EC3011 : Introduction to Electronics and Instrumentation
Introduction & Applications of Diodes
M. Barathraj
Department of Electrical and Electronic Engineering
Faculty of Engineering
University of Jaffna
Thanks to: Dr. S. Thananjeyan
EC3011 - Introduction to Electronics and Instrumentation
• Academic Credits : 03
: M. Barathraj & R. Yesindan
• Lecturers
• Coordinator
: Dr. T. Mukunthan
• 36 hrs Lectures + 15 hrs Laboratory + 6 hrs Assignments + 4 hrs Tutorial
• Contact hours: 3 hours of lectures each week and scheduled lab hours
• Consultations: Lecture notes and tutorial questions are available in the Microsoft
teams. Students are encouraged to ask questions in class, via Microsoft teams and
during tutorial hours.
Indented Learning Outcomes
By the end of this course unit, students should be able to
• Demonstrate applications of diodes in electronic circuits.
• Explain behaviors of Biasing circuits, small signal models of an BJT
amplifier circuit.
• Design simple op amp and BJT circuits.
• Analyze RC and RL circuits and its step response
• Demonstrate data acquisition systems and actuator systems
Syllabus Outline
1. Applications of Diodes
2. BJTs and MOSFETs
3. Operational Amplifier
4. RC, RL Circuit Transient Behavior
5. Data Acquisition (DAQ)
6. Introduction to Motor Control
Assessment:
Assessment Type
In-Course
Assessment
End of Course
Evaluation
Assessment Method
Percentage(%)
Assignment
15
Lab Report / Field Report
20
Mid Semester Assessment
15
End Semester Examination
50
General Instructions
• Attendance for lectures should be greater than 80%.
• Attendance for labs should be 100%.
• Academic dishonesty including plagiarism will result in disciplinary action.
• Instructors will be present during the labs.
• Students are requested to follow the safety instruction in the Laboratory and
risk assessments for each lab session
Applications of Diodes
• Revision of p-n junction
• I-V characteristics
• Half wave and full wave rectifiers
• Diode clamper and limiter circuits
• Zener diodes, regulators, protection circuits
• logic gate, voltage multipliers, photovoltaics and photo diodes.
Diodes
Revision of p-n junction
• Simple electronic circuit elements can be divided into two fundamental
groups by their terminal characteristics:
• Linear devices – devices that can be described by linear algebraic equations or linear
differential equations;
• Non-linear devices – those devices that are described by non-linear equations.
• Resistors, capacitors, and inductors are examples of passive circuit elements
that are basically linear elements
• The diode is the most basic of the non-linear electronic circuit elements.
• It is a simple two-terminal device: a tube with two electrodes (di - two; ode - path), the
anode and the cathode
Ideal diode
• An ideal diode is a true one-way electronic device, that is, a device that
provides zero resistance to current flowing in one direction, but infinite
resistance to current flowing the opposite direction.
A - the anode (Greek, ana up C hodos way)
K - the cathode (Greek, kata down C hodos way).
❖ It is important to notice that the definition of the sign convention
Analytically the transfer relationship can be described as:
𝐼 = 0 𝑓𝑜𝑟 𝑉 < 0
𝑉 = 0 𝑓𝑜𝑟 𝐼 ≥ 0
Passive Sign Convention
• It is important to notice that the definition of the sign convention is extremely
important.
• For many devices that are linear (for example, a resistor), reversing the
polarity of both the voltage and current yields the same V-I relationship
(Ohm’s Law) as long as the passive sign convention is followed.
• Reversing the polarity of the voltage and current (still keeping the passive sign
convention) can yield, in general, a drastically different V-I relationship for a
non-linear devices: thus the sign convention takes special significance.
The passive sign convention allows consistent equations to be written to characterize electronic devices. In two terminal
devices, it simply states that, when describing the device, positive reference current enters the positive voltage reference
node and exits the negative voltage node.
Functional relationships of an ideal diode
• The functional relationships of an ideal diode are a piece-wise linearization of
the V-I transfer relationship and lead to two piece-wise linear models that are
often used to replace a diode for analysis purposes
• a short circuit when the applied current is positive, and
• an open circuit when the applied voltage is negative.
Question
• For the simple ideal diode circuit shown, determine the current in the diode
if:
a) 𝑉𝑆 = 1𝑉
b) 𝑉𝑆 = −1𝑉
Semiconductor Diode Volt-Ampere Relationship
• Semiconductor Diodes are formed with the creation of a p-n junction.
• This junction is a transition region between a semiconductor region that has
been injected (doped) with acceptor atoms (a p-region) and one that has
been injected with donor atoms (an n-region)
• The p-region becomes the anode of a semiconductor diode.
• The n-region becomes the cathode of a semiconductor diode.
Semiconductor Diodes
• Semiconductor diodes are real diodes that have the following differences
compared to the ideal diodes
• In the non-conducting region (when the p-n junction is reverse biased) the diode
current is not exactly zero: the diode exhibits a small reverse leakage current.
• The diode requires a small positive voltage to be applied before it enters the
conducting region (when the p-n junction is forward biased). When in the
conducting region the diode has a non-zero dynamic resistance.
• For large input voltages and/or currents the diode enters breakdown regions. In
the forward direction, power dissipation restrictions leads to thermal destruction
of the diode. In the reverse direction, the diode will first enter a Zener region of
conduction then thermal destruction.
• The differences mean circuit designers and engineers must be careful to
avoid an oversimplification of the analysis of diode circuitry.
Mode of Operation
Mode of Operation
Types of Diodes
Types of Diodes
Types of Diodes
Types of Diodes
Types of Diodes
V-I relationship of a Diode
• In the region near the origin of the V-I relationship for a semiconductor
diode, the V-I curve can be described analytically by two equivalent
expressions
𝐼 = 𝐼𝑠 𝑒
or
𝚐𝑉
𝜂𝑘𝑇
− 1 = 𝐼𝑠(𝑒
𝑉
𝜂 𝑉𝑡
− 1)
𝐼
𝑉 = 𝜂 𝑉𝑡 ln( + 1)
𝐼𝑠
• 𝑉 = voltage equivalent temperature of the diode =
𝑡
26 𝑚𝑉 @ 𝑟𝑜𝑜𝑚 𝑡𝑒𝑚𝑝𝑒𝑟𝑎𝑡𝑢𝑟𝑒 ≈ 300 𝐾
𝑘𝑇
𝑞
𝑇 ≈ 11600 ≈
Dynamic resistance
• Dynamic resistance is defined as the incremental change in voltage with
respect to an incremental change in current.
• For the diode the dynamic resistance is given by
𝑉
𝜕𝑉
𝜂 𝑉𝑡
𝜂 𝑉𝑡 −𝜂 𝑉
𝑡
𝑟𝑑 =
=
=
𝑒
𝜕𝐼 𝐼𝑠 + 𝐼
𝐼𝑠
• In the strongly forward-biased and strongly reversed-biased regions the
dynamic resistance is then:
• 𝑟𝑑 ≈ 0, 𝑤ℎ𝑒𝑛 𝑉 ≫ 𝑉𝑡 or equalantly I ≫ IS (strongly forward biased) AND
• 𝑟𝑑 ≈ ∝, 𝑤ℎ𝑒𝑛 𝑉 ≪ 𝑉𝑡 or equalantly I ≈ IS (strongly reverse biased)
V-I Plot
• A plot of the V-I relationship for a typical diode with 𝐼𝑆 = 1 𝑛𝐴 and μ =
1 & 2 at a temperature of 300K appears as in this figure
I-V Curve
V-I Plot
• Notice that the basic shape of this relationship is similar to that of the ideal
diode with the following exceptions
• In the reverse-biased region, the current is not exactly zero, it is instead a small leakage
value, 𝐼𝑆.
• The forward-biased region exhibits real, non-zero resistance.
• The vertical portion of the curve is displaced to the right.
• There appears to be a voltage at which the diode begins to conduct.
• This voltage is often called a threshold voltage which for silicon diodes lies in the range
of 0.6 V to 0.9 V
Question
• The saturation current of a Si diode is 2.0 𝑛𝐴 and the empirical scaling
constant,𝜂 = 2. Calculate the following
a) At room temperature (300 K) the diode current for the following voltages.
-5 V, -1 V, 0.5 V, 0.9 V
A simple diode circuit
• Kirchhoff ’s Voltage Law taken around the closed loop yields
𝑉 − 𝐼𝑅 − 𝑉𝑑 = 0
which leads to non-linear equation
𝐼
𝑉 − 𝐼𝑅 − 𝜂 𝑉𝑡 ln( + 1) = 0
𝐼𝑠
that must be solved for 𝐼
Diode Application
➢ Diode is two terminal electrical device allowing current to
move through it in one direction.
➢ Used to control the direction of current
➢ Rectification :-convert alternating current to direct current
Rectifier
Rectifier
Half Wave Rectifier
Rectifier
Full Wave Rectifier
Reverse Current Protection
Problem
Solution
Diode Circuits
▪ Half-wave rectifier
▪ Full-wave rectifier
▪ Clipper Circuit
▪ Clamper Circuit
▪ Peak Detector
▪ Envelope Detector
▪ Voltage Multiplier
▪ Regulator
▪ Diode Logic Gates
Questions & Discussion ?
THANK YOU!
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