Emitter Follower

Discussion in 'General Electronics Chat' started by vindicate, Aug 27, 2009.

  1. vindicate

    Thread Starter Active Member

    Jul 9, 2009
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    0
    Is an emitter follower usually used with an AC source? I was doing some reading on it, and on most of the examples the base was AC. I can't really see it being that useful with a DC input.
     
  2. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    An emitter follower is used with an AC input riding on a DC bias voltage or with a DC input. It has no voltage gain and has a high input impedance and a fairly low output impedance. Opamps usually have emitter-follower inputs.
     
  3. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
    This is an alternate use for an emitter follower...

    [​IMG]

    It really depends on your imagination, it has some very useful characteristics.
     
  4. rjenkins

    AAC Fanatic!

    Nov 6, 2005
    1,015
    69
    One common application of an emitter follower with 'DC' is the output of a voltage regulator.

    Look at the internal diagram of a 7805 regulator, the output device is an emitter follower. (That's why they are not 'low dropout', the input voltage has to be high enough above the output to maintain the base drive).

    (Yes, PSUs have many possible configurations but the 78xx series are something most electronics enthusiasts are familiar with).
     
  5. russ_hensel

    Well-Known Member

    Jan 11, 2009
    818
    47
    In the long run every voltage is varying.
     
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