Transistor HFE & data sheets

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

  1. Steve1992

    Steve1992 Thread Starter Senior Member

    Apr 7, 2006
    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?

  2. Papabravo

    Papabravo AAC Fanatic!

    Feb 24, 2006
    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.