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Step-down switching regulator advice ?

Discussion in 'Electronic Design' started by Eeyore, Nov 10, 2007.

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  1. Eeyore

    Eeyore Guest

    I need a popular (easily available), low cost step-down switching regulator
    suitable for an input voltage of up to ~ 18V that will deliver ~ 1A @11V with
    Vin ideally as low as 11.25V.

    What would you recommend ? I'm not at all familiar with the offerings here.

  2. Guest
  3. mpm

    mpm Guest

    LM2575's switchers are pretty popular.
    Second sourced by ON Semi, and possibly others.

    Not sure about the 0.25V drop though.
    And you'd need the adjustable one - requires 2 external programming
  4. Eeyore

    Eeyore Guest

    Pricy ! That's around $10.

    Maybe I wasn't clear. I don't need a module, just a controller chip.

  5. Eeyore

    Eeyore Guest

    OK, got the data.

    An adjustable one is just fine.

    The low voltage drop is important to me. I suppose an alternative might be a
    buck-boost circuit. This would actually be even better suited to my needs. In which
    case my spec would be 1A @ 12.6V output with 11-18V in.

  6. Guest

    Keep waiting, the US dollar has a lot more sinking to do.
  7. Let's try electronics design with Google.

    In a panel at the right of your post in Google Groups
    is a "related pages" panel, where I see National
    Semi's LM2587 is recommended. Two clicks gets us to where we
    see that a simple flyback-transformer converter might
    work. In a panel to the right we see NSC's WEBENCH®
    tool to test the thought. OK, we enter 10 to 20V in,
    12.6V out, 1.5A max, and press START YOUR DESIGN.

    Oops, they want me to log on. Sigh. OK, press START
    again, and whammo, there it is -- our design, pretty
    routine, except a custom transformer is called out.
    But it's an easy one, with Ns/Np = 0.78, Lp = 23.4uH,
    and Lell no more than 0.47uH, or less than 2% of Lp,
    which is pretty easy to wind. They specify Rp under
    35 milliohms, which should help pin down the bobbin's
    winding area, and a ferrite-core size. They say the
    LM2587 will dissipate 3.5 watts, so we'll need a heat
    sink clip on the TO-220 tab.

    Hmm, DigiKey wants $8.32 just for an LM2587 TO-220-5
    IC. Maybe the $10 TI module isn't so bad after all.
  8. Fred Bartoli

    Fred Bartoli Guest

    Winfield Hill a écrit :
    Hmmm, maybe it's time to plan for a new chapter in AOE that'll teach
    back of the envelop mouse dragging and clicking...
    Then you can include there some nice lists of jellybean URLs for design
  9. Joerg

    Joerg Guest

    Every time I tried that I got a message that my design was not possible.
    All are in mass production now ...

    3.5W at 11W out? Ouch.

    Double-Ouch. I usually do SEPICs with the LM3478. About a buck in
    quantities and that external FET ain't expensive either. If it has to be
    dirt cheap I'll use a Schmitt inverter. And it usually has to be dirt cheap.

    It's like TV dinners. Either they are bland or expensive. When you whip
    up your own from scratch it costs less and tastes better.
  10. Joerg

    Joerg Guest

    Which then quit working during the first year of print...

    But you brought up a good point. Some links could be useful for younger
    engineers, especially to university sites that remain intact like this one:
  11. On Sun, 11 Nov 2007 17:07:18 GMT, in Joerg

    snip thinking guy's stuff

    I've never ever had a TV dinner

    this is quite a nice site

  12. Joerg

    Joerg Guest

    Same here. Even on lengthy biz trips where they rented me an apartment I
    cooked my meals. The farthest I went with pre-prepped stuff was a
    take-and-bake pizza.

    We use all our left-overs, trying never to throw food away.
  13. My best ever work trip, as a video guy, was in Kuala Lumpar, in the
    hilton for a month (Shyte), within 5 minutes walk, 35C, 95% RH, there
    where about 20 stalls of local food, 100K Scoville units and more, a
    full meal + beers for the price of a coke in the Hilton.

    I'm more into flavour these days than WMD


  14. Waist mangling deserts? ;-)

    Service to my country? Been there, Done that, and I've got my DD214 to
    prove it.
    Member of DAV #85.

    Michael A. Terrell
    Central Florida
  15. Eeyore

    Eeyore Guest

    Likewise. Very handy indeed.

  16. When the fet switches off, the drain shoots posive.
    That is the non-dot side of the primary.
    So the non-dot side of the secondary also shoots positive,
    opening the diode and charging the cap.
    You could of course change BOTH winding connections to get the same effect :)
  17. Sheesh, so obvious, thanks

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