In a given circuit diagram, a 5   V zener diode along with a series resistance is connected across a 50   V power supply. The minimum value of the resistance required, if the maximum zener current is 90   mA will be                 Ω.

Step-by-step solution

Voltage across, R L = 5   V ⇒ i 2 = 5 R L Also, voltage across R = 50 - 5 = 45 volt v = i R ⇒ R = v i = 45 i i + i 2 R = 45 90 m A + 5 R L Current in zener diode is maximum when R L → ∞ i 2 → 0 and i i = i So R = 45 90   mA = 500   Ω