Question 3-18B2

To determine the current-limiting resistor for a Zener diode voltage regulator, we first need to find the target current. The goal is to set the Zener bias to the midpoint of its operating range. 1. **Calculate the midpoint current (I_mid):** I_mid = (I_min + I_max) / 2 = (5 mA + 95 mA) / 2 = 100 mA / 2 = 50 mA. 2. **Calculate the voltage drop across the resistor (V_R):** The resistor drops the difference between the supply voltage and the Zener voltage. V_R = V_supply - V_Zener = 20 V - 10 V = 10 V. 3. **Apply Ohm's Law to find the resistor value (R):** R = V_R / I_mid = 10 V / 50 mA = 10 V / 0.050 A = 200 ohms. A 200-ohm current-limiting resistor will set the Zener diode's bias to the midpoint of its specified operating range, ensuring stable regulation under varying load conditions within its design limits. The Zener impedance and power rating are important characteristics for a complete regulator design but are not needed for this specific bias calculation.