Voltage Divider Bias circuit usage?

Discussion in 'Homework Help' started by Petrucciowns, Jul 7, 2009.

  1. Petrucciowns

    Thread Starter Active Member

    Jun 14, 2009
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    Can anyone give me an example of what a Voltage Divider Bias circuit would be used for. All I can find is theory, but not an example of its operation.

    Thanks.
     
  2. t_n_k

    AAC Fanatic!

    Mar 6, 2009
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  3. beenthere

    Retired Moderator

    Apr 20, 2004
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    Focus divider for electromagnetic lens focusing in TV CRT.
     
  4. hobbyist

    Distinguished Member

    Aug 10, 2008
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    Example: of it's operation..

    VCC=10 V.
    Rload = 10K ohms.
    Zin = > 2K ohms.
    Av. = 10
    RB1 is the voltage divider resistor from ground to the base of the transistor.
    RB2 is the resistor from supply to base, to form a "voltage divider"

    Make RC 1/10 Rload = 1Kohms
    make RE = 100 ohms. Av. = RC / RE
    VC = 5 V.
    IC = VC / RC = 5 / 1000 = 5mA.
    5mA X RE = VRE = 0.5V.
    VBE = 0.7V.
    VBE + VRE = VRB1
    0.7 + 0.5 = 1.2V. = VRB1

    Make RB1 = 2K ohms to satisfy Zin parameter.

    ID = divider current = VRB1 / RB1 = 1.2V / 2K = 600 uA.

    RB2 = (VCC - VRB1) / ID
    (10 - 1.2) / 600 uA. = 14.7K ohms.

    make it 15K ohms.

    So RB1 and RB2 form the voltage divider to provide a base voltage of 1.2V.
    so that in turn can cause a emitter voltage of 0.5V. wich ultimately determines the amount of collector current that willk flow through the transistor.

    Now some checking.

    VCC X RB1 / (RB1 + RB2) = 1.17V. = voltage at the base.
    1.17V. - 0.7 V. = 0.476V. at the emitter.
    so 0.467V / 100 = 4.7mA of collector current, assuming emitter asnd collector current are the same in the calculations.

    Hope this is a good example to put with the theories you learned.

    I keep rereading your post and think maybe this isn't the example your looking for afterall. I don't know.
     
    Last edited: Jul 7, 2009
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