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How to choose Hfe in common emmiter amplifier circuit

  1. Jul 21, 2013 #1
    I am using a transister model BC107bp in multisim, and i found that its min Hfe is 40 and max Hfe is 450. If I want to construct an amplifier circuit, i should choose the min or average? I found most of the datasheet show the hfe of collector current at 2m A (min 200 - max 450), but if my collector current is 1mA, should i choose the min Hfe which is 40? Any suggestion?
     
    Last edited: Jul 21, 2013
  2. jcsd
  3. Jul 21, 2013 #2

    Baluncore

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    Science Advisor

    It depends on the amplifier configuration.
    If it is a common emitter amplifier then high frequency response will be hurt by a high Hfe.
    If it is a common base amp it will not be sensitive to Hfe variation.
    If it is common collector, (emitter follower), then input impedance will be affected by Hfe variation.

    Design engineering requires that you perform a worst case analysis where all parameters vary. A student or hobbyist should start modelling with average values, then test some parameter extremes as a learning exercise. Explaining the changes observed with parameter changes will be highly educational.
     
  4. Jul 21, 2013 #3
    For the Ic = 1mA you shoudl choose hfe = 200.
     
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