Zener Diode and Voltage Regulation - UNSOLVED PRACTICE SET
Chapter: Semiconductor Electronics | Topic: Zener Diode and Voltage Regulation
ZENER DIODE AND VOLTAGE REGULATION - UNSOLVED PRACTICE SET
Topic: Zener Diode and Voltage Regulation
Multiple Choice Questions
Q1. A Zener diode is specially designed to operate in:
- Forward bias only
- Reverse bias near breakdown region
- Unbiased condition
- Both forward and reverse bias equally
Q2. Zener breakdown occurs mainly due to:
- Collision of accelerated charge carriers with atoms
- Strong electric field causing direct rupture of covalent bonds
- Thermal ionization
- Photoelectric effect
Q3. Avalanche breakdown occurs mainly due to:
- Strong electric field alone
- Collision of accelerated charge carriers with atoms, causing ionization
- Thermal effects only
- Doping with trivalent impurities
Q4. Zener breakdown typically occurs in diodes with:
- Very low doping
- Moderate to high doping
- No doping
- Very wide depletion region
Q5. In a Zener voltage regulator circuit, the Zener diode is connected:
- In series with the load
- In parallel with the load
- In series with the input voltage
- Across the input only
Q6. The dynamic resistance of a Zener diode in the breakdown region is:
- Very high
- Very low
- Infinite
- Equal to the load resistance
Short Answer Questions
Q7. What is a Zener diode? How does it differ from an ordinary p-n junction diode?
Q8. Distinguish between Zener breakdown and avalanche breakdown in terms of mechanism and doping concentration.
Q9. Draw the V-I characteristic of a Zener diode and label the Zener breakdown region.
Q10. Why is a Zener diode used as a voltage regulator? Draw a simple Zener regulator circuit.
Q11. What is the significance of the dynamic resistance of a Zener diode in the breakdown region?
Q12. Why does the temperature coefficient of a Zener diode change from negative to positive as the Zener voltage increases?
Long Answer Questions
Q13. Explain the working of a Zener diode as a voltage regulator. Draw the circuit diagram and explain how it maintains constant output voltage despite variations in input voltage and load current.
Q14. Distinguish between Zener breakdown and avalanche breakdown. Explain the physical mechanisms involved in each and discuss how the breakdown voltage depends on doping concentration.
Q15. Discuss the factors that affect the performance of a Zener voltage regulator. How do you select the appropriate series resistor and Zener diode for a given application?
Numerical & Application-based Problems
Q16. A Zener diode has a breakdown voltage V_Z = 6 V and a maximum power dissipation of 500 mW.
(a) Calculate the maximum current that can flow through the Zener diode.
(b) The Zener diode is used in a regulator circuit with input voltage V_in = 12 V and load resistance R_L = 200 ฮฉ. Calculate the value of the series resistor R_s required.
(c) Calculate the minimum value of R_s if the load is disconnected.
Q17. A Zener regulator circuit has V_in = 15 V, V_Z = 9 V, R_s = 100 ฮฉ, and R_L = 300 ฮฉ.
(a) Calculate the current through the series resistor.
(b) Calculate the current through the load.
(c) Calculate the current through the Zener diode.
(d) If the input voltage increases to 18 V, calculate the new Zener current (assume V_Z remains constant).
Q18. In your school electronics lab, a student is building a regulated power supply.
(a) She uses a 9 V Zener diode to regulate a 12 V unregulated supply. The load requires 50 mA at 9 V. Calculate the value of the series resistor and the power rating required for it.
(b) The student then tests the circuit with the load disconnected. Calculate the current through the Zener diode and check whether it exceeds the maximum Zener current of 100 mA.
(c) She replaces the Zener diode with a 5 V Zener and wants to power a USB device (5 V, 500 mA). Explain why a simple Zener regulator is not suitable for this application and what additional components would be needed.
(d) A classmate suggests using two Zener diodes in series to get a higher regulated voltage. Explain whether this would work and how to calculate the output voltage.
(e) In India, voltage fluctuations are common in rural areas. Explain how Zener regulators protect sensitive electronic devices like TVs and computers from damage due to overvoltage.