The Forward Bias Region

• The forward bias or only forward region is entered while the terminal voltage v is +ve . In the forward region the i-v relationship is nearly approximated like

i = I_s(e^v/n V_T - 1)

• In this particular equation I_s is a constant for a mention diode at a mention temperature and this is directly proportional to the area of the diode.
• The Voltage V_T is a constant and indicated as

                                                             V_T = kT/q            

Here

                        k = Boltzmann,s constant = 1.38 x10^-23 jouls/kelvin

                        q =magnitude of the electronic ,charge =1.60 x10¹⁹coulombs

                          T= absolute temperature in kelvin

•   On room temperature (20 ^oC) the value of V_T will be 25.2mV.
•   In the diode equation the constant n contain a value between I & 2 based on the material & physical structure of the diode.
•   For considerable current I in the forward direction, i>> I_s. The diode equation may be altered like

                                                            i = I_s e^v/nVT   

 This expression may be alternatively given in algorithmic form

                                                v = nV_Tln(i/I_s)

•   Let us assume the forward i-v relationship & evaluate the current I₁ equivalent to the diode voltage V₁:

                                                 I₁ = I_se^V1/nVT

                                    Likewise, if the voltage V₂ the diode current I₂ is

                                                I₂ = I_s e^V2/nVT

                                    These two equations may be combined to generate

                                                     I₂/I₁ = e^{(V2 - V1)/nVT}

                                    That may be rewritten like

                                                                   V₂ - V₁ = nV_Tln(I₂/I₁)