# Large signal current gain vs small signal current gain

large signal current gain hFE = (IC - ICBO)/(IB + ICBO)

and small signal current gain hfe = IC/IB

1. what is the difference between these two.
2. why cant we use large signal current gain in small signal currents??
3. i have these notes
on page 57 (page 1 on pdf) paragraph 2 of these (please go through the link)

Notes

A comparison of the simple model
with the iv characteristics of the
BJT shows that our simple largesignal model is very crude and is
not accurate for AC analysis.
The simple model cannot be used to calculate these changes
(It assume vBE is constant!).

how come we have VBE constant in large signal models??

Last edited:

NascentOxygen
Staff Emeritus