easa part 66 module 4 diode
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Syllabus for DiodeDiode symbols Diode characteristics and properties Diodes in series and parallelMain characteristics and use of
silicon controlled rectifiers (thyristors), light emitting diode, photo conductive diode, varistor, rectifier diodes;
Functional testing of diodes
Diode and One Way ValveDiodes are similar to check
valves.They allow fluid to flow in one
direction but not the reversed.
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.
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.
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.
Junction Barrier
Both N and P types of semiconductors are electrically neutral.
The number of electrons and protons is balanced.
We expected the electrons will neutralize and balance the holes, but that do not happen
What happen, the electrons from N material move to P material, thus creating ++ ions on N material.The hole transferred to N material.This create a field barriers, ++ at N material and -- at P material.
Forward Biased PN Junction
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.
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.
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.
…Diode IdentificationAs 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.
Diode MarkingsThere is the
needs to identify anode/cathode
The cathode is marked as “k”, “+” or color code or band.
Diodes Color CodeExample
◦ Brown, orange and white bands Brown = 1 Orange = 3 White 9
◦ So the diode is 1N139
Diode Maintenance
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.
… diode maintenanceThe 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.
Checking Diodes - analogue
Checking Diode – Positive lead is black
Why?+ –
+ –
Checking Diodes digital
Fwd bias – about 1 K
Reverse bias – open circuit.
Different Types of Diodes
… Different Types of Diodes
◦Point Contact Diode◦PN Junction◦Schottky diodes◦Schottky Barrier Diode ◦Varicap or varactor diode◦Zener diode
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.
LED – Light Emitting Diode
PhotodiodeWhen 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.
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.
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.
Schottky Diodes
Lower forward voltage drop about 0.15 – 0.4 v
Different Construction – metal to semiconductor contact
Mainly used for clamping circuit
Schottky Barrier Diodes
Use for rectification Shorter reverse time thus suited
for high frequency switching.
Diode Switching CharacteristicsWhen 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 interval 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 number of minority carriers in each material
Zener Diode
RESOURCES
Title Author ISBN
Aircraft Electricity and Electronics
Eisman 0-02-801859-1
Art of Electronics Horowitz /Hill
Horowitz /Hill
0-521-37095-7
Elements of Electronics
Hickey/ Villines
0070286957
Modern Aviation Electronics
Helfrich 0-13-118803-8
Micro Electronics in Aircraft systems
E Pallet 0-273-08612-X
My Blog CAA UK Recommended Books
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