Derivation of npn BJT emitter,base and collector currents in forward active mode
Essentially BJT is just two neighboring pn junctions put back to back. BJT: a first pass (7.2) Fact In an IC npn transitor the emitter donor concentration \(N_{dE}\) is much greater than the base acceptor concentration \(N_{aB}\) which is much greater than the collector donor concentration \(N_{dC}\) \[ N_{dE}\gg N_{aB}\gg N_{dC} \] therefore the thermal equilibrium minority carrier concentrations in the emitter, base, and collector are \[ p_{nEo}=\frac{n^2_i}{N_{dE}}\ll n_{pBo}=\frac{n^2_i}{N_{aB}}\ll p_{nCo}=\frac{n_i^2}{N_{dC}} \] Forward-active regime: edge minority carrier concentration profile vs that of thermal equilibrium. Assume steady state short base diode conditions You should realize the heights of the thermal equilibrium minority carrier concentrations drawn in diagram above is a direct consequence of Fact 70 . This will again will be represented in the diagram Figure fluxpath where we account for flux paths of minority ca...