(i) Draw the V-I characteristics of a p-n junction diode. (ii) Differentiate between the threshold voltage and the breakdown voltage for a diode. (iii) Write the property of a junction diode which makes it suitable for rectification of ac voltages.
Solution
(i) The characteristic has a forward branch (negligible current until the knee, then a steep rise) and a reverse branch (a tiny saturation current until breakdown). (ii) The threshold (cut-in or knee) voltage is the forward voltage beyond which the forward current increases rapidly (~0.7 V for Si). The breakdown voltage is the reverse voltage at which the reverse current suddenly increases. (iii) A junction diode conducts appreciably only when forward biased, i.e. it allows current in one direction only; this unidirectional conduction is what makes it suitable for rectifying ac. Unidirectional conduction⇒rectification.
