# BJT's Saturation Region

Discussion in 'Homework Help' started by khiawyen, May 5, 2009.

1. ### khiawyen Thread Starter New Member

Nov 17, 2008
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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?

2. ### mik3 Senior Member

Feb 4, 2008
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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.

3. ### steveb Senior Member

Jul 3, 2008
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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.

4. ### steveb Senior Member

Jul 3, 2008
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mik3,

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

Feb 4, 2008
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Yes!

6. ### Darren Holdstock Active Member

Feb 10, 2009
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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.