How to interpret the hFE(beta) in a transistor datasheet?

Nabi, the most direct route is to simply measure hFE at the operating point you are contemplating.

Small signal current gain varies considerably from transistor to transistor. Circuit designers often employ negative feedback to limit a transistor's hFE so that mass-produced circuits will function more-or-less the same despite variability in transistor characteristics.

Chuck

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My data book shows it is over 100 up to 0.5 amp Ic.

Then falls to about 25 at 3 amp Ic.

This is at a fixed Vce of 2 volts.

More Vce will only improve the figure.

Vce sat is about 1.2 volts at 3 amp Ic with 300 mA Ib.

Simple.

........ Phil

The more "sophisticated" way would be to design the circuit such that hFE (aka bets) variations don't really make all that much difference. Like, design for the low value, but arrange the circuit (feedback, etc) so that using a higher-gain transistor will still give the same answer.

In other words, design it out. :-)

Good Luck! Rich

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The HFE changes with voltage and current. I would always allow an overhead of 50% on any design I made to be safe.