Transistor HFE & data sheets

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Steve1992

Joined Apr 7, 2006
100
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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Papabravo

Joined Feb 24, 2006
12,302
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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