8.5 Diode Transients

The pn junction is typically used as an electrical switch . A voltage or current pulseis applied to change the operating state between forward bias（‘on’ state）and reverse bias（‘off’ state）. Since a pn junction has capacitance associated with it，it would be expected that some time would be required to make the transition from off to on（turn-on time）and from on to off（turn-off time）. These transientsare discussed qualitatively.

Of primary interest in circuit applications is the speed of the pn junction diode in switching states. Usually the turn-off time is much larger than the turn-on time，and the total turn-off time is the sum of storage time tS and fall time t2.