Full Saturation BJT

Discussion in 'Homework Help' started by robog33, Oct 13, 2008.

  1. robog33

    Thread Starter New Member

    Oct 13, 2008
    I have a BJT problem that requires me to find the Vin and the resulting Vout(Ve). Given values are the Vp=5V, Rc=1kΩ, Rb=1kΩ, Rout=1k(located at the emitter), β=100. At full saturation, is Vce always 0.2V?

  2. hgmjr


    Jan 28, 2005
    Let us know how far have you been able to get on your own?

  3. hitmen

    Active Member

    Sep 21, 2008
    Let me try. My answers WILL be wrong cos I am just studying this too.

    Ic = Vp-Vcesat / 1000 = 4.8mA

    βIb = Ic

    so Ib = 48μA

    Vin - Vbesat /1000 = Ib

    Vin = 0.248V

    I dunno how to find Vout. Neither do I know the purpose of the 1000Ω at the emitter. I also need help too:confused:
  4. hobbyist

    Distinguished Member

    Aug 10, 2008

    I'm not sure myself, but here is what I came up with:

    VP=Vin where the two circles may be used to denote a connection.

    so if VP=Vin
    and if Vce sat. =0.2V.
    then Ic=[(VP-Vce(sat.)) / (RC+RE)] where Ic will flow through both resistors and Q1 to ground as it is a series circuit.
    IB would be (Ic / Beta)
    and Vout would be [(Ic+Ib) X RE] where the combo of both Ic and Ib flow through RE.

    I believe the RE at the emitter is for bias and temp. stability, as well as if the output is coupled through a capacitor then RE will allow a negative going signal to be produces as well as a positive signal. Without RE then the only signal output would be positive after a 0.7v. drop due to the Vbe, which would give a distorted output.

    As I said I'm only guessing at this solution.

    Nope my guess is wrong too.
    Because RE and RC have circles also.....

    Somebody can tell us how to do it.
    Last edited: Oct 18, 2008