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A Zener diode is used in a voltage regulator circuit to supply a constant voltage of 12 V to a load of 1.2 k . The unregulated input voltage fluctuates between 22 V and 36 V . If the maximum safe power dissipation of the Zener diode is 240 mW , the minimum value of the series resistance R_s required to protect the diode from damage is ________ .

Correct answer

800

Step-by-step solution

The maximum safe current that can flow through the Zener diode is determined by its power rating: I_ z, max = P_ max V_z = 240 mW 12 V = 20 mA The current flowing through the load resistor is constant and is given by: I_L = V_z R_L = 12 V 1.2 k = 10 mA The total current from the source must not exceed the sum of the load current and the maximum Zener current: I_ s, max = I_L + I_ z, max = 10 mA + 20 mA = 30 mA The most critical condition for the Zener diode occurs when the input voltage is at its maximum value ( 36

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