hybrid pi model confusion

Discussion in 'General Electronics Chat' started by acelectr, Mar 19, 2011.

  1. acelectr

    Thread Starter Member

    Aug 28, 2010
    Hi, till now when worked on any convertion of an npn bjt to a pi or T model I didn't have any troubles but now I'm in a situation that I need to do this same process for a pnp BJT which I really couldn't do:( . What changes occur for the pi model for a pnp. at an npn bjt the emitter current comes from the base and in a pnp the emitter current goes in to the base so ....

    appriciate any help:rolleyes:
  2. steveb

    Senior Member

    Jul 3, 2008
    Well, the DC currents and voltages will be negative with a PNP device. So, any DC equivalent circuit needs to account for the polarity changes.

    But, the AC model can be the same for both PNP and NPN devices. This works because the AC models are linearized models working at a DC operating point.