A zener diode having zener voltage 8 V and power dissipation rating of 0.5 W is connected across a potential divider arranged with maximum potential drop across zener diode is as shown in the diagram. The value of protective resistance Rp is ______ Ω.
Answer: 192
Solution
The potential divider is set for the maximum drop, so the whole supply of 20 V appears across Rp in series with the zener diode. The largest current the diode may carry follows from its power rating:
IZ=VZP=80.5=161A
The protective resistance carries this same current and takes up the remaining 20−8=12 V, so