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why open drain vs push pull?

Discussion in 'General Electronics Discussion' started by docb, May 5, 2016.

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  1. docb

    docb

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    Feb 11, 2010
    Driving a FET/BJT with the logic output of an IC.
    There are ICs with "open drain" outs, or "push pull" outs.

    If I use a pull-up with the open drain, is there some benefit of that over the push pull choice, or vice versa?
     
  2. Alec_t

    Alec_t

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    Jul 7, 2015
    Open drain allows easy OR-ing of two driver signals if required, but needs a pull-up resistor. Push-pull provides a low impedance path to both rails.
     
    hevans1944 likes this.
  3. docb

    docb

    131
    2
    Feb 11, 2010
    Thanks! Sounds like just to drive a single FET, push pull is the better choice.
     
  4. Alec_t

    Alec_t

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    Jul 7, 2015
    If you're turning the FET on only occasionally, the open drain plus pull-up resistor would be fine. It's when the FET requires high-speed switching that the push-pull driver comes into its own, to avoid the FET overheating as a result of it spending too long in the 'only-half-turned-on' state.
     
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