Need a 12.6 VDC power supply schematic

[woody]

This device may require a minimum load current to function properly. I believe that
minimum load is 10ma. If you are powering it up without a load then the current through rr2 and rr3 may be below this minimum value. You might try just shorting
rr2 or placing a load on the output to se if this is the problem.

[tomchr]

Originally Posted by Andy5112405

I think your Vin is too low, the LM317 needs about 3V to operate. As an experiment try increasing Vin, try about 18VDC that should prove the point.

Yeah... The National Semiconductor LM317 has a worst-case drop-out of about 2.5 V. I.e. the input voltage has to be at least 2.5 V higher than the output voltage. Allowing for a few volts of ripple, an input voltage of 18~20 V seems reasonable.

You also need a reasonably sized heat sink on the LM317. If the chip overheats, it'll enter thermal shutdown.

Three bad pots?! Actually, that sounds like you either didn't hook the components up according to the schematic or there's a cold solder joint somewhere.

~Tom

[tomchr]

Originally Posted by Dmeister

It seems the trim potentiometer wasn't properly working. Well, actually, not one, but THREE of them ! I am that unlucky. I bought a proper trim potentiometer so now it works.

Do you get 12.6 V out now?

~Tom

[tomchr]

Originally Posted by woody

This device may require a minimum load current to function properly. I believe that
minimum load is 10ma.

Actually, it's a bit lower than 10 mA typically. It depends on (Vout-Vin). See the datasheet for details.

With 120 ohm from OUT to ADJ, you already draw 10 mA through the regulator. No additional load needed for regulation.

~Tom

[Dmeister]

Yes, I can now adjust the output voltage with the trim potentiometer. It could have been a cold joint, I guess. I'm still not a master at soldering . And yes, I have a small heatsink mounted on it. Thanks for the help everyone !