MODEL OF DIODE WHEN THE DIODE IS FORWARD BIAS:

MODEL OF DIODE WHEN THE DIODE IS FORWARD BIAS:

  When the diode is forward bias there are three type of model can be studied.
          1.      Ideal model
          2.      Practical model
          3.      Complete model

IDEAL MODEL:

  In ideal model we assume the Vf means the drop voltage through the depletion considered as zero. So

            Vf = 0

By applying K.V.L rule we got                   

Model Diode

                                    

 Vbias – Vrlimit – Vf= 0

 Vrlimit = Vbias -     Vf                                                                              

Here 

        Vrlimit = Ir * Rlimit                                                                     

So

      Ir * Rlimit = Vbias – Vf                                                                   

And also note that Vf = 0

    Hence

      Ir=Vbias / Rlimit

PRACTICAL MODEL:

  In practical mode we considered the drop voltage through deletion region so we have Vf Is 0.7V thus the equation will be,

  Vf = 0.7V

By applying K.V.L rule we got    

Diode model

  Vbias – Vrlimit – Vf = 0

  Vrlimit = Vbias - Vf

Here 

  Vrlimit = Ir * Rlimit

Hence 

  Ir * Rlimit = Vbias – Vf

  Ir = Vbias – Vf/Rlimit

COMPLETE MODEL:

 In complete model we considered the total resistance in diode so we have Vf and r’d which is the resistance of depletion region.

So 

Diode model

    Vf= 0.7 + r’d

By K.V.L rule we got

    Vbias – Vrlimit – Vf = 0    

    Vrlimit = Vbias – Vf

Here

    Vrlimit = Ir (Rlimit + r’d)

    Ir (Rlimit + r’d) = Vbias – Vf

    Ir = Vbias – Vf/ (Rlimit + r’d)