PN Junction Diodes: Anna University Part B Important Questions and Answers

Electron Devices

Chapter 2: PN Junction Diodes

Important Part B Questions

 1. What is a p‒n junction?

2. Explain the basic structure of p‒n junction.

3. Explain the theory of p‒n junction.

4. Explain the formation of depletion region in an unbiased p‒n junction, with the help of neat sketch.

5. Briefly explain about depletion region and barrier voltage of a PN junction.

6. Draw and explain the energy band structure for open circuited p‒n junction.

7. Derive the expression for the built in potential barrier.

8. Consider a step graded germanium p‒n junction. It has N_D=10³ N_A and N_A corresponds to 1 atom per 10⁸ germanium atoms. Calculate the junction potential.

Assume n_i = 2.5×10³ cm³, atom density of Ge = 4.4 × 10²² atoms per cm³. [Ans. : 0.328 V]

9. Draw the symbol of p‒n junction diode. What are ohmic contacts ?

10. What is biasing of p‒n junction diode ?

11. Discuss the construction of p‒n junction diode.

12. With a neat diagram explain the working of a PN junction diode in forward bias condition.

13. Explain the static and dynamic resistances of the diodes.

14. Explain the V‒I characteristics of diode in forward biased mode.

15. With necessary diagram, describe the characteristics of a forward biased PN junction diode.

16. With a neat diagram explain the working of a PN junction diode in reverse bias condition.

17. Explain the V‒I charactersics of diode in reverse biased mode.

18. Explain briefly : i) Avalanche breakdown ii) Zener breakdown.

19. With necessary diagram, describe the characteristics of a reverse biased PN junction diode.

20. Draw and explain the V‒I characteristics of a PN junction diode.

21. Draw and compare V‒I characteristics of typical Ge and Si diodes.

22. Explain the current components in a p‒n junction diode.

23. Write the diode current equation of a p‒n junction and explain the V‒I characteristics from it.

24. The current of germanium diode is 100 μA at a voltage of ‒1 V, at room temperature. Determine the magnitude of the current for the voltages of ± 0.2 V at room temperature.

[Ans.: 291 mA, 99.95 μA ]

25. A silicon diode has a reverse saturation current of 60 nA. Calculate the voltage at which 1 % of the rated current will flow through the diode, at room temperature if diode is rated for 1 A. [Ans. : 0.6252 V]

26. Explain the theory of PN junction diode and derive its diode current equation.

27. Derive the p‒n diode current equation.

28. Derive the expression for the dynamic resistance of a diode.

29. For a silicon diode with reverse saturation current of 0.2 μA, calculate the dynamic forward and reverse resistance at a voltage of 0.72 V and ‒0.72 V respectively, applied across the diode, at room temperature of 27 °C.

[Ans. : 0.252 Ω, 2680.9 GΩ]

30. What is the effect of temperature on cut‒in voltage and reverse saturation current ?

31. Explain the effect of temperature on the diode characteristics.

32. A p‒n junction silicon diode has a reverse room saturation current of 50 nA at the temperature 27 °C. If the new reverse saturation current is observed to be 160 nA, calculate the new temperature. [Ans.: 44.19°C]

33. The reverse of saturation current silicon diode is found to be 50 nA at 27 °C. In a certain circuit the junction temperature is observed to rise up to 105 °C. Calculate the value of new reverse current. [Ans.: 9.79 μA]

34. A silicon diode operates at a forward voltage of 0.4 V. Calculate the factor by which the current will be multiplied when the temperature is increased from 25 °C to 150 °C. [Ans. : 476.29]

35. Explain the concept of transition capacitance of p‒n junction diode.

36. Derive the expression for the capacitance of p‒n junction diode.

37. Explain the concept of diffusion capacitance of a p‒n junction diode.

38. Derive the expression for the diffusion capacitance of p‒n junction diode.

39. Explain the switching characteristics of diode with the help of simple diode circuit.

40. Write short notes on diode switching characteristics.