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Buck switcher chips

Discussion in 'Electronic Design' started by Phil Hobbs, Jul 19, 2013.

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  1. Phil Hobbs

    Phil Hobbs Guest

    So we've got the +-40V sorted out, thanks to all. The next bit to
    re-examine is the two buck regulators, both LM2594s, one for +5 and one
    for -15.

    The TI LM2594MX-ADJ is about $1.40 in 100s, and there are zillions in
    stock. The ONsemi clone, LM2594D, is only 64 cents, but it looks like
    Digikey is the only distributor with any stock, and they have less than
    one reel.

    I like the medium-old bipolar switchers, because their nice slow edges
    make me less worried about switching junk getting into my low level
    circuitry.

    Any idea why the ONsemi ones are both cheap and apparently unpopular?

    Any suggestions for buck chips that will handle at least 40V and 0.5 A?

    Cheers

    Phil Hobbs

    --
    Dr Philip C D Hobbs
    Principal Consultant
    ElectroOptical Innovations LLC
    Optics, Electro-optics, Photonics, Analog Electronics

    160 North State Road #203
    Briarcliff Manor NY 10510

    hobbs at electrooptical dot net
    http://electrooptical.net
     
  2. Phil Hobbs

    Phil Hobbs Guest

    I looked on the ONsemi site, and they're discontinuing the DIP package
    but not (so far) the SO8.

    The +5 load is relatively light--it's running a 3.3V LDO for a small ARM
    with a bit of external flash and sram, some optos, a display, and an
    FDTI chip. So maybe 200 mA.

    The -15 can be at least that, because there are beefy op amps driving
    series-terminated 50 ohm BNCs that somebody might decide to terminate in
    50 ohms. But no more than 250 mA.

    Cheers

    Phil Hobbs



    --
    Dr Philip C D Hobbs
    Principal Consultant
    ElectroOptical Innovations LLC
    Optics, Electro-optics, Photonics, Analog Electronics

    160 North State Road #203
    Briarcliff Manor NY 10510

    hobbs at electrooptical dot net
    http://electrooptical.net
     
  3. I tend to go the other way! Higher magnetics frequencies are easier to
    filter and are attentuated more by groundplanes. The fall in PSRR of the
    opamps gets compensated by the improvement in local filtering.

    Works best when signals are relatively slow I suppose, slower that the
    SMPS.
     
  4. Joerg

    Joerg Guest

    There's always the old MC34063, almost dates back to Methusaleh, which
    can be had for slightly above $0.10 in qties:

    http://www.st.com/web/en/resource/technical/document/datasheet/CD00001232.pdf

    The BD9876 is around $0.50, more efficient, but you'd have to see if ok
    for the inverter job:

    http://rohmfs.rohm.com/en/products/databook/datasheet/ic/power/switching_regulator/bd9876efj-e.pdf

    The others I have encountered are mostly over a Dollar. If you can
    stomach an external FET there may be some further penny-pinching
    possible in case the MC34063 is not to your liking.
     
  5. Joerg

    Joerg Guest

    The current sense only adds 200mV. The switch drop is a pain but you'll
    have that in almost almost all slow and old regulators.

    One way to find out would be to ask a TI app engineer :)
     
  6. josephkk

    josephkk Guest

    That is elegant to a cruel level.

    ?-))
     
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