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Diodes

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Diodes
I. Pre-viewing tasks
1. Look through the words and expressions given below and guess what this film can be
about. Write down several sentences expressing your viewpoint on possible contents of the
film.
P-N junction ++
Semiconductor ---
electrons +++
Holes +++
Impurities ---
Bias ++
direct current ---
alternating current ---
Resistance +++
Capacitance +++
2. Write down types of diodes that will be mentioned in the film.
Photodiodes, Light Emitting Diode (LED), Laser diode
3. Watch the film and make sure that the choice you made is correct.
II. While-watching-the-film tasks
a). Watch the film "Diodes" and mark the following sentences as true or false.
1. Photodiodes are used in road signals. --2. Laser diodes are used in security alarms. +++
3. The cathode acts as a positive terminal. +++
4. The depletion region contains only positive ions on the P-side and negative ions on the
N-side of the junction. --5. The motion of electrons doesn't stop immediately after the formation of the depletion
region. +++
6. Junction potential is 0.6 V for germanium and 0.2 V for silicon. ---
7. If a diode is operated in the forward-bias mode, we connect the positive terminal of
the battery to the anode and the negative terminal to the cathode of a P-N junction diode.
+++
8. In the reverse bias case the majority charge carriers cross the depletion region setting
up the current flow. +++
9. When the diode is operated in DC voltage, the resistance of the diode is called dynamic
resistance. --10. Resistance takes a very high value of Mega Ohms during reverse bias. +++
b). Watch the film again and answer the following questions.
1. Who and when coined the term diode? What is the origin of the word diode?
William Henry Eccles was the first who coined the term diode, in 1919.
Origin of the word diode from the Greek roots di, meaning “two”, and ode, meaning
“electrode”.
2. What material is used to form the p-n junction?
Silicon and germanium
3. What impurities are used if we want to get semiconductors of N-type and P-type?
P-type:
Borum atom
N-type:
Phophorus Atom
4. What is diffusion?
Electrons from the N-side get attracted to the holes of the P-side, these electrons cross
over the junction recombine with the holes and sees to be free carriers, this process
called diffusion
5. What is junction potential?
Charged ions level up electric fields in the depletion region known as Junction potential
6. What process is called biasing?
Biasing – process of applying external voltage to an electronic device or a system to
establish suitable working conditions
7. How can you define a drift current and a leakage current?
-electrones move from anode to cathode, setting up the flow of current from anode to
cathode, this current called as a drift current.
- the current that the diode will leak when a reverse voltage is applied to it is called
leakage current
8. What is breakdown voltage?
Breakdown voltage is a parameter that defines the largest reverse voltage that can be
applied to a diode without damaging the material.
9. How does a Zener diode work?
Zener diode- is a diode that permits current to flow in either a forward or reverse
direction. It has heavily doped p-n junction.
10. What is Diffusion capacitance? What is Transition capacitance?
Diffusion capacitance is defined as a change in charge due to change in voltage during
forward bias operation of a diode
Transition capacitance is defined as a change in charge due to change in voltage during
reverse bias operation of a diode
c) Complete the sentences with the correct ending.
1. P-N junction diodes act as a base for all these diodes (LED, photodiodes, laser diodes)
2. The boron atom, being trivalent, accepts one electron from a neighboring silicon
atom and creates vacancy or hole in the silicon structure.
3. As the phosphorus atom donates one electron, it loses its neutrality and becomes
positively charged immobile ion.
4. As electrons cross the junction, they get repelled by the negative ions of the P-side .
5. Diodes are operated in two modes: Forward bias and Reverse Bias.
6. If a diode is operated in the reverse-bias mode, we apply the positive end of the battery
to an Anode and the negative end of the battery to a cathode of the p-n junction diode .
7. In order to prevent a diode from breaking down, a diode should be doped in a very
controlled manner.
8. Zener diodes find many applications in voltage regulated circuits.
9. We select diodes according to their specifications such as DC resistance, AC resistance,
Diffusion capacitance, Transition capacitance.
10. Static resistance plays a vital role in the analysis of Clipping circuits or Rectifier circuits.
III. Post-viewing tasks
Below you will find a mind map that can be used while delivering an introductory lecture
on diodes.
a) Extend this mind map. Write down key words and expressions for each heading. Make
up sentences using these words and expressions.
b) Use your notes to summarize the video in 200 words.
Origin of the
word diode
Applications of
diode
Construction
of P-N
junction diode
Diodes
Zener diode
Parameters of
diode
Biasing of
diode
A)
Origin of the word diode
William Henry Eccles, in 1919
Diode from Greek roots : di+ode( di mean two, ode mean electrode)
Application of a diode
As switch or in rectifiers
Construction of P-N junction diode
Semiconductor device formed by doping the P and N-type semiconductors into silicon or
germanium semiconductors.
Biasing of Diode
When in forward bias its equivalent resistance increases to few Ohms
When in reverse bias its equivalent resistance increases to few Mega Ohms, no current
Parameters of diode
Capacitances:
-diffusion capacitance (during forward bias)
-transition capacitance (during reverse bias)
Zener diode
Zener diode is a heavily doped p-n junction diode, which is used for its current
conduction in reverse bias method and control breakdown voltage
B) This video is about diodes, types of diodes and how they work. Term “diode” was
coined in 1919 by William Henry Eccles. Origin of the word diode from the Greek roots
di, meaning “two”, and ode, meaning “electrode”.
This video tells us about 3 types of diodes: photodiodes, Light Emitting diode (LED),
Laser diodes. LED’s are used in road signals, Laser diodes are used in security alarms,
photodiodes are used in smoke detectors. All these diodes make up p-n junction diodes.
P-n junction diode consists of P-type semiconductor and N-type semiconductor. Boron
atoms are used to get P-type semiconductor and Phosphorus atoms are used to get Ntype semiconductor.
Also video tells us about biasing. Biasing – process of applying external voltage to an
electronic device or a system to establish suitable working conditions. There are 2 types
of current: leakage current and drift current. Electrons move from anode to cathode,
setting up the flow of current from anode to cathode, this current called as a drift
current. The current that the diode will leak when a reverse voltage is applied to it is
called leakage current. Breakdown voltage is a parameter that defines the largest
reverse voltage that can be applied to a diode without damaging the material. Zener
diode is a diode that permits current to flow in either a forward or reverse direction. It
has heavily doped p-n junction.
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