Circuit Diagram, Operations, Calculation, Formula, Advantages, Disadvantages, Solved Example Problem
Subject and UNIT: Electron Devices and Circuits: Unit I: PN Junction Devices
• In half wave rectifier, rectifying element conducts only during positive half cycle of input a.c. supply. The negative half cycles of a.c. supply are eliminated from the output.
Important characteristics
Subject and UNIT: Electron Devices and Circuits: Unit I: PN Junction Devices
Key Point : A rectifier is a device which converts a.c. voltage to pulsating d.c. voltage, using one or more p-n junction diodes.
PN Junction Diode
Subject and UNIT: Electron Devices and Circuits: Unit I: PN Junction Devices
• We have seen that a diode has a very important property that it permits only unidirectional conduction. It conducts very well in forward direction when forward biased and conducts very poorly in reverse direction when reverse biased.
PN Junction Diode
Subject and UNIT: Electron Devices and Circuits: Unit I: PN Junction Devices
• During forward biased condition, an another capacitance comes into existence called diffusion capacitance or storage capacitance, denoted as CD
PN Junction Diode
Subject and UNIT: Electron Devices and Circuits: Unit I: PN Junction Devices
• As seen earlier, when a diode is reverse biased, reverse current flows due to minority carriers. Majority charged particles i.e. electrons in n-region and holes in p-region move away from the junction. This increases the width of the depletion region.
Subject and UNIT: Electron Devices and Circuits: Unit I: PN Junction Devices
Let us study the derivation of the mathematical expression for the current through a diode, which gives its V-I characteristics.
Subject and UNIT: Electron Devices and Circuits: Unit I: PN Junction Devices
• The mathematical representation of V-I characteristics of diode is called V-I characteristic equation or diode current equation. It gives the mathematical relationship between applied voltage V and the diode current I.
Effect of Temperature, Advantages, Disadvantages, Applications
Subject and UNIT: Electron Devices and Circuits: Unit I: PN Junction Devices
The complete V-I characteristics of a diode is the combination of its forward as well as reverse characteristics. This is shown in the Fig. 1.8.1.
Subject and UNIT: Electron Devices and Circuits: Unit I: PN Junction Devices
• If an external d.c. voltage is connected in such a way that the p-region terminal of a p-n junction is connected to the negative of the battery and the n-region terminal of a p-n junction is connected to the positive terminal of the battery, the biasing condition is called reverse biasing of a p-n junction.
Subject and UNIT: Electron Devices and Circuits: Unit I: PN Junction Devices
Key Point : Forward biasing means connecting p-region to +ve and n-region to -ve of the battery.
Symbol, Biasing, Types
Subject and UNIT: Electron Devices and Circuits: Unit I: PN Junction Devices
• The p-n junction forms a popular semiconductor device called p-n junction diode. The p-n junction has two terminals called electrodes, one each from p-region and n-region. Due to the two electrodes it is called diode i.e. di + electrode.
Subject and UNIT: Electron Devices and Circuits: Unit I: PN Junction Devices
• In a given material if the doping is not uniform then at one place large number of charge carriers exist while at other place small number of charge carriers exist.