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Low drop-out current sink with switch?

Discussion in 'Electronic Components' started by William P.N. Smith, Aug 31, 2003.

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  1. I'm looking for a constant current sink that'll control somewhere
    around one half to one amp or so with a low dropout voltage and a
    control pin.

    I'm currently awaiting some LM2941 LDO regulators, which (configured
    for current mode) look fairly ideal except the minimum voltage drop is
    going to be something like a couple of volts (1.275V for the reference
    voltage and a quarter to a half a volt for the device).

    Is there a way to do something like this using a MOSFET with (say) a
    constant gate voltage? My initial look at the IRLD024 makes it look
    like the current will vary considerably with temperature, and a bias
    resistor on the source pin gets me back up to the 1.5 volt range for a
    dropout, and then I still need an on/off control...

    Any thoughts?

    Thanks!
     
  2. mike

    mike Guest

    There used to be a thing called a sense fet. Brought out one fet cell
    on a separate source pin. You still need a negative power supply for
    all the biasing and sensing stuff, but it only has to carry a small
    fraction of the total current.
    mike

    --
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  3. Guest

    Use a low voltage rail-to-rail Op Amp with beyond-the-rail inputs to
    drive a NPN switching transistor. Sense the current with a tiny resistor
    in the emitter feed and configure this combination as a constant current
    source. A suitable Op Amp would be KM4101 (runs on a single 2.7V supply,
    60mA output capacity). Use the enable pin of the Op Amp to switch the
    current source on and off (KM4101 quiescent current 0.1mA).

    The 260MHz bandwidth of the KM4100/KM4101 is overkill, of course.

    Just an idea, I didn't try it!

    Martin.
     
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