A supply varies from 12 V to 18 V. A 6 V Zener regulator supplies load current from 0 to 20 mA. Zener current must remain between 5 mA and 50 mA. What single series resistance satisfies both extremes?
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Question

A supply varies from 12 V to 18 V. A 6 V Zener regulator supplies load current from 0 to 20 mA. Zener current must remain between 5 mA and 50 mA. What single series resistance satisfies both extremes?

G1 Physics · Accepted Answer

At 12 V and 20 mA load: R_s≤6/25 mA=240 Ω. At 18 V and zero load: R_s≥12/50 mA=240 Ω. Therefore R_s=240 Ω.