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"A device will draw only as much current as it needs"

JonathanAnon

Mar 22, 2012
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I've heard this statement before on different sites.. But is it always true?

I'm trying to build a variable voltage adapter using an LM317T, and I can vary the voltage by using a potential divider at the output side, but there is no indication of the current, except that it can handle up to 1.5A (with a heatsink in place)..

Does this mean that if I set up my voltage for 19V, and hook it up to a 19V 2000mA load, the load will draw only the 2000mA that it needs and no more... And any 19V load that requires less than 2000mA should also work in this configuration?
 

john monks

Mar 9, 2012
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I think you mean 1500ma @ 19 volts. Without a circuit to follow I believe you are building a voltage source. So your circuit should supply 19 volts regardless of any current from 0 to 1500ma.
 

CocaCola

Apr 7, 2012
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But is it always true?

Until it's not true :)

I'm trying to build a variable voltage adapter using an LM317T, and I can vary the voltage by using a potential divider at the output side, but there is no indication of the current, except that it can handle up to 1.5A (with a heatsink in place)..

Does this mean that if I set up my voltage for 19V, and hook it up to a 19V 2000mA load, the load will draw only the 2000mA that it needs and no more... And any 19V load that requires less than 2000mA should also work in this configuration?

You can't get 2 amps out of the LM317 as you stated in the first paragraph it's only rated at 1.5 amps...
 

JonathanAnon

Mar 22, 2012
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0186-facepalm-30px-thumb-40x40-19845-thumb-30x30-19995.png


Yeah sorry.. I just picked that arbitrary number cos it's the highest current setting on any of the adapters that I have here..

I'll need a regulator that will handle a bigger current.
 

JonathanAnon

Mar 22, 2012
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That's the one I was trying to think of.. That guy Dave from the EEVBlog mentioned it..

 
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