more on level shifter

Discussion in 'General Electronics Chat' started by tibbles, Nov 5, 2009.

  1. tibbles

    Thread Starter Active Member

    Jun 27, 2008
    249
    3
    i do quite a bit with automotive stuff ,so i thought the circuit http://forum.allaboutcircuits.com/attachment.php?attachmentid=13208&d=1257131549
    well worth saving.
    just a couple of points,the output componant will of course depend on the load,but why an fet in this case?.

    when on, i'm only getting 7 volts at the output on a simulator (a pretty basic one) even if i apply 12 volts to the gate. what am i doing wrong?

    im fairly new, so i hope my question isnt too crazy,although ive somehow become a senior member, (a reference to my age no doubt).
    thanks in advance
    dougal
     
  2. MikeML

    AAC Fanatic!

    Oct 2, 2009
    5,450
    1,066
    Because the existing NFet is being used as a source follower. Its source will always be more than one threshold voltage below the gate. If you want a fully-on or off FET switch, you will have to put the FET in a common-source configuration. Depending on if you need the driver to be inverting or not, that will determine if you need to use an NFet or PFet.
     
  3. tibbles

    Thread Starter Active Member

    Jun 27, 2008
    249
    3
    thanks Mike for your prompt response, i think ive got that.


    dougal
     
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