I'm trying to use an LM317 to regulate an unregulated 30V power supply down to 27V. The power supply puts out about 36V no-load. For some reason, my circuit is just not working.
I have it hooked up just like the schematic. R1 is 1kOhm and R2 is a 500Ohm pot. The way I see it that should be adjustable from 36V down to around 8V. But I can only get the thing to output around 4V, and when I adjust the pot, the reference voltage changes. I was under the impression that the reference voltage is supposed to stay at the same ~1.2V value no matter what; that's kind of how the thing is supposed to work. Instead, when I adjust the pot, the reference voltage actually changes from like .8 to 1.2V. There's definitely something up but I don't know what it is. I have tried two LM317s. Any ideas how you could hook up an LM317 wrong to where the reference voltage would change with the pot adjustment?