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In BJT for working in active region for a common emitter configuration emitter and base should be in forward bias and base and collector should be in reverse bias. But in case of voltage we say that base-collector voltage should be less than 0.4V.enter image description here

But if V(base)-V(collector)=0.1 (suppose) then base-collector junction will be in forward bias that means it will enter into saturation mode. But book says it will remain in active mode. How is it possible?

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  • \$\begingroup\$ For one, 0.1V isn't enough to bias any pn junction into conduction, unless you have some really weird semiconductor. \$\endgroup\$ – Hearth Apr 25 '17 at 12:51
  • \$\begingroup\$ that means i will not get any collector current? \$\endgroup\$ – Leolime Apr 25 '17 at 12:53
  • \$\begingroup\$ Carefully study the BJT in active mode again, The B-C PN junction will not be in forward mode to allow Ic to flow. So there will be a collector current despite the B-C junction being not forward biased. That is basically the whole point of a BJT in active mode. \$\endgroup\$ – Bimpelrekkie Apr 25 '17 at 12:55
  • \$\begingroup\$ No--it means your base-collector junction is not forward biased. \$\endgroup\$ – Hearth Apr 25 '17 at 12:55
  • \$\begingroup\$ then can i say that V(collector)-V(base)>-0.4V? \$\endgroup\$ – Leolime Apr 25 '17 at 13:00
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Here is a bipolar I_V plot; saturation is the far left region; notice all the lines merge in "saturation", not good for linear amplification but good for switches.

enter image description here

Here is the circuit used to produce that plot

schematic

simulate this circuit – Schematic created using CircuitLab

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