The most common application of diode is rectification.The rectifier diodes are used in power supplies to convert ac voltage into dc voltage.Some of the more common special purpose diodes are
- Zener diode
- Light emitting diode
- photo diode
- Varactor diode
- Tunnel diode
- opto coupler
Zener diode :
A zener diode is a special type of diode that is designed to operate in the reverse breakdown region.It is heavily doped PN junction diode.
The symbol and v-i characteristics of zener diode is shown in fig
An ordinary diode operated in this region will usually be destroyed due to excessive current.A zener diode heavily doped to reduce the breakdown voltage.This causes a very thin depletion layer.As a result,a zener diode has a sharp break down voltage (Vz).This is very clear from reverse characteristics.As the curve reveals,two things happen when Vz is reached.
(i)The diode current increases rapidly.
(ii)The reverse voltage Vz across the diode remains almost constant.
Light-Emitting diode :
LED is a specially made forward biased PN junction diode,which emits the light when current flows through it.
The color of light emits diode depending upon the type of material used as given in below.
(i) GaAs : Infrared radiation
(ii)Gap : Red or Green light
(iii)GaAsP : Red or Yellow light
LED is a solid state light source.LED have replaced incandescent lamp in many application because they have following advantages.
(i)low voltage
(ii)longer life (more than 20 years)
(iii)fast on-off switching.
A LED that emits one color when forward biased and another colour when reverse biased is called a multi-color LED.Multi-color LED's are typically red when forward biased in one direction and green when biased in the another.
No comments:
Post a Comment