked the LM723 because of its flexibility. Read up on Astron power supplies, which are based on the 723, and used by a lot of hams, including me.
 
The inductors are described in part 3. I like he 723 regulator too. A 723 based supply I have doesn't like being back fed. Most supplies don't.
 
Oh boy, the LM723. My eyes glaze with nostalgia......... as my very first project that included an IC and that actually worked was a power supply with a LM723 and an analog voltmeter, a 15-pound transformer and "computer grade" filter capacitors, the size of a small beer cans. Applying (and smearing all over the place) thermal compound to the TO3-case transistors and its mica insulators attached to a hefty heatsink.

As other people have mentioned, the LM723 was quite crude for today's standards and had several limitations. However, it had all the essential building blocks for a variable PSU, and its limitations required that one read carefully and understood properly the data sheets and app notes.
Also... lots of experimenting whereas perhaps a pair of LM723s and several output 2N3055 transistors would be blown up.

No simulators. Only paper, pencil, and a scientific calculator like a Texas Instrument's SR71.

Once that you had a proper working supply, you could actually claim to be a "power supply designer".

And crowbars....there was always a real possibility that one of the series pass transistors would short out, and it could take out expensive equipment connected to the PSU. Crowbar design was a black art itself, too slow a response and would'nt do any good. Too fast, and one would have nuisance tripping.
 
Seems a lot of the schematics for variable power supplies stil use the 723, must still have some value out there. Any examples out there of a better design. 0-30v up to 5-10 amps.
 
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