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Deriving BJT Operating points in Active Region –An Example (2)

By Applying KVL to the collector emitter circuit

iC

10 mA

100 μA

80 μA

60 μA 40 μA 20 μA

VCC VCE IC = R CC

By using this equation along with the iC / vCE characteristics of the base collector junction, iC = 4 mA, VCE = 6V

0

20V vCE

β=

IC IB

=

4mA 40μA

= 100

Transistor power dissipation = VCEIC = 24 mW

We can also solve the problem without using the characteristics if β and VBE values are known 11

BJT in Cutoff Region

  • Under this condition iB= 0

  • As a result iC becomes negligibly small

  • Both base-emitter as well base-collector junctions may be reverse

biased

  • Under this condition the BJT can be treated as an off switch

12

6

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