BJT emitter follower amplifier power dissipation

Discussion in 'Homework Help' started by spassig, Apr 7, 2011.

  1. spassig

    Thread Starter New Member

    Apr 7, 2011

    I am completely stuck trying to understand the power dissipation of a BJT emitter follower class-A amplifier.

    Take for example the circuit on page 91 on The Art of Electronics - picture in attachment.

    I understand the role of Q1 and the current source, but I don't understand why it is said that, with no signal, the transistor dissipates 55W and the emitter resistor 110W?

    The loudspeaker, being 9V RMS at 8 ohm, needs about 1.6A of current peak. So this is the quiescent current the transistor needs to drop as power, is that right?

    So how can 55W and 110W come out?

  2. spassig

    Thread Starter New Member

    Apr 7, 2011
    ouch...not sure what I was thinking this morning when I asked this :)

    I just thought again about it and its solution is really trivial. sorry for asking here.
  3. Audioguru

    AAC Fanatic!

    Dec 20, 2007
    The class-A amplifier can heat your entire neighbourhood.