about MOSFET current mirror

Discussion in 'General Electronics Chat' started by CantataAndAria, Dec 10, 2014.

  1. CantataAndAria

    Thread Starter New Member

    Nov 14, 2014
    11
    0
    1. The N-channel MOSFET given in datasheet is like this:
    1.png

    but the MOSFET N-channel current mirror in simulation software is like this:
    2.jpg

    I'm confused about the direction of the arrows and the G/D/S of pins. Can anyone explain briefly?


    2. I have three MOSFETs of the same model. I built a small MOSFET N-channel current mirror. Assume the connection is correct (I'm not sure), the output current tested by using different pairs are very different.

    LEFT RIGHT CURRENT (mA)
    MOSEFET1 MOSFET2 119
    MOSEFET1 MOSEFET3 13
    MOSEFET2 MOSEFET1 0
    MOSEFET2 MOSEFET3 0
    MOSEFET3 MOSEFET2 76
    MOSEFET3 MOSEFET1 3.9
    Is this probably because one of the MOSEFETs is broken???
     
  2. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    5,809
    1,105
    The symbol depends on whether an enhancement mode or depletion mode MOSFET is shown. See, for example,
    http://en.wikipedia.org/wiki/MOSFET
    Which model MOSFET were you using?
    Even different samples of the same model will probably have different gate-source threshold voltages, which may skew your current-mirror results.
     
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