A voltage regulator circuit is constructed using a Zener diode with a breakdown voltage of 8 V . The diode is connected in parallel with a load resistor of 400 . A series resistor of 200 connects this parallel combination to a DC power supply of unknown voltage V . If the current flowing through the Zener diode is 15 mA , what is the value of the supply voltage V ?

Step-by-step solution

The current through the load resistor is given by Ohm's law, as the voltage across it is clamped by the Zener diode: I_L = V_Z R_L = 8 400 A = 20 mA The total current I_S flowing through the series resistor is the sum of the Zener current and the load current: I_S = I_Z + I_L = 15 mA + 20 mA = 35 mA Applying Kirchhoff's voltage law, the supply voltage V is the sum of the voltage drop across the series resistor and the Zener voltage: V = I_S R_S + V_Z V = (35 10⁻³ 200) + 8 V = 7 + 8 = 15 V Answer: 15 V