Inductor question

Discussion in 'The Projects Forum' started by dnalevy, Apr 24, 2013.

  1. dnalevy

    Thread Starter New Member

    Apr 24, 2013
    2
    0
    Hi there everyone!
    I'm new to this site and your help would be very much appreciated.
    I'm trying to build the following circuit:

    [​IMG]

    The only thing I'm unsure about is the inductor. The data sheet says 'use a 2.2uH inductor for 600kHZ operation'. Does that mean if I leave the max1708 as is without changing the frequency any 2.2uH inductor will work?

    I was hoping to use this inductor because of the size but it mentions 100kHZ which made me unsure.
    http://www.digikey.co.uk/product-detail/en/74437346022/732-3372-1-ND/2790967

    Pardon my ignorance I'm a little rusty, trying to get my bearings again.

    Thanks!
     
  2. aws505

    Member

    Mar 11, 2013
    59
    7
    What DigiKey is mentioning is only the frequency at which they tested the inductor. Remember, inductance can change with frequency. DigiKey has, nicely, tested that inductor with an inductance meter, but they only did the measurement at 100 kHz. The inductance is likely quite constant with frequency; Usually you need to start worrying about inductance changes above 100's of MHz, or if you have a really funny-looking inductor.

    Your choice should be fine for 600kHz operation.
     
  3. crutschow

    Expert

    Mar 14, 2008
    13,042
    3,243
    It can't just be "any" 2.2μH inductor. The inductor also needs to be rated for the maximum inductor ripple current, which is greater than the maximum output current you will be using.
     
  4. dnalevy

    Thread Starter New Member

    Apr 24, 2013
    2
    0
    Thank you aws505 and crutschow thanks the current rating is 6.5A which is way over the max current I hope to use.
     
  5. WBahn

    Moderator

    Mar 31, 2012
    17,768
    4,804
    In general you can't use just "any" inductor because of parasitics (among other things such as max voltage and max current limits). But at 600kHz I don't think you will have any problems.
     
  6. takao21203

    Distinguished Member

    Apr 28, 2012
    3,577
    463
    Normally 600 KHz is no problem for 2.2uH inductors.

    Larger inductors can have considerable loss already at that frequency.

    Some materials are only good for about 100 KHz.

    As soon as the magnetic core goes into saturation area, loss will increase a lot.

    It is not just the max. specified nominal current, which you supposed to be could max out 100% to the given value.

    You can only drive with substantial smaller current, and at some point saturation begins, or partial saturation during spikes.

    6.5A nominal value should be fine for your purpose as well these types of inductors should have specification for 600 KHz at least at this value of 2.2uH
     
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