Diode & its Approximation

This presentation gives information about DIODE(a semiconductor device with two terminals, typically allowing the flow of current in one direction only). And also its Approximation

1. Group members: Kashaf Ejaz 15331553-092 Pakeeza Zainab 15331556-087

2. Topic: Diode & its Approximations

3. Introduction: Diode: A nonlinear device. The graph of current vs.voltage is not a straight line. The diode voltage must exceed the barrier voltage to conduct.

4. The diode symbol looks like an arrow that points from the p side to the n side .

5. Knee voltage: The voltage at which the current starts to increase rapidly is called the knee voltage of the diode The knee voltage is equal to the barrier potential Vk =0.7v( aproximately equal) For silicon diode barrier potential is 0.7v .And for germanium diode barrier potential is 0.3v

6. Bulk resistance: The sum of ohmic resistances is called Bulk resistance R B =R P +R N It depends on the size of the p and n regions The bulk resistance is less than 1(ohm)

7. Approximations

8. APPROXIMATION: We use approximations all the time in every day life.If someone ask you how old you are,you might answer 21 (ideal). Or you might say 21 going on 22 (2 nd approximation). Or may be 21 year and 9 months (3 rd approximation). Or if you want to be more accurate,21 year 9 months 3 days 30 minutes and 40 sec(exacts)

9. Ideal DIODE(1 st approximation)

10. First approximation: This represent the diode as being ideal . The first approximation ignores leakage current,barrier potential and bulk resistance When an ideal diode is forward biased,the model is a closed switch When an ideal diode is reverse biased, t he model is an open switch

11. Example: An ordinary switch has zero resistance when closed and infinite resistance when open.(Therefore an ideal diode acts like a switch)

12. Second Approximation

13. 2 nd approximation: This model assumes that no diode current flows until the forward bias across the diode reaches 0.7 volts This model ignores the exact shape of knee This model ignores the bulk resistance

14. third approximation

15. 3 rd approximation: This model assumes that no diode current flows until the forward bias across the diode reaches 0.7v This model ignores the exact shape of knee This model does account for the diode bulk resistance However,the bulk resistance that is less than 1(ohm) can be ignored)

16. the end