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In a voltage regulator circuit, a Zener diode with a breakdown voltage of 6 V is connected in parallel with a load resistor of 1.2 k . The diode and load are connected in series with a resistor of 200 to an unregulated DC voltage supply. If the current flowing through the Zener diode is measured to be 15 mA , the value of the unregulated input voltage is

Options

  1. A9 V
  2. B10 V
  3. C7 V
  4. D4 V

Correct answer

B. 10 V

Step-by-step solution

The load current I_L is given by I_L = V_Z R_L = 6 1200 A = 5 mA . By Kirchhoff's current law, the total current I_s through the series resistor is the sum of the Zener current and the load current: I_s = I_Z + I_L = 15 mA + 5 mA = 20 mA . The voltage drop across the series resistor is V_s = I_s R_s = 20 10⁻³ 200 = 4 V . Applying Kirchhoff's voltage law, the input voltage V_ in is: V_ in = V_Z + V_s = 6 + 4 = 10 V . Answer: 10 V

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