Question.
What are the characteristic of a PN junction diode, point out
its specifications. Also point the significance of dynamic and static resistance.
Diode is a one way device, offering low resistance when
forward biased and behaving almost as an insulator when reverse biased
Characteristic can be categorised as
Forward and reverse characteristic.
Forward characteristic.
The diode starts to conduct only when its barrier voltage Vb is overcome, when forward biased.
For Si = 0.7V for Ge = 0.3v
As soon as Vb is overcome, current
increases rapidly.
Forward [DC] resistance – opposition offered by diode to
forward DC
Rf [Forward diode resistance] = OA /
AC forward resistance = opposition offered to charging
forward current
AC forward resistance = change in voltage / change in forward
current
Reverse characteristic.
When the diodes are reverse biased, only a small current flows
through the diode. As reverse voltage is increased, reverse current quickly
reaches its saturation value Io
Also known as leakage current.
As reverse voltage is increased beyond a certain value, i.e. breakdown
voltage / zener voltage, the leakage current suddenly
and sharply increases.
Static characteristic
The [V-I ] characteristic discussed
above is called Static characteristic because it describes the DC behaviour of
the diode.
Dynamic characteristic
This refers to action of diode under alternating current
