Unit 19 - Electronics I (Diodes)
Year 12 Physics
Time: 2 weeks
Sem 3 / Term 2
Physics
Unit 19
electronics I
Diodes
Unit 19 - Electronics I (Diodes)
Year 12 Physics
Time: 2 weeks
Sem 3 / Term 2
Lesson Overview
Lesson Date Obj.
1
Description
Definitions, Semiconductor theory
2
Structure & characteristics of Diodes
3
4
Rectification
5
Rectifier Prac
Unit 19 - Electronics I (Diodes)
Year 12 Physics
Lesson 1 - Semiconductors & Defintions
Objectives:
Time: 2 weeks
Sem 3 / Term 2
Unit 19 - Electronics I (Diodes)
Year 12 Physics
Time: 2 weeks
Sem 3 / Term 2
Electronics I - Diodes
Definitions
Semiconductor
Solid State
Vacuum Tube
Hole
Intrinsic Semi Conductor
Doping
n-type and p-type semiconductor
p-n junction
junction diode
biasing
LED (Light Emitting Diode)
Semiconductors are a group of solids in Group IV of the Periodic Table germanium and silicon. These elements have 4 valence electrons, and a
rigid crystal structure, with each atom sharing an electron pair with 4
neighbouring atoms.
This means that no free electrons are available as
current carriers, as they are in conductors.
However, impurities can be
added to the silicon crystal, during its manufacture, which gives rise to a
moderately conducting material. This process is called Doping, producing
either n-type or p-type semiconductors, depending on what impurities are
added.
Unit 19 - Electronics I (Diodes)
Year 12 Physics
Time: 2 weeks
Sem 3 / Term 2
N-TYPE If 5 valent atoms like Arsenic or Antimony are doped into the silicon
in minute quantities, they will bond into the crystal lattice, but only 4 of the 5
valence electrons will be paired, leaving a free electron. This electron is
available to move as a current carrier. If this free electron leaves its parent
atom, it will leave a positive charge behind.
Thus, n-type silicon is still
electrically neutral. This electron-rich silicon is called N-type semiconductor.
P-TYPE If 3 valent atoms like Aluminium, Gallium or Indium are added to
pure silicon as impurities, they will bond into the crystal lattice, by accepting
an electron from 3 neighbouring silicon atoms. The 4th neighbouring atom
has an incomplete electron pair bond. This leaves a hole in the electron pair
where an electron should be. This hole may be thought of as a positive
charge, since it acts as a trap into which free electrons may fall. As an
electron fills this hole, it leaves being another hole. Thus as electrons hop
from hole to hoe, this effectively causes the holes to move in opposite
direction. Thus p-type silicon may conduct by holes moving in one direction.
Unit 19 - Electronics I (Diodes)
Year 12 Physics
Time: 2 weeks
Sem 3 / Term 2
The PN Junction Diode
Out of circuit: If two pieces of p-type
and n-type are joined together, they form
a PN Junction. With a continuous crystal
lattice, the free electrons and holes,
being free to move, will be attracted
towards each other for a brief moment.
When they meet in the middle, they will
annihilate, leaving a number of ions near
the junction.
These ions create an
electric field, halting the movement of
charges near the junction.
In circuit: How do diodes work in circuits?
What relationship is there
between the voltage across a diode, and the current through a diode? We
have investigated this for passive components, so lets look at diodes as well.
Forward Biassing: If the N side is connected to the -ve terminal of a battery,
as in figure 1, electrons from the battery flow into the N-type piece replacing
the electrons which have moved across the junction to fill the holes in the Ptype material. As the holes fill up, electrons move out of the P-type, and
return to the battery. This creates more holes in the P side, which then
migrate towards the junction, to be annihilated and so on...
Thus, current will flow through the device if it is Forward Biassed.
Unit 19 - Electronics I (Diodes)
Year 12 Physics
Time: 2 weeks
Sem 3 / Term 2
Reverse Biassing: If the N side is connected to the +ve terminal of the
battery, the voltage set up across the device attracts the holes in the P side
and the electrons in the N side away from the junction. The junction region is
left without any current carriers. A Depletion Zone is said to be created.
Consequently, no current will flow through the device if it is Reverse Biassed.
By following the path of electron flow in the following circuit diagrams, can
you describe what each circuit does?
Unit 19 - Electronics I (Diodes)
Year 12 Physics
Lesson 2 Objectives:
Time: 2 weeks
Sem 3 / Term 2
Unit 19 - Electronics I (Diodes)
Year 12 Physics
Lesson 3 - Regulation
Objectives:
Time: 2 weeks
Sem 3 / Term 2
Unit 19 - Electronics I (Diodes)
Year 12 Physics
Time: 2 weeks
Sem 3 / Term 2
Regulation
In electronics, regulation is the process by which DC voltage levels and
quality are controlled. In general, two qualities are being controlled; output
voltage level, and ripple.
The simplest form of voltage regulation is to use a parallel capacitor across
the output of a half-wave or full-wave rectifier. The capacitor simply reduces
the ripple on the output voltage, but does no have any effect on the DC value
of the output voltage
Another common form of regulation uses a Zener diode in reverse bias to set
the output voltage. All diodes have a reverse breakdown, or Zener, voltage.
Some special diodes, called Zener diodes, are designed to have very specific
Zener voltages. They can be used to regulate the DC value of the output
voltage, but have no effect on the ripple.
Unit 19 - Electronics I (Diodes)
Year 12 Physics
Time: 2 weeks
Sem 3 / Term 2
Investigation: Rectification
Half-Wave Rectification
Build the following circuit:
Graph the input voltage and output voltage traces on some graph paper, with and without
the capacitor.
 Investigate the effect of different values for the capacitor. How does it effect the output
voltage waveform?
 Investigate the effect of different values for the resistor. How does it effect the output
voltage waveform?
Full-Wave Rectification
Build the following circuit:
Warning: Set the CRO
inputs to AC input.
Graph the input voltage and output voltage traces on some
graph paper, with and without the capacitor.
 Investigate the effect of different values for the capacitor. How does it effect the output
voltage waveform?
 Investigate the effect of different values for the resistor. How does it effect the output
voltage waveform?
Unit 19 - Electronics I (Diodes)
Year 12 Physics
Lesson 4 - Zener Regulation
Objectives:
Time: 2 weeks
Sem 3 / Term 2
Unit 19 - Electronics I (Diodes)
Year 12 Physics
Time: 2 weeks
Sem 3 / Term 2
Investigation – Zener Regulation
Build the following circuit: - 8V peak for source
On graph paper, draw the output voltage across the load resistor.
Q1.
What is the nominal voltage (minimum voltage of the ripple)?
Q2.
What is the ripple voltage (amplitude of the ripple)?
Modify the circuit as follows:
Graph the voltage waveforms across the load resistor and across the buffer resistor.
Q3.
How does the voltage across the load resistor compare with the load resistor form
the previous circuit?
Q4.
What is the main advantage in using zener regulation?
Build the circuit on a breadboard, and compare the real circuit with the computer
simulation.
(i.e. make notes, draw graphs etc)
Unit 19 - Electronics I (Diodes)
Year 12 Physics
Lesson 5 Objectives:
Time: 2 weeks
Sem 3 / Term 2
Unit 19 - Electronics I (Diodes)
Year 12 Physics
Lesson 6 Objectives:
Time: 2 weeks
Sem 3 / Term 2