Static V- I Characteristics

The  static V- I  characteristics of power diodes is shown  in figure 1.2  when the  anode is made  positive with  respect to cathode the power  diode  is said  to be forward  biased. In  this condition the power diode behaves as a closed switch. As the anode  voltage  is increased the current will initially be zero  until  the voltage  is less than its threshold  voltage  is the minimum  anode voltage  beyond which the diode current  increases rapidly and diode  starts conducting. A conducting diode has a relatively small  forward voltage drop across. It  the magnitude of the forward voltage  drop depends son the manufacturing  process and temperature.

                                                               Figure Static V- I Characteristics of power diode

When  cathode  of power  diode is made  positive  with respect to anode  the diode  is said  is to be reversed. It  reversed. It  behaves as an  open  circuit. Under reverse biased  condition a small reverse current  flows and this  reverse current  is known as leakage current leakage current increase slowly  in magnitude with the  reverse voltage until the avalanche voltage  is reached. The  avalanche breakdown is a process that occurs  in a diode when high voltage  causes free electrons to travel at high  speeds  colliding with other electrons and  knocking  them out of their  orbits. The  result is  a rapidly increasing amount  of  free electrons  and hence increased current. The  can be  limited by connecting a  resistance in  series  with the  power diode.