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hfe of NPN BJT at lower Vce values

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Hi,

hFE will be reduced. But not that much.
See Page 5, top left chart.
Follow the hFE curve for Ic/Ib = 50 to the Ic= 15mA point. VCE is about 0.075V.

--> You see even at Vce below 0.1V hFE is higher than 50

(choosing the other curve you see that at V_CE of about 0.025V hFE is further reduced to 10)

Klaus
 

Early voltage (VA) tells you the relation of beta to Vce
(until you approach saturation, then it all gets loose).
 

VA is the intercept point (negative) of any collector
I-V load line (they converge at a point, to the left of
Y axis).

At fixed Ib (as a curve tracer doing Ic-Vce sweeps
would impose on an individual sweep) the variation
of Ic means beta is varying. You could use the same
d__/dVce on beta, as extracted from the Ic load line.

The mechanism is base width reduction due to C-B
depletion region widening (eats a lot of collector side
and a bit of base side extent).
 
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Dick_freebird, thank you for the explanation.
I am aware of the mechanism of base width reduction and the influence on the Early voltage.
However, from your previous answer I have deduced that there could be a formula which clearly shows how VA influences the "relation of beta to Vce" (your words).
Of course, VA is a measure for the slope of the Ic=f(Vce) curve and, hence, has "something to do" with Ic variations (for Ib=const) and, hence, with variations of the current gain.
But is there a relation that can be given as a formula ? That was the background of my question.
 

The curves on a datasheet are for a "typical" device. If you design for a typical device then all the circuits you make using devices with spec's less than typical will not work. If you design using minimum spec's then all circuits you make will work well.
When you buy parts you get ones with maximum spec's and some with minimum spec's. You get whatever they have. If they all have passing but minimum spec's and your design used typical spec's then all of the circuits you make will not work.
 

The original question refers to "Vce much less than 10V", so it seems not to address Early effect but the current gain drop near to saturation.
 

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