IGNOU PHE 10 2018 - Design a zener regulated power supply to give 9.1V DC output with maxi

Question

Design a zener regulated power supply to give 9.1V DC output with maximum load current of 50 mA. Assume that the minimum I_Z required for proper functioning of zener diode is 5 mA, and the unregulated DC input is 12V. Indicate the value of RS

and power ratings of zener diode and RS.

27 Jan 2018

Answer :

Word Count : 420

The zener diode is sensitive to temperature. Excessive temperature will destroy a zener diode, and because it both drops voltage and conducts current, it produces its own heat in accordance with Joule’s Law (P=IE). Therefore, one must be careful to design the regulator circuit in such a way that the diode’s power dissipation rating is not exceeded. Interestingly enough, when zener diodes fail due to excessive power dissipation, they usually fail shorted rather than open. A diode failed in this manner is readily detected: it drops almost zero voltage when biased either way, like a piece of wire.

Let’s examine a zener diode regulating circuit mathematically, determining all voltages, currents, and power dissipations. Taking the same form of circuit shown earlier, we’ll perform calculations assuming a zener voltage of 12.6 volts, a power supply voltage of 45 volts, and a series resistor value of 1000 Ω (we’ll regard the zener voltage

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