Full Saturation BJT

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

  1. robog33

    Thread Starter New Member

    Oct 13, 2008
    1
    0
    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?

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  2. hgmjr

    Moderator

    Jan 28, 2005
    9,030
    214
    Let us know how far have you been able to get on your own?

    hgmjr
     
  3. hitmen

    Active Member

    Sep 21, 2008
    159
    0
    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
    764
    56

    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
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