Inductor for 34063 switching regulator

Discussion in 'General Electronics Chat' started by spinnaker, Oct 21, 2012.

  1. spinnaker

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  2. bountyhunter

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    You don't know the most important specs for the inductor: current rating and design frequency.
     
  3. ScottWang

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    absf likes this.
  4. takao21203

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    This circuit is actually based on said IC. Performing a long-time test.
    You can use the RF inductors, but only for some 10mA.
    And really depends on the value.

    It is a difference if you use a 12uH RF inductor or 220uH.
    12uH has much lower resistance. So they can be used for small PCBs.

    For 220uH, you rather need a larger pot core like in the photo.
    Consider the nominal max. current, and generously multiply that by factor 2 (also depends on the stepping ratio).

    If you choose a too low current rating, you can end up with pretty bad efficiency (and thus, heat developement). DC/DC circuits need some headroom for the coil if you want max. efficiency. This is due to various reasons such as magnetic saturation, and Ohm's DC resistance of the copper wire.
     
  5. spinnaker

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    It is just to power a pic so my current needs will be very minimal.

    My input voltage will be 8-13.5 vdc.

    And be fairly efficient since it is being powered off of a SLA battery which also powers a LED spotlight. So the more efficient the better.

    Any suggestions?
     
    Last edited: Oct 22, 2012
  6. THE_RB

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    I've used inductors that size up to a couple of hundred mA, it depends on their DC ohms, which unfortunately are not listed in the ebay advertising.

    My experience with that size inductor and 220uH is that the DC ohms would probably be under 3 ohms, so I would expect it to be good for 100mA or quite a bit more, definitely enough to run a PIC.

    Along with the DC ohms spec those type inductor should have a max DC current spec, because they have really fine wire they will "fuse" with too much current.

    Here's a link to a 5v buck converter that used a worse inductor (1500uH 8.7 ohms) that was perfectly ok to 100mA or so;
    http://www.romanblack.com/smps/a00.htm
     
  7. spinnaker

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    What size? The one I posted?

    Thanks for he link BTW.
     
  8. takao21203

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  9. THE_RB

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    There was a photo of it on the page I linked to, here's the photo;

    [​IMG]

    Yeah some brands will state a very low current rating for all the inductors in that size, but the truth is that the lower inductance values use less turns and thicker wire.

    Like I said I've had good experiences with 100mA + and no problems. Even with the 8.7 ohm inductor on my page at 100mA 8.7 ohms that's only 87mW heat in the inductor. With a 220uH inductor it's probably 3 ohms or less so 100-200mA should be no problem.

    At "running a PIC" type currents (10mA?) those few ohms in the RF style inductor won't really cost you much efficiency.
     
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