This slide is designed as a teaching aid for students pursuing Module 4 in EASA B1 examination. There are a few topics not covered in this slide

1. MODULE 4.1
Semiconductors - Diode

2. Syllabus for Diode
 Diode symbols
 Diode characteristics and properties
 Diodes in series and parallel
 Main characteristics and use of silicon
controlled rectifiers (thyristors), light
emitting diode, photo conductive
diode, varistor, rectifier diodes;
 Functional testing of diodes

3. Diode and One Way Valve
 Diodes are similar to check valves.
 They allow fluid to flow in one direction
but not the reversed.


4. How Diode Works
 The PN junction consists of P and N
material joint together.
 The area where P material meets the N
material is called the junction.

5. Current in N-Type Material
 The flow is made up of
electron, similar to the
current in copper.
 The electrons leave the
crystal and flow towards
the positive terminals of
the battery.

6. Current Flow in P-Type
Material
 Holes flow within the
semiconductor from
+ve terminal to -ve.
 The flow external to
the semiconductor
is always electron.

7. Junction Barrier
 Both N and P types
of semiconductors
are electrically
neutral.
 The number of
electrons and
What happen, the electrons from N
material move to P material, thus creating
protons is balanced.
++ ions on N material.  We expected the
The hole transferred to N material.
This create a field barriers, ++ at N electrons will
material and -- at P material.
neutralize and
balance the
holes, but that do not

8. Barrier Junction
 Video

9. Forward Biased PN Junction

10. Reverse Biased PN junction
 Reverse biased
◦ No current due to
majority carrier.
◦ small current due to
minority carrier.
 Resistance
characteristic.
◦ Small resistance in
forward bias
◦ High resistance in in
reversed bias.
Refer to the
graph.

11. PN Junction Characteristic
 The resistance is
given by ohm’s
law.
 Example, forward
bias, at 1 v point,
R=250 ohms.
In reverse bias –
R= 800k.

12. Diode Identification…
 As there are many types of diode, a system is
required to identify it.
 The semi conductor identification is used to
distinguish one from the other.

13. …Diode Identification
 As there are many types of
diode, a system is required to
identify it.
 The semi conductor
identification is used to
distinguish one from the other.
• The first digit XN – X =is the number of junction. N =
a semiconductor.
• YYY – Identification Number.

14. Diode Markings
 There is the needs
to identify
anode/cathode
 The cathode is
marked as “k”, “+”
or color code or
band.


15. Diodes Color Code
 Example
◦ Brown, orange and
white bands
 Brown = 1
 Orange = 3
 White 9
◦ So the diode is
1N139

16. Diode Maintenance

17. Diode Maintenance…
 Diodes are rugged and design to last
a long time.
 Damages can be due to:
◦ Current overloads can damage the
junction
◦ Excess voltage
◦ High temperature. Heat increases the
current flow which in turn produce more
heat which will cause higher current.

18. … diode maintenance
 The followings are the precautions
when working with diodes:
◦ Power off when installing and removing diodes
◦ Do not use force to pull the diode from the PCB.
◦ Soldering diode need care to avoid excessive
heat.
◦ Replace of diode – must be direct replacement,
right direction.
◦ Avoid touching the exposed wires to avoid static
electricity.

19. Checking Diodes - analogue
 Checking Diode –
Positive lead is black
+ –  Why?
+ –

20. Checking Diodes digital
 Fwd bias – about 1  Reverse bias – open
K circuit.

21. Different Types of Diodes

22. … Different Types of Diodes
◦ Point Contact Diode
◦ PN Junction
◦ Schottky diodes
◦ Schottky Barrier Diode
◦ Varicap or varactor diode
◦ Zener diode

23. Different Types of Diodes …
 Different types of
diodes are
manufactured for
different purposes:
◦ Laser diode – the diode
produces laser light. The
laser generation function
is cheaper than the
alternative, however the
diode is more expensive
than other types of
diodes.

24. LED – Light Emitting Diode

25. Photodiode
 When light strikes, it produces
electrons or holes causing current
flow.
 Used to detect light.
 Typically photo-diodes are operated
under reverse bias conditions where
even small amounts of current flow
resulting from the light can be easily
detected.

26. Diode – PIN
Diode
 The pin diode acts as an ordinary diode at
frequencies up to about 100 megahertz,
but above this frequency the operational
characteristics change.
 The large intrinsic region increases the
transit time of electrons crossing the
region. Above 100 megahertz, electrons
begin to accumulate in the intrinsic region.
The carrier storage in the intrinsic region
causes the diode to stop acting as a
rectifier and begin acting as a variable
resistance.

27. Point Contact Diode
 A point-contact diode works the same as
the junction diodes, but their construction is
simpler.
 A block of n-type semiconductor is built, and
a conducting sharp-point contact made with
some group-3 metal is placed in contact with
the semiconductor.
 Some metal migrates into the semiconductor
to make a small region of p-type
semiconductor near the contact.
 The long-popular 1N34 germanium version is
still used in radio receivers as a detector and
occasionally in specialized analog
electronics.

28. Schottky Diodes
 Lower forward voltage drop about 0.15
– 0.4 v
 Different Construction – metal to
semiconductor contact
 Mainly used for clamping circuit

29. Schottky Barrier
Diodes
Use for rectification
 Shorter reverse time thus suited for
high frequency switching.

30. Diode Switching
Characteristics
 When diode is switched from forward biased
to reverse biased state or vice versa, it takes
finite time to attain a steady state.
 This time consists of a transient and an inter
val of time before the diode attain the steady
state is attained.

The behavior of the diode during this time is
called switching characteristics of the diode.
 In the forward-bias state, there are a large
number of electrons from the n side diffusing to
the p side.
 This diffusion process establishes a large nu
mber of minority carriers in each material

31. Zener Diode

32. RESOURCES
CAA UK Recommended Books
My Blog
Title Author ISBN
Aircraft Electricity and Eisman 0-02-801859-1
Electronics
Art of Electronics Horowitz 0-521-37095-7
Horowitz /Hill /Hill
Elements of Hickey/ 0070286957
Electronics Villines
Modern Aviation Helfrich 0-13-118803-8
Electronics
Micro Electronics in E Pallet 0-273-08612-X
Aircraft systems