Audio noise when charging phone off step down controller

Discussion in 'General Electronics Chat' started by trader007, Sep 13, 2013.

  1. trader007

    Thread Starter Active Member

    Feb 27, 2010
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    i have a few of these- http://www.ebay.com/itm/Hot-LM2596-...248?pt=LH_DefaultDomain_0&hash=item1c367bf788

    [​IMG]

    They work great to hold a specific voltage, however they seem to have a noisy output. When I plug my phone in to charge, I get noise out the headphone jack.

    This is even when the step-down controller is running off batteries! I also have touchscreen issues when the charger is charging the batteries, and the phone is plugged in, but that is not much of a worry (happens a lot with android devices).

    I would just like to be able to charge my phone off these batteries (14v lithium pack) without causing a noisy audio output... What would be the easiest/cheapest way to do it?

    thanks!
     
  2. bountyhunter

    Well-Known Member

    Sep 7, 2009
    2,498
    507
    Change to a linear regulator. All switchers put out a ton of EMI like a little radio station. They also have voltage ripple on their outputs that creates hum and noise. That is a byproduct of using a switcher.
     
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  3. trader007

    Thread Starter Active Member

    Feb 27, 2010
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    Sounds good. I bet I even have one in my clusterfrick of a workshop
     
  4. trader007

    Thread Starter Active Member

    Feb 27, 2010
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    well... tonight i added l-pads and capacitors to my tweeters, and the noise went away. not sure if its the capacitors or a coincidence, but its charging the phone without any noise for about an hour now. working great!!

    I think i will still find a linear stepdown fet, just to keep things clean.
     
  5. trader007

    Thread Starter Active Member

    Feb 27, 2010
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    Well the noise is back of course, so I got a few (dozens) of LM323T's to replace my switching step down controllers.

    Apparently I mis-judged the thermal output though, as even with a heatsink it only takes about a minute to become too hot to touch.

    ~15v in going to 5v 1a out and its hot like soldering iron. Not going to work!! Oh well, I think I will just deal with the subtle noise.
     
  6. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
    4,769
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    or just use a lower input voltage
     
  7. bountyhunter

    Well-Known Member

    Sep 7, 2009
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    You could try a series L-C filter in line with the power lead going to the phone. That will knock it out if the problem is conducted EMI. If it is radiated EMI, that's harder to block.
     
  8. trader007

    Thread Starter Active Member

    Feb 27, 2010
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    Best I can tell it is conducted. I will try that, thank you.

    This is a portable radio, so using a linear controller wasn't ideal anyway as the switching ones have much greater efficiency

    Is there an easy way to tell what size components I need for the filter, if my power source is 5v @ 3a max? Sorry if its a dumb question, I will try learning it from google in the meantime.
     
  9. shteii01

    AAC Fanatic!

    Feb 19, 2010
    3,386
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    I guess pick a frequency you want to block. Once you have the frequency, you plug it into formula to figure out the L and C values.
     
  10. trader007

    Thread Starter Active Member

    Feb 27, 2010
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    well it sounds like "eeeeeeeee burp burp burp eeeeeeeee" so i suppose thats about 12khz? ;) I will play around and see what I can come up with. Need some coils first, I have none.

    really though, its hardly a worry. The noise is so little that unless youre right next to the speakers you can't hear it.
     
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