Bipolar Junction Transistors - How does one read the datasheet?

1. Dec 20, 2012

d.arbitman

In particular, I am looking at a datasheet of a PNP BJT:
http://www.fairchildsemi.com/ds/2N/2N3906.pdf

I noticed that in the ON CHARACTERISTICS sub-heading, there were multiple $h_{FE}$ values. I'm wondering how I could extract any meaningful information from that since the most common $h_{FE}$ value is ~100. I also don't understand why the test $V_{CE}$ value is only -1.0V; shouldn't there be a wider range of applicable voltage drops from collector to emitter. How would I interpret the information provided to me in that section?

2. Dec 20, 2012

Staff: Mentor

There is a wide spread of hFE for this device. Furthermore, hFE also varies with collector current (there's a graph showing this). This tells you that whatever circuit you use, that circuit should be designed to be tolerant of a wide variation of hFE. Either that or you must individually test a handful of devices and pick the one with the highest gain. (Not advisable, as repair and replacement may well see the circuit not function.)

I think you'll find that the variation of hFE with VCE is of the same order, or overshadowed by, the variation of hFE with IC. You can judge for yourself if you unearth a plot of IC versus VCE on another manufacturer's datasheet: the more horizontal the lines, the less the variation.