The junction diode in the following circuit requires a minimum current of 1 mA to be above the knee point (0.7 V) of its I-V characteristic curve. The voltage across the diode is independent of current above the knee point. If = 5 V, then the maximum value of R so that the voltage is above the knee point, will be
(a) 4.3 k (b) 860 k
(c) 4.3 (d) 860
(a) At knee point voltage across the diode is 0.7V.
Hence voltage across resistance R is 5 – 0.7 = 4.3 V.
using V = iR 4.3 = 1 R R = 4.3 k.