lm2576t troubles

Discussion in 'General Electronics Chat' started by chunkmartinez, Dec 21, 2012.

  1. chunkmartinez

    Thread Starter Senior Member

    Jan 6, 2007
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    Has anyone used this voltage regulator? I'm trying to use it and a 9v batteryas a ortable cell-phone charger. Well, the light on the cellphone comes on but the cellphone dosn't charge. I am guessing it cannot source enough current? Maybe the inductor I used dosn't allow enough current? The current on my charger says 400ma so this is what I'm assuming I need to be able to supply. Well, that voltage regulator allows I believe 3A which is more then enough.

    I just cant figureout the prob. I have measured the current inline and I see very little current, much less then 400ma...Any ideas heres the schematic:

    http://www.ti.com/lit/ds/symlink/lm2576.pdf
     
  2. GopherT

    AAC Fanatic!

    Nov 23, 2012
    6,058
    3,820
    Measure the DC resistance of your inductor. That may be limiting you current.
     
  3. chunkmartinez

    Thread Starter Senior Member

    Jan 6, 2007
    180
    1
    I got about .5 ohms from it..
     
  4. chunkmartinez

    Thread Starter Senior Member

    Jan 6, 2007
    180
    1
    Okay so today I simply swapped the 9v with 5 series AAs because I figured the 9v couldn't supply 400ma long enough before dying. Do 9v really have that loe of an AH? I figured they did after looking at a comparison chart, a AA holds much more! Now it kindof sucks having to use 5 AA to only utilize the capacity of just one. I am going to look into voltage boosters or doublers.
     
  5. bountyhunter

    Well-Known Member

    Sep 7, 2009
    2,498
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    9V batteries have a high internal resistance which probably can't supply the peak currents needed.

    You also need a large value, low ESR capacitor at the input pin of the 2576. Bigger the better.
     
  6. chunkmartinez

    Thread Starter Senior Member

    Jan 6, 2007
    180
    1
    Yeah I used low esr caps...but I didn't know that about 9vs. Thanks..
     
  7. crutschow

    Expert

    Mar 14, 2008
    13,016
    3,235
    9V batteries are designed for low current applications (tens of milliamps). AAs or AAA's are much better for higher currents. But note that if you use fewer batteries and boost the voltage, the battery current will increase proportionally, so the battery life will be shorter. There's no free lunch.
     
  8. chunkmartinez

    Thread Starter Senior Member

    Jan 6, 2007
    180
    1
    Yea I realized all this while experimenting...too bad.
     
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