Current Electricity and Electrical InstrumentHard

Question

A zener diode, having breakdown voltage equal to 15 V, is used in a voltage regulator circuit shown in the figure. The current through the diode is
       

Options

A.5 mA
B.10 mA
C.15 mA
D.20 mA

Solution

          
The vltage drop across 1 k Ω = Vz = 15 mA
The current through 1 k Ω is
     = 15 × 10-3 A = 15 m A
The vltage drops across 250 Ω = 20 V - 15 V = 5 V
Current through 250 Ω is
     = 0.02A = 20 mA
The current through the zener diode is
Iz = I - I′ =(20 - 15) mA = 5 mA

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