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What is the max input current for the lm317? Answered

I am having trouble understanding the datasheet. Is there a max input current for the lm317? If so, what is it? I want to supply 4A input current to it from a laptop power supply.
http://www.fairchildsemi.com/ds/LM/LM317.pdf
Thanks.

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steveastrouk

Best Answer 7 years ago

The 317 won't LET you draw more than 1.5 A from it, and it will automatically shut down if it gets too hot.

Steve

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Dmxspidersteveastrouk

Answer 7 years ago

I understand the output won't be more than 1.5 A. I'm asking if the 4A I put into the INPUTS of the lm317 would make it explode or get excessively hot.

The lm317 would probably slow down the 4A current right? But slowing it down from 4A to 1.5 or lower might cause it to be very hot or not functional. If so, is there a max input current? My reasoning may be wrong, which is why I'm asking.

Thanks anyway Steve!

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AndyGadgetDmxspider

Answer 7 years ago

 
You have a basic misunderstanding here - It's the OUTPUT current from the 317 which is important.  Whatever you connect to the output of the 317 will draw as much current as it needs (up to 1.5A). 
It sounds like you have a PSU CAPABLE of 4A, but it may only be required to supply a fraction of that.

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DmxspiderAndyGadget

Answer 7 years ago

OH! -comes to a complete understanding-

It makes sense now. I will go ahead and connect them together.

Thank you very much! Steve had the answer, Andy explained his answer!
Thanks again!

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AndyGadget

7 years ago

 
Keep an eye (or better still, a finger) on the 317 after you power the circuit up with the load connected.  If you're drawing more than a couple of hundred milliamps you'll need a heatsink on there to dissipate the heat.