bidirectional level shifter

Discussion in 'The Projects Forum' started by mayank rob, May 28, 2014.

  1. mayank rob

    Thread Starter New Member

    Sep 18, 2012
    17
    0
    [​IMG]

    hello there
    I am trying to implement this bidirectional level shifter.
    I am using it on communication line of controller.
    the problem i am facing is that instead of 5v signal I am getting only 3.4V signal.
    I have checked all the other voltage levels and they are perfectly fine.
    Even 5V is proper.
    I am using BSN20 n channel mosfet,10k resistors,

    Thanks you anyway.
     
  2. alexfreed

    Member

    Oct 8, 2012
    72
    10
    Make sure drain is connected to the 5V side, not the source. Otherwise the internal diode will conduct when it shouldn't.
     
  3. mayank rob

    Thread Starter New Member

    Sep 18, 2012
    17
    0
    Thank you for reply
    Even my initial thought was that....but i checked for it and it isnt the case.
    I checked it thoroughly....connection polarity and even voltage supplies.
     
  4. AnalogKid

    Distinguished Member

    Aug 1, 2013
    4,538
    1,251
    What is the amplitude of the 3.3V signal when you are getting 3.4V on the 5V side?

    ak
     
  5. embpic

    Member

    May 29, 2013
    187
    3
    there so many chips as 74act125 which could give parallel trannsceiver lines.
     
  6. AnalogKid

    Distinguished Member

    Aug 1, 2013
    4,538
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    Not really. The 74ACT125 has unidirectional drivers with tri-state enables. That means that with two of them connected back-to-back, you need an external direction signal. The OP wants a circuit that works both ways automatically with no steering logic or direction signal.

    ak
     
  7. ronv

    AAC Fanatic!

    Nov 12, 2008
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    What is the state of your signals. In other words are they driven high and low or only driven when their output are low and then tri-stated?
     
  8. ronv

    AAC Fanatic!

    Nov 12, 2008
    3,290
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    Try this:
    The diodes in series with the signals are just to simulate the tri-state of your signals. D4 is there because the 7002 may still be on a little with 1.5v gate to source. If it isn't the low level on the 3.3 volt side may not go all the way to ground, but be a diode drop (internal diode) from ground.
     
    absf likes this.
  9. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    absf likes this.
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