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

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

3. Topic:
Diode & its
Approximations

4. 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.

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

6. 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

7. Bulk resistance:
 The sum of ohmic resistances is called Bulk
resistance
RB=RP+RN
 It depends on the size of the p and n regions
 The bulk resistance is less than 1(ohm)

8. Approximations

9. 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(2nd
approximation).Or may be 21 year and 9
months(3rd approximation).Or if you want
to be more accurate,21 year 9 months 3 days
30 minutes and 40 sec(exacts)

10. Ideal diode(1st
approximation)
Second Approximation
Third Approximation

11. Ideal DIODE(1st
approximation)

12. 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,
the model is an open switch

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

15. Second
Approximation

16. 2nd 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

18. third
approximation

19. 3rd 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)

20. the end