The document covers the formation and characteristics of p-n junctions and diodes, detailing concepts such as barrier potential, forward and reverse bias conditions, and the diode equation. It explains the usage of diodes in various electronic applications, particularly in rectifying AC to DC. Key characteristics, including voltage drops for silicon and germanium, and different rectifier configurations, are also presented.

1. Basic Electronics
Lecture#6
PN Junction, Diode/
Diode Application.
By: sarmad baloch
Class of BS.IT, ISP

3. P-N Junction

4. Contents
1. PN Junction Formation
2. Space Charge Distribution
3. Barrier Potential
4. Forward Biased and Reverse Biased
Diode
5. Diode Equation
6. Diode Models
7. Schottky Diode

5. PN Junction Formation

6. PN Junction Formation

7. PN Junction Formation

8. PN Junction Formation
P-Type semiconductor
having excessive holes
N-Type semiconductor
having excessive free
electrons
Junction
Acceptor
atoms
Donor
atoms

9. Charge Distribution
P N
+
+
+
-
-
-
Positive and negative ions are
created when holes and free
electrons cross the junction and
move to the other side this charge is
called “space charge”
Diffusion
current flows
whenever P and
N materials are
joined together

10. The P-N Junction
•When initially joined
electrons from the
n-type migrate into the p-
type – less electron density
there
•When an electron fills a
hole – both the electron
and hole disappear as the
gap in the bond is filled
•This leaves a region with no free charge carriers – the depletion layer – this layer
acts as an insulator
Slide 10

11. Barrier Potential
P N
+
+
+
-
-
-
Charges of opposite polarities establish “Electric
Field” also known as “Barrier Potential”. This
field prevents any further diffusion current
E
Depletion Region
Barrier potential is also
known as “Junction
Potential” or “Diffusion
Potential”. It is denoted by Vo
.

12. Barrier Potential
• Silicon has potential barrier drop of
0.7V.
• Germanium has potential barrier
voltage drop of 0.3V.

13. DIODE
(Formed Using P-N Junction)

14. DIODE
• A PN Junction is also called DIODE.
• Term diode from the Greek roots di , meaning 'two',
and ode, meaning 'path'.
• It is used in various electronics application.
• We will use this diode to form transistor and FET.
• Same diode are also used to form logic circuit

15. DIODE SYMBOL, SIGN

16. Forward Biased Junction
+
+
+
-
-
-
E
NP
+ -
Opposing field due to battery
Depletion region
shrinks and drift
current begins to flow

17. Forward Biased Junction

18. Reverse Biased Junction
+
+
+
-
-
-
E
NP
+-
Supporting field due to battery
Depletion region
expands and opposes
flow of current

19. Reverse Biased Junction

20. DIODE Characteristics

21. To Remember!
•Diode cannot conduct in reverse bias condition.
•Diode can conduct in forward bias condition.
•Silicon diode has voltage drop of 0.7V
•Germanium has voltage drop of 0.3V

22. DIODE APPLICATION
RECTIFIER OR AC TO DC
CONVERSION

23. AC Voltage and Current:

24. AC Voltage and Current:

25. DC Voltage and Current:

26. AC And DC Voltage and Current:
 A.C: Change over time.  D.C: Doesn't change over
time.

27. Half Wave Rectifier
+
- Re
0
T/2 T 3T/2 2T 5T/2
DC Value ?

28. Full Wave Rectifier
+
-
0 T 2T 3T 4T 5T
DC Value ?

29. Using Capacitor
+
- Re C
0
T/2 T 3T/2 2T 5T/2
Positive cycle charges the capacitor and
negative cycle discharges it
Ripple Voltage

30. DC Output With Capacitor
0 T 2T 3T 4T 5T
+
-
R
C

31. Vac
Load
Full-wave rectifier circuit
• Bridge circuit
• Load
– Circuit requiring DC

32. Ripple Voltage
0 T/2 T 3T/2 2T 5T/2
Ripple Voltage
0 T/2 T 3T/2 2T 5T/2
Ripple Voltage
VDC VPP
VPR