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What is a power follower ?

Discussion in 'Electronic Basics' started by little billy, Aug 4, 2004.

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  1. little billy

    little billy Guest

  2. A follower is an amplifier that provides current gain, but has a
    voltage gain of very nearly one. Power varies. This one is an
    integrated transistor operated as an emitter follower (that also
    includes short circuit current limit and over temperature cut off)
    with the LM317 acting as a constant current load (1.2 volts at its
    output loaded with a resistor so that it passes 1.2/r through the
    resistor, and only a tiny bit more than that at its input. So the
    pull down current is limited to this fixed current, and the pull up
    current is limited by the higher current limit of the integrated
    transistor. Just a beefy but protected emitter follower.
  3. little billy

    little billy Guest

    Hello again,

    I see, so "power follower" is "power emitter follower".
    R1 is a bit strange for an emitter follower, and no biasing
    for T as well , but I do see what you mean.

    Thanks. More questions coming up, as the documentation of the lm317
    is full of circuits which seem to be good to know.
  4. I suspect it is included as part of the input current limit if the
    LM195 goes into any protective shut down. This would not much apply
    to an ordinary transistor.
    Most emitter followers (except for push pull complementary designs
    like LM6121: )
    do not correct for temperature shift in the base emitter drop.
    You might also look up the data sheet for the LM195, to understand
    more of the function of the follower.
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