Transistor HFE & data sheets

Discussion in 'General Electronics Chat' started by Steve1992, Oct 10, 2006.

  1. Steve1992

    Steve1992 Thread Starter Senior Member

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    With reference to 'HFE Classification' on pdf.

    There are 3 classes of BC548; postfix A,B,C.

    If my circuit had a base current was 150uA and collector current 40mA (common-emitter config.)
    HFE = 266.

    Would it matter if I chose BC548A, ..B or ..C transistor?


    Steve
     
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  2. Papabravo

    Papabravo AAC Fanatic!

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    Well of course it matters. Where you need to start is from the following two points.

    #1 - Never design a circuit which depends on a specific value of hFE
    #2 - Understand that the ranges represent plus and minus three sigma points on a normal distribution. This means that 99% of all transistors in the population will have an hFE inside the range. That leaves 1% with values that are either higher or lower.

    We live in a statistical world where a range of values is equivalent to giving a mean and a variance. The proper way to design a circuit is to be insensitive to the actual value of hFE, or to at least funtion correctly over a suitable range. If you don't know how to do that then you need to ask more questions.
     
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