Increasing sink current?

Discussion in 'General Electronics Chat' started by Razor Concepts, Apr 22, 2009.

  1. Razor Concepts

    Thread Starter Active Member

    Oct 7, 2008
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    I have a IC that can sink up to 38ma. I would like to drive higher currents but was wondering how i could do this. Usually I'm accustomed to working with things that source current, so using a darlington array would be standard. But I am unsure of how to do this with sinking current. Thanks
     
  2. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    If darlington array has seperate emitters, use as emitter followers; or use a PNP driven by a NPN transistor
     
  3. Wendy

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    Mar 24, 2008
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    A common use for current sinks is electronic loads for power supplies. I'm thinking of going with this...

    [​IMG]
     
  4. Ron H

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    Apr 14, 2005
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    If you ground the emitter of an NPN Darlington (or a normal NPN), and drive the base with a current-limited voltage, the collector will sink current.
     
  5. Razor Concepts

    Thread Starter Active Member

    Oct 7, 2008
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    I don't understand - the chip can only sink current so how does it drive the base with a current limited voltage?
     
  6. Wendy

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    Mar 24, 2008
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    Has to do with a transistor being a current controlled device and beta. Ic=ß Ib

    I prefer using the emitter resistor myself, with a controlled base voltage.
     
  7. Ron H

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    If your output can only sink current, you can make it possible to source current for the base of the Darlington (or plain NPN) by adding a pullup resistor to +V.

    See attachment.

    Note that if your circuit is analog, this won't work.
     
  8. Razor Concepts

    Thread Starter Active Member

    Oct 7, 2008
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    Thank you, now I understand. I think I'll use a ULN2003A Darlington. Is there a "standard" value pull-up I should use to test things out? Thanks.
     
  9. Ron H

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    Apr 14, 2005
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    It depends on what your load current is.

    What is your driving device - the one that can sink 38mA?
     
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