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How do I set up a voltage regulator? Answered

What is the connection ADJ in this image of a voltage regulator stand for? Is it just the ground, or something else?



Best Answer 9 years ago

The bottom line is ground. The adjust pin has to connect to a voltage divider, between output and ground. The regulator continually adjusts its output to keep the voltage drop across R1 equal to 1.25V. So if R2 = 0, the output of the regulator is 1.25V. If R2=R1, the output would be 2.5V. The formula works out to Vout=1.25V * ((R2/R1)+1).

If you connected Adj pin directly to ground and omitted both R1 and R2, I imagine the output would be 1.25V.

Hmm... after giving it some thought, I imagine the ADJ pin could basically be considered the ground pin of a 1.25V fixed regulator. I suppose if you set up a voltage divider on the ground pin of an LM7805, you could get an adjustable output where Vout= 5V * ((R2/R1)+1). I'll have to try that. I love when I learn something accidentally through answering a question. :)

Yep, that works as a quick and dirty fix. You lose a bit of regulation though. Better to use a zener.

That voltage regulator is adjustable, that's what ADJ stands for.