Need "noise free" boost regulator

Discussion in 'The Projects Forum' started by Mikrogut, Jun 10, 2014.

  1. Mikrogut

    Thread Starter New Member

    Aug 30, 2013
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    Hi,

    I need a 5V/500mA boost regulator that can give me 5V from a 3.7V Li-Ion battery. Currently I am using the L6920 together with a 18uH inductor. The problem with the current solution is noise and ripple. I can hear a high frequently squealing from the inductor when the regulator is loaded. In addition there is +/-60mV ripple on the 5V output. I want a small ripple and I don't want to hear the conductor squealing.

    Any suggestions for a 5V/500mA boost regulator that I can use instead?
     
  2. Sensacell

    Well-Known Member

    Jun 19, 2012
    1,132
    267
    Find one with a higher switching frequency.

    1) You will not hear it

    2) the ripple frequency will be higher and easier to filter.
     
  3. alfacliff

    Well-Known Member

    Dec 13, 2013
    2,449
    428
    are you using a store bought inductor, or homemade? if homemade, or exposed windings, coat it in epoxy, that will stick the windings down and prevent vibrations. for the ripple, use a ceramic cap to filter out the ripple, using the shortest leads possible.
     
  4. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    5,805
    1,105
    If the squeal is due to inductor overload try using a bigger inductor core (higher current rating).
     
  5. Mikrogut

    Thread Starter New Member

    Aug 30, 2013
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  6. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    That is true. Also, Linear Tech has some specialty dc/dc controllers optimized for low noise. But relatively high output noise is a common characteristic of all boost converters. Consider a second inductor as part of an extra output filter stage.

    That's a good group of capacitor values, but as mentioned above capacitor type and placement have as much or more to do with performance than value. Also, pcb layout is critical. Follow the demo board if you can - they usually are optimized to make the part look as good as it can get. In particular, pay attention to any traces near (or under) the inductor.

    ak
     
  7. ronv

    AAC Fanatic!

    Nov 12, 2008
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    My 2 cents. I think your inductor is a little small and the current rating a little low. It may be saturating at high current. A little LC circuit or more capacitance at the output should fix the ripple. But for fun sign up for web bench (TI) and look at some of their designs. I just did one below for a couple bucks in parts and 1 mv ripple.
     
  8. crutschow

    Expert

    Mar 14, 2008
    13,052
    3,244
    An added LC filter at the output will also reduce (electrical) noise and ripple.
     
  9. Mikrogut

    Thread Starter New Member

    Aug 30, 2013
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    I only draw about 200mA@5V from this regulator, so I don't think I am overloading the regulator or inductor.
     
  10. Mikrogut

    Thread Starter New Member

    Aug 30, 2013
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    How about using TPS61230 or TPS61027 from TI? They work at a higher frequency and require smaller inductors. That might help me removing the hearable squealing from my current solution.

    I don't know how the 5V ripple would be, but it can't be much worse than now.
     
  11. Papabravo

    Expert

    Feb 24, 2006
    10,163
    1,796
    You don't think or you know for certain? In an SMPS it is not unusual for the inductor current to be much greater than the output current. Thin wire or the wrong kind of core material and the inductors could very easily saturate.
     
  12. THE_RB

    AAC Fanatic!

    Feb 11, 2008
    5,435
    1,305
    Agreed. Just use a bigger inductor.

    At a low average current of 200mA it's not going to be critical for DC ohms etc so there is no need to use such a small inductor.

    Larger inductor means less current ripple, and a larger output cap means less voltage ripple per load.
     
  13. Mikrogut

    Thread Starter New Member

    Aug 30, 2013
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    0
    Today I tried this conductor which I had lying around:
    www.digikey.com/product-detail/en/ELL-6RH100M/PCD1345CT-ND/295721

    The result was that the high frequency squealing disappeared. That was very good! The squealing was probably a result of a saturated inductor. The ripple is still high, but a bigger inductor and a LC filter will probably help.
     
    Last edited: Jun 16, 2014
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