Common-Emitter Configuration

Common emitter configuration is represented below:
Circuit Relationships are given as follows

For base-emitter circuit,
iB =(VBB-VBE(on))/RB

For collector and emitter currents,
iC = beta*iB and iE = (beta + 1) iB

For collector-emitter circuit
VCC = i CRC + VCE

Common-Emitter Configuration(npn)
At base current = zero,
VBE = VBB

At emitter-base voltage = zero,
i BE =VBB /RB


Base-Emitter Load Line (npn)

Collector-Emitter Relationships

For circuit,
iC=VCC –VCE/RC

At collector current = zero,
VCE = VCC

At collector-emitter voltage = zero,
Ic=VCC /RC

As iB increases or decreases,Q point moves up or down load line.If iB increases too much,Q point is pushed into saturation region.If IC < (beta)*IB , Then Saturation occurs and VCE(sat) is typically 0.1 to 0.3 V

Applications of BJT

Generally for analog circuits,Want to operate in only the forward active region.Generally for digital circuits we want to operate the device between cut-off and saturation regions.