i C =α F i E i C =i S [ exp ( V BE V T ) −1] β F = α F 1−α F i C =β F i B i B = i S β F [ exp ( V BE V T ) −1 ] α F = β F β F +1 i E =( β ¿¿ F+1 ) i B ¿ i E = i S α F [ exp ( V BE V T ) −1 ] i E =i B +i C exp ( V BE V T ) ≫ 1 ∴ exp ( V BE V T ) −1=¿ exp ( V BE V T ) General NPN BJT Mode Condition Behavior Cutoff V BE <0 V BC <0 i C =i E =i B =0 V BE <0.5 V V BC <0.4 V Active V BE >0 V BC <0 V BE =0.7 V CE >0.3 saturatio n V BE >0 V BC >0 V BE =0.7 V V CE sat =0.2 V i C i B =β Forced Common Emitter NPN BJT Mode Condition Behavior Cutoff V ¿ <V BE on V BE = V ¿ i B =0 i C =0 V CE = V CC Active V ¿ >V BE on V CE >V CE sat V BE = V BE on i B = V ¿ − V BE on R B i C =βi B V CE = V CC −i C R C Saturat ion V ¿ >V BE on V CE <V CE sat V CE = V CE sat ≅ 0.2 V i B = V ¿ − V BE on R B i C = V CC −V CE sat R C V BE = V BE on Mode EBJ CBJ Acting Cutoff Rev Bias Rev Bias Open sw. Active Fwd Bias Rev Bias Good amp. Saturat ion Fwd Bias Fwd Bias Closed sw. Rev. Active Rev Bias Fwd Bias Poor amp.