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Home built variable PSU

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Gandledorf

New Member
One of the great things about working in a lab as a student was the equipment available, oscilloscopes, function generators, variable PSU's, all kinds of goodies, which I can't afford personally now that I am out because of their costs.

I've decided to try and build some myself, at least for the ones that aren't to terribly complex, (I'm imagining I'll just try and learn to do without an oscilloscope), and I decided to start with a PSU.

I have a 12V @ 500mA power supply "brick" coming in soon, and my idea was to build a variable power supply out of it, providing from 1.25 - X volts, where X is at least 9V (I'd like it to be larger, but I'm not sure what I can get out of an LM317 with a 12V PSU). Is my schematic here correct? How can I figure out how much voltage I will get out of the LM317 (trial and error I suppose? It isn't on the data sheets)

**broken link removed**

EDIT: The pot is about 2k, due to the equation for Vout being 1.25(1 + R2/R1) + Iadj
 

crust

Member
I believe they 317 needs 2-3 V of overhead from your desired voltage. The exact specifications and an example circuit to do what you desire are both in the datasheet.
 

k7elp60

Active Member
PSU

I think the 1uF capacitor on the output is the connected wrong. The + should go to the output not ground. The 0.1 should be okey if it is non-polarized. If it is polarized then it needs to be reversed also.
 
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