collector voltage feedback.

Discussion in 'General Electronics Chat' started by hobbyist, Jul 18, 2009.

  1. hobbyist

    Thread Starter Distinguished Member

    Aug 10, 2008
    What are the benefits of collector voltage feedback, when it will decrease input impedance, unlike emitter resistor series current feedback that increases the input impedance?
    Can someone please tell me, cause I'm reading up on this, and not seeing the benefits of it with respect to current feedback,

  2. The Electrician

    AAC Fanatic!

    Oct 9, 2007
    Anytime you increase or decrease an input or output impedance, if you achieve a better match with the source or load impedance, you may get better power gain. That would be the motivation for changing an impedance with feedback.

    This feedback configuration you describe can be used with DC coupling to stabilize the bias of a bipolar transistor.
  3. millwood


    emitter feedback is typically preferred. However, when you increase the emitter resistance, you have to increase the collector resistance to maintain gain. That causes the transistor to run lean, and to have higher output impedance (if the output is taken from the collector). that may not be desirable at all times.
  4. alphacat

    Active Member

    Jun 6, 2009
    When you're talking about achieving a better impedance match,
    are you talking about having Rin>>Rs, Rout>>RL in the case of a transconductance amplifier for example?

    It just that I also learn about the term impedance matching in transmission lines course, so i was wondering which did you mean.

  5. DC_Kid

    Distinguished Member

    Feb 25, 2008
    possibly for current limiting?