Vce < Vbe will cause a BJT to be in saturation mode. How is it possible that Vce < Vbe will forward bias both the PN junction in a NPN transistor?

 

If Vbe is about -0.7V and Vce is about -0.3V then the base-collector diode (NP) will be forward biased. The collector is more positive than the base.

 

Vce < Vbe will cause a BJT to be in saturation mode. How is it possible that Vce < Vbe will forward bias both the PN junction in a NPN transistor?

Vbe+Vcb=Vce, hence Vbc=Vbe-Vce

As an example, if Vce=0.2 V and Vbe=0.7V, then Vbc=0.5V which is forward biasing of the base-collector junction.

 

If Vbe is about -0.7V and Vce is about -0.3V then the base-collector diode (NP) will be forward biased. The collector is more positive than the base.

mik3,

Did you misread his post and think that he said PNP transistor?

 

mik3,

Did you misread his post and think that he said PNP transistor?

Yes!

 

When Vce < Vbe a chunk of the collector current flows back through the base, which is one of the reasons why a transistors gain is so low in the saturation region.

There is no universally agreed definition of saturation - Vce < Vbe is as good as any; another popular rule of thumb is Ic <= 10xIb.