Question

Time taken for a diode to reach 90% of its final value when switched from steady state is______

(a) 2.3*time constant

(b) 2.2*time constant

(c) 1.5*time constant

(d) equals the time constant

This question was addressed to me in an interview.

This intriguing question originated from PN Diode Switching Times topic in division Semiconductor-Diode Characteristics of Electronic Devices & Circuits

Answer 1

The correct choice is (b) 2.2*time constant

Best explanation: Time constant = RC. To reach 90% of the final value, time taken is 2.2 of RC. Time constant is the time required to discharge the capacitor, through the resistor, by 36.8%.