08-16-2017, 10:20 PM
Biasing a diode means applying appropriate DC voltage to a diode. A forward biased diode conducts
easily whereas reverse biased diode practically conducts no current. It means that forward resistance of a
diode is quite small as compared with its reverse resistance.
Forward current is the current flowing through a forward biased diode. Every diode has a maximum
value of forward current, which it can safely carry. If this value is exceeded, the diode may be destroyed
due to excessive heat. Reverse current or leakage current is the current that flows through the reverse
biased diode. This current is due to the minority carriers. Under normal operating voltages the reverse
current is quite small. Its value is extremely small for silicon diodes but it is appreciable for germanium
diodes. Peak inverse voltage is the maximum reverse voltage that a diode can withstand without
destroying the junction. If the reverse voltage across a diode exceeds this value, the reverse current
increases sharply and breaks down the junction due to excess heat. Peak inverse voltage is important
when diode is used as a rectifier.
Zener diode is a heavily doped PN junction diode, meant to operate in reverse bias condition. The
breakdown or zener voltage depends upon the amount of doping. If the diode is heavily doped, depletion
layer will be thin and consequently the breakdown of the junction will occur at a lower reverse voltage.
On the other hand, a lightly doped diode has a higher breakdown voltage. When zener diode is forward
biased, its characteristics are just same as ordinary diode.