A Zener diode with a Zener voltage of 5 V and a maximum safe current rating of 40 mA is used in a voltage regulator circuit. It is connected to an unregulated DC supply of 15 V through a series resistor R_s . If the load resistor is disconnected (open circuit condition), what is the minimum value of the series resistance R_s (in ) required to protect the Zener diode from damage?

Step-by-step solution

When the load is disconnected, the entire current from the source passes through the Zener diode. This represents the worst-case scenario for the Zener current. For the Zener diode to operate safely, the current through it must not exceed its maximum rating, I_ z( ) = 40 mA = 0.04 A . The voltage drop across the series resistor R_s is given by the difference between the input voltage and the Zener voltage: V_s = V_i - V_z = 15 V - 5 V = 10 V Using Ohm's law, the minimum series resistance is: R_ s( ) = V_s I_ z( ) =