A power diode is a two terminal p-n junction device and a p-n junction normally formed by allowing diffusion and epitaxial growth structure of a power diode and symbol are shown in figure below.
High power diodes are silicon-rectifiers that can operate at high junction temperatures.Power diodes have larger Power,Voltage and Current handling capabilities than ordinary signal diodes.In addition,the switching frequencies of power diodes are low as compared to signal diodes.
When the anode potential is positive with respect to cathode,the diode is said to be forward biased,the diode conducts and behaves essentially as a closed switch.A conducting diode has a relatively small forward voltage drop across it and the magnitude of the drop would depend on the manufacturing process and temperature.When cathode potential is positive with respect to anode,the diode is said to be reversed.It behaves essentially as an open circuit.Under reverse biased condition,a small reverse current is known as leakage current in the range of μA or mA flows and leakage current increases slowly in magnitude with the reverse voltage until the avalanche voltage is reached .The forward voltage drop when it conducts current ,is in the range of 0.8 to 1V.Diodes with ratings as high as 4000V and 2000A are available.
Following the end of forward conduction in diode,a reverse current flows for a short time.The device doesn’t attains its full blocking capability until the reverse current ceases.The reverse current flows in the interval called rectifier recovery time.During this time,charge carriers stored in the diode at the end of forward conduction are removed.The recovery time is in range of a few μs(1-5)μs in a conventional diode to several hundred nanoseconds in fast recovery diodes.This recovery time is of great significance in high frequency operation.The recovery characteristics of conventional and fast recovery diodes are shown in figure below.
The application of these devices includes electric traction,battery charging,electro plating,electro metal processing,power supplies,welding ups etc