Electronics > Beginners

Alternative size current sense resistor

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queennikki1972:
How do you feel about this circuit?

5A constant current constant voltage regulator

http://www.circuitstoday.com/few-lm317-voltage-regulator-circuits

MosherIV:
How do I feel about it?

 :-/O
Difficult.
I am impressed controlling both V and current limit can be done with LM317.

Do you understand how it works?

It needs 3 voltage rails, Vin, V+ and -6V.
The volt adjust and current limit is not that easy to understand.
It may not be easy to add panel meter to show the set voltage and/or set current.

If you just want to build a bench psu - this may work.

Does it help your understanding - only you can answer that.

MarkF:
If you use a rail-to-rail or single supply op-amp, I believe you could make it work with lower output voltage range.  Maybe worth trying anyway.

Kleinstein:
The current limit is usually set by the resistor and the set voltage to drop at the resistor at most. Going from 10 Ohm to 0.1 Ohms is a large change, getting current 1000 times higher. So the math in the initial posting is wrong.

Adding a variable current limit to a LM317 or similar voltage regulator is difficult to get good. It is usually easier to start with a combined constant current / voltage regulator with an external power transistor. So more like using an LM723 or 2 OPs and a  reference. A lab supply is a rather common topic - with plenty of poor quality circuits around.

AVGresponding:
Using a single supply certainly makes things easier; the original design would have needed 4 power rails, with the +/- rails for the op-amp needing to be fairly well regulated if you want to avoid oscillation, which given the AC coupling of the feedback on the op-amp is likely to make your load regulation, shall we say, 'poor'  :scared:

It may be also a better idea to use something like an L200 instead of an LM317, as it's specifically designed to have variable current regulation, and uses the same TO220 package, albeit a 5-pin variant. It also has a TO3 version, much as the LM317/337 etc do with the K series.

The ST datasheet includes example circuits with extended current capability using a pass transistor, and doesn't include AC coupling in the feedback circuit...

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