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Is the 4066 suitable for power switching?

Discussion in 'Electronic Design' started by galapogos, Nov 8, 2006.

  1. galapogos

    galapogos Guest

    Hi,
    I'm using a 4066 quad switch to turn on and off 2 devices, an
    oscillator and a smart card, both of which accept 3.3V. I'm wondering
    if the 4066 is capable of driving enough current, because my voltages
    seem to drop on the output side even though oscillators/smart cards
    don't really draw much power.

    I measured the various pins on the 4066. My control signals are 3.3V,
    and the inputs are also 3.3V, but the output to the osc is only
    2.9-3.0V while the output to the smart card is only ~2.8V. When I
    remove the smart card the output jumps back to 3.3V. What's wrong here?

    Thanks!
     
  2. Fred Bartoli

    Fred Bartoli Guest

    galapogos a écrit :
    RDSon.
    Read the datasheet.
    There are specialized power supply switches and the 4066 isn't one at all.
     
  3. AJ

    AJ Guest

    The 4066 has a series resistance which might be why your having problems.
    Maybe you could try some transistors on the output.

    Regards


    AJ
     
  4. Eeyore

    Eeyore Guest

    The transmission gates have an ON resistance you'll find in the data sheet.

    Graham
     
  5. galapogos

    galapogos Guest

    Thanks. I read the datasheet but no Ron was given for 3.3V. I guess I
    can extrapolate that from the 5V figures. Anyway, are there any generic
    switches that work for power switching? I don't expect anything more
    than 60mA.
     
  6. Tim Wescott

    Tim Wescott Guest

    If you're switching a 3.3V rail with a 3.3V signal and all grounds are
    common you can just use a PMOS FET. It's basically what you'd be
    getting from a specialized switch, and it's (probably) cheaper and
    (maybe) smaller.

    If you can stand a bit of drop (less than 0.2V) you could use a PNP
    transistor. Zetex has some low VCEsat devices in NPNs and may have them
    in PNPs as well -- but why not use a FET?

    You could also consider a 74ACT4066, or just a 74ACTxx buffer ('06?).
    These will have lower on resistances than a plain old 4066, and may be
    enough.

    --

    Tim Wescott
    Wescott Design Services
    http://www.wescottdesign.com

    Posting from Google? See http://cfaj.freeshell.org/google/

    "Applied Control Theory for Embedded Systems" came out in April.
    See details at http://www.wescottdesign.com/actfes/actfes.html
     
  7. colin

    colin Guest

    "Fred Bartoli"
    yep, but if uve only used one of the switches maybe putting them all in
    parallel might give you a bit more voltage.

    Colin =^.^=
     
  8. galapogos

    galapogos Guest

    Hi,

    I tried using a 2N930 NPN transistor with the collector wired to the
    oscillator ground, the emitter wired to ground, and the base wired to
    the control output signal from my MCU gpio pin, with a 1K series
    resistor. However, the io pin voltage seems to be ~3.15V no matter what
    I drive it with my application, and the base voltage is ~0.7V. VCE is
    always close to 0V, which means the oscillator is always getting full
    Vcc. What am I doing wrong here?
     
  9. classic part for this is something like the FDG6324 or FDG6323

    David
     
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