The Currents of BJT

1.     The collector current.

2.     The Emitter Current.

3.     The base Current.

Collector Current

                                It can be represented as   I_C=I_Se(V_BE/V_T)

                                                Is= saturation current or current scale factor.

The Base Current

                               It is presented through I_B=I_C/ β

        Where β is a constant for transistor and is called as common emitter current gain, as

                                                                                I_C/I_B=β

The Emitter Current

                        As the total current which enters a transistor must depart it, thus we may write

                                                                                I_E=I_B+I_C

                                                                                But IB=IC/ β

                                Hence,

                                                                                I_E=I_C+I_C/ β

                                Or

                                                                                I_E= I_C(β+1)/ β

                                Or

                                                                                I_E=  Is e(V_BE/V_T) (β+1)/ β

                                Otherwise, we may write

                                                                                I_C=αI_E                                    α= β/ (β+1)

                                Or                                           I_E=(I_s/α) e(V_BE / V_T)

                                We may also write

                                                                                β=α/(α-1)

                                                α is called as common base current gain.