Please critic this power supply.

PLJack

I've been thinking about building an adjustable power supply.

Came across this one today. Link here

Right off the top I see that it needs a fuse.
Anyone see any other safety issues with this design?
Is it a sound design?
Would you feel safe building it for someone else?
If I simply swapped out T1 and U1, could it handle more than five amps(BR1)?

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- - - PLJack - - -

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Perfection in design is not achieved when there is nothing left to add.
It is achieved when there is nothing left to take away.

Post Edited (PLJack) : 9/11/2007 7:30:03 PM GMT

pwillard

This design is pretty much straight out of the Data Sheet. It's had many years of testing in the field as a result. But... 5 Amps is a limitation of the silicon and packaging on the 338.

one way to improve the current carrying capability is to stack parallel regulators as shown on the LT338 data sheet. STRONG WARNINGS about ONLY the Linear Technology devices being able to do this. See Linear Technology's data sheet.

Another way to improve the current handling would be to add higher current PASS transistors around the LM338. (Making the 338's power capability effectivly nulled and therefore you use a lower power device in it's place like an LM317)

Data Sheets are your friend.

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There's nothing like a new idea and a warm soldering iron.

RDL2004

Safety wise I would also switch both sides of the primary (use a DPDT switch) and ground the case if it's metal. As far as the circuit itself, you can do much better.

I would get the datasheets for the LM317 and LM350 from National Semiconductor and study some of their suggested circuits. With variable power supplies, the biggest problem at higher amps is often heat from power dissipation due to high voltages from the transformer being dropped to relatively low output voltage by the regulator. Don't design for higher output voltage than you really need, or look at maybe a dual secondary transformer with a series/parallel switch to avoid having to burn off too much voltage with the regulator.

edit: I found this once I got home from work, it's from a National Semi data sheet.



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- Rick

Post Edited (RDL2004) : 9/12/2007 12:29:41 AM GMT

pwillard

I forgot to mention... I've had a lab power supply using this design on my workbench since 1984. Still Kicking.

FYI: It makes a LOT of sense to use a high quality 10 turn potentiometer for the 5K Ohm Part.· I never regretted spending the extra cash on the one in my supply.

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There's nothing like a new idea and a warm soldering iron.