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stable constant current generator with LM317

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fuzzzy

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lm317 constant current

In one of my circuits i'm using a constant current generator LM317 configuration to provide 100mA 12V power supply. I have a problem: during operation LM317 become hotter and it changes current output. I'd like to have a stable output current. Could you please suggest me a way to compensate this error?
 

constant current generator

The LM317 regulator is compensated for wide range of temperatures, so it is possible that the problem lays in the resistor that you use as the current sensor ..
You may try two things:
- use resistor rated for higher power, say, 1W ..
- lower the input voltage which is fed to the LM317, and by doing this you will lower the power converted into heat in the LM317 .. Also, you may consider adding a heatsink ..

Regards,
IanP
 

lm317 constant current circuit

I don' t think it's shunt resistor! If i keep lm317 cool by a fan current raise again. I'm using a 1,5A lm317 for 100mA from 12V. I think i should use an heatsink. but what do you think if i use LM338 or LM350. They're rated for 3A or 5A so they can hardly get hotter.
 

lm317 operation

If i keep lm317 cool by a fan current raise again.
Click to expand...
Sounds like the thermal shutdown ..
In the same conditions the other regulators (LM350 and LM338) may behave in the same way .. Their current rating is valid only if you ensure sufficient heat transfer off the IC structure ..
So, try to keep the IC's temperature down by adding a heatsink ..

Regards,
IanP
 

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