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LM317 Faulty?

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New Member
I had 2 LM317 adjustable voltage regulators running side by side producing 5v and 12v off a single 13v supply. They both had their own pass transistor to boost the current output. But now ive done something (not sure what) and the voltage output keeps dropping.

If i have one of the regulators setup by itself to regulate at 5v and i pump 12v into it will produce 5v, but when i put a load on it the voltage drops to 3-4v. Does that mean its stuffed? What could have caused this?

Also when i have both 5v and 12v circuits working at the same time and i place a load on the 5v circuit the output voltage of the 12v reg drops to 3v.


Active Member
If the unloaded input DC voltage 13V, this is too low for 12V output reg. working. When the load on 5V out. increased and 12V drastically dropped, the input power too low and maybe the buffer condenser capacity not enough or transformer output voltage and/or current low.
Attach a sematic for proper answer.


New Member
lm317 regulator

:D hi fletcher,

i believe in order for the 317 to operate properly it has to have at least an input of 2v higher than the desired output. 13v is not enough to make it work properly. also how about the resistor connected to the current adjust pin, is the value of the resistor set for 12v output?

better yet, post the schem of your project for proper evaluation. :D


New Member
hi there,
i hope you've done something to keep the LM317 cool enough to work properly :?
otherwise, if you want to have an output of 12V/5V and you can't get the LM317 running as you want, just take an 7812 / 7805!
cya sankt-seibel
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