Why two the same MOSFET in a circuit?

Discussion in 'General Electronics Chat' started by booboo, Jun 10, 2016.

  1. booboo

    Thread Starter Member

    Apr 25, 2015
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    Hey guys
    What's this circuit? look:

    [​IMG]

    Why the designer has used two the same MOSFET with the same resistor? I mean coundn't the designer design the above circuit like this?:

    [​IMG]
     
  2. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    @booboo
    In your second picture, the output is high when input is low.

    In the first picture, the output is high when the input is high.
     
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  3. DickCappels

    Moderator

    Aug 21, 2008
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    Of course the noninverting amplifier probably could have been made with a single common base circuit
     
  4. booboo

    Thread Starter Member

    Apr 25, 2015
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    Ah-ha! then it is a logic level-shifter. 5v to 3v3
     
  5. GopherT

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    Nov 23, 2012
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    I guess it could be but, 5V in to 3V out. But, as drawn and not knowing exactly what the rest of the circuit does, I would say that
    - one is an inverting buffer (bottom),
    - one is a non-inverting buffer (top).
     
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  6. jpanhalt

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    Jan 18, 2008
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  7. GopherT

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    Nov 23, 2012
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    I never seem to have a need for bi-direction level shifter. One direction has always been enough. It is an interesting metal challenge but in practice, an output drives an input. The output rarely switches to become an input and input becomes an output to necessitate a bi-directional level shifter.
     
  8. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    How about in an I2C bus? Clearly, Philips and Sparkfun felt there was a need. And a bidirectional bus can be use one-way too.

    John
     
  9. GopherT

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    Nov 23, 2012
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    If SparkFun is the seller, then the application will likely be some older/cheap/through-hole device communicating with an RPi.
     
  10. HW-nut

    Member

    May 12, 2016
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    The circuit may have been implemented for level translation.
     
  11. Techno Tronix

    Member

    Jan 10, 2015
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    Two MOSFET are used to block the voltages in both direction by allowing by directional current flow.
     
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