Lecture# 05,06.pdf Basic electronics LEcture

Basic Electronics

1. Lecture # 05,06
•PN-Junction construction.
•Formation of Negative & Positive Ions.
•Pn-Junction diode.
•Depletion region.
•Potential barrier.
•Types of biasing.
1.Zero bias.
2. Forward bias.
3. Reverse bias.
•Applications of diode.

2. •A diode is formed by joining two materials P-
Type and N-Type semiconductor.
•The P-Type semiconductor has excess holes
and is of positive charge.
•The N-Type semiconductor has excess
electrons and is of negative charge. .
PN-Junction construction:

4. •A P-type material hasholesas themajority
carriersand an N-type material haselectronsin
majority carriers.
•When supply voltage, few holes from P-type go
to n-side, whereas few electrons from N-type go
to P-side.
•When both free electrons and holes travels
towards the junction that way positive and
negative ions form.
Formation of Negative & Positive Ions:

5. •When positive and negative ions are formed, that
is called PN junction or junction barrier.
Holes
Electrons
Dc supply

6. Pn-Junction diode:
•The diode was been invented in the year 1950.
•The diode is a device which current flows only one
direction.
•The diode has two terminals and two layers.
•The anode has positive side and cathode negative side.
•The diode has one Pn-junction.
•The diode decides whether condition is forward bias or
reverse bias.
•The potential barrier of silicon is 0.7v and germanium
0.3v.
•The diode is used for rectification.

7. P
N
A K

8. AC input
Pulsating dc output
Half wave Rectification:

9. Full wave Rectification:

10. • Depletion layer acts like a barrier that opposes the
flow of electrons from n-side and holes from p -
side.
Depletion region:

11. Negative charge on N-side then free
electrons to cross from N-side to P-side.
Positive charge on P-side then holes to
cross from P-side to N-side.
Potential barrier:

12. Potential barrier
Si= 0.7 & Ge.=0.3

13. Biasing:
•Biasing means applying the DC voltage on
device.
•In reverse, when voltage is applied ondiode then
no current flows becausediodedoes not work in
reverse bias. It is called reverse-biased.
•In forward bias, when voltage is applied on diode
then diode then diode conducts the current
because the diode work in forward-biased diode.
Itis called the forward bias.

14. Types of biasing:
1. zero bias.
2. Forward bias.
3. Reverse bias

15. 1. Zero bias:
When a diode is connected in aZero
Biascondition, no external potential energy is
applied to the PN junction. However, if the diodes
terminals are shorted together.
Initially when the forward bias voltage is zero, the
current through the diode is also zero. The current
through the diode is zero because there is no
voltage applied across its terminals which could
establish current.

16. Circuit diagram of zero bias

17. 2. Reverse bias:
• When a Reverse biascondition, a positive
terminal of battery or source is connected with
cathode and a negative terminal of battery or
source is connected with anode.
• In reverse bias the potential barrier is increased
and does not current flow in circuit.

18. Circuit diagram of reverse bias

19. 3. Forward bias:
•When a Forward Biascondition, a positive
terminal of battery or source is connected with
anode negative terminal of battery or source is
connected with cathode.
• If this external voltage becomes greater than the
value of the potential barrier, approx. 0.7 volts for
silicon and 0.3 volts for germanium then current
will start to flow.

20. Circuit diagram of forward bias

21. V-I characteristic of diode in forward bias:
•When positive terminal of supply is connected
with positive terminal of diode.
•When negative terminal of supply is connected
with negative terminal of diode.
• Now increase voltage from 0 or 0.2 or 0.4, no
current increase.
•The current start to increase in diode when voltage
reached on 0.5 then current increase slowly.
•When voltage reached on 0.7 then current increase
vary sharply.

22. P N
Circuit diagram of Forward bias:

23. V-I characteristic of diode in forward bias:

24. V-I characteristic of diode in reverse bias:
•When positive terminal of supply is connected
with negative terminal of diode.
•When negative terminal of supply is connected
with positive terminal of diode.
•Now increase voltage from 0 or 4 or 20, no
current increase b/c diode does not work in
revers bias.

25. P
N
Circuit diagram of Reveres bias:

26. 0.01μA
Leakage current

27. Applications of diode:
• Switching purpose.
•TV
•Monitor
•Diode use in all electronic & electrical
components

28. Close switch:
Switch

29. Open switch:
Switch