Transition capacitance , Diffusion capacitance in English

TRANSITION CAPACITANCE When diode is reverse biased reverse current flows through junction due to minority charge carriers. Majority charge carriers that is holes in P region and electrons in N region move away from the junction due to battery potential. Thus, width of Depletion layer increases with Reverse voltage. As charge particles move away from the junction, charge change with respect to applied voltage So the change in charge dQ with respect to change in charge dV is capacitive effect. Such capacitance is called as Transition capacitance, depletion layer capacitance or space charge capacitance. This capacitance is not constant but depends on magnitude of reverse bias voltage. Its equation is: CT=dQ/dV=εA/d ε is permittivity of semiconductor, A is area of cross section of junction and W is width of depletion layer. CT is inversely proportional to W. DIFFUSION CAPACITANCE The capacitance in forward bias condition of diode is called as diffusion capacitance and is denoted by CD. It is also called as storage capacitance. In forward bias, the width of depletion layer reduces and holes from p side diffuse to n side and electrons from n side diffuse to p side. As the applied voltage increases concentration of injected charge carriers increases This rate of change of injected charge with applied forward voltage is defined as capacitance known as diffusion capacitance. And depletion layer acts as dielectric of capacitor The equation of diffusion capacitance is CD=dQ/dV=τI/ηVT Where τ is mean life time of carrier, VT is voltage equivalent of temperature. Diffusion capacitance is proportional to forward current. CD is much greater than CT CD and CT both appear parallel to diode. -~-~~-~~~-~~-~- Please watch: "TRANSISTOR, Construction, Biasing in BJT in hindi" https://www.youtube.com/watch?v=lD-GchZJWf8 -~-~~-~~~-~~-~-