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  1. #1
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    how to calculate ib of PNP

    hello guys,
    i would be thankful if you help me to find how to calculate ib of this PNP ??Click image for larger version. 

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  2. #2
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    Re: how to calculate ib of PNP

    Hi,

    hard to say without values. I guess 300 uA.

    No - joke aside.

    do you really want us to go give you a mathematical solution for all cases you can think of?
    * DC, what range?
    * AC, what frequency, amplitude
    * What values of the parts?

    ****
    some approches for DC cases: (for DC cases you may omit C1)
    * when V_IN is about 5V7 --> no current flow through D1, R2, R1 --> Ib is about zero.

    * when V_IN < (5V7 - D1_forward_voltage) ... (= when D1 becomes conductive) calculate: V_R1 = (5V7 - V_in - V_d1) * R1 / (R1 + R2)
    * now you have some new cases:
    .. * when V_R1 < V_BE_th: then ib is about zero
    .. * When V_R1 > V_BE_th: then consider V_R1 is about V_BE. Calculate I_R1. calculate anew I_R2, the difference between both is Ib.

    It all depends a lot on device types, temperature and so on.

    ****
    Why don´t you do just an LtSpice simulation?

    Klaus
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  3. #3
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    Re: how to calculate ib of PNP

    hello klaus,
    sorry for the messing informations, for Vin it is varies from 0v to 2,5v and for R1=3320ohm and R2=510ohm, thank you for your answer,



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  4. #4
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    Re: how to calculate ib of PNP

    thank you for your answer, about I_R2 is it equal to ((5V7-V_in-v_d1)*R2/R1+R2)/R2??
    Last edited by tronicman; 13th December 2019 at 15:48.



  5. #5
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    Re: how to calculate ib of PNP

    Hi

    thank you for your answer, about I_R2 is it equal to ((5V7-V_in-v_d1)*R2/R1+R2)/R2??
    you missed the brackets:
    ((5V7-V_in-v_d1)*R2/(R1+R2))/R2
    then you may simplify it:
    --> ((5V7-V_in-v_d1)*R2/(R1+R2))/R2
    --> (5V7-V_in-v_d1)/(R1+R2)
    (simple Ohm´s law: I = V / R)

    Klaus
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