This document provides an introduction to semiconductor electronics and components used in mechatronics. It discusses the energy bands in conductors, insulators, and semiconductors. Semiconductors like silicon have properties between conductors and insulators due to their valence and conduction bands. Doping semiconductors with elements like boron or phosphorus creates n-type or p-type materials. The document describes pn junctions, diodes, rectifiers, zener diodes, LEDs, photodiodes, and bipolar junction transistors. It provides examples of common semiconductor components and explains their characteristics, symbols, and applications in electronic circuits.

1. MECHATRONICS
SEMICONDUCTOR ELECTRONICS
PUSHPARAJ MANI PATHAK
MECHANICAL & INDUSTRIAL ENGINEEING, IIT ROORKEE
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2. Introduction
• One needs to understand the physical characteristics of
semiconductors, used in electronic circuits.
• We will see the physics of semiconductors, and learn how
electronic components are designed using different types of
semiconductor materials.
• We also learn the circuit schematic symbols for different
semiconductor diodes and transistors, and use the devices in
circuit design.
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3. Energy bands in conductor, insulator, semiconductors
• In materials there are three bands.
• Valence band and conduction
band are separated by forbidden
band.
• In metals large number of weakly
bound electrons in conduction
band are there.
• When voltage is applied to metals,
the electrons migrate freely
producing a current.
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4. Valence and Conduction Bands of Materials
• In conductors, valence
electrons are loosely
bound.
• In insulators valence
electrons are tightly
bound.
• Class of materials,
elements in group IV of
the periodic table, have
properties between
conductors and insulators.
• They are called
semiconductors.
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5. • Elements of group IV of periodic table are silicon and
germanium.
• The properties of pure semiconductor crystals can be
significantly changed by inserting small quantities of elements
from group III or group V of the periodic table into the crystal
lattice of the semiconductor.
• These elements, known as dopants.
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6. • Silicon has four valence electrons.
• If Arsenic or phosphorous of group V is added to the
crystal lattice, one of the five valence electrons in each
dopant atom remains freer to move around.
• The dopant is called a donor.
• The resulting semiconductor is called n-type silicon due
to the electrons available in the crystal lattice as charge
carriers.
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7. • If the silicon is doped with boron or gallium from group III,
holes form due to missing electrons in the lattice where
acceptor dopant atoms have replaced silicon atoms.
• This is because the dopant atom only has three valence
electrons.
• A hole can jump from atom to atom, producing a positive
current.
• This type semi conductor is called p-type.
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8. 8
pn Junction Characteristics
0.6–0.7 V

9. • In forward bias as the applied voltage approaches the value of the contact
potential (0.6–0.7 V for silicon), the current increases exponentially
𝐼𝐷 = 𝐼0 𝑒
𝑞𝑉𝐷
𝑘𝑇 − 1
• where ID is the current through the junction,
• I0 is the reverse saturation current,
• q is the charge of one electron (1.60×10-19 C),
• k is Boltzmann’s constant (1.381×10-23 J/K),
• VD is the forward bias voltage across the junction,
• T is the absolute temperature of the junction in Kelvin
• In case of reverse bias a reverse saturation current (I0 ) does flow, but it is
very small ( of the order of 10-9 to 10-15 A).
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10. Silicon Diode
• A pn junction passes
current in only one
direction.
• It is known as a silicon
diode and is sometimes
referred to as a rectifier.
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11. 11
Examples of Common Diodes
Introduction to Mechatronics: D.G. Alciatore &
Michael B. Histand; Tata Mc Graw Hill, 4th Edition

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13. 13
Ideal, Approximate and Real Diode Curves

14. Half Wave Rectifier Circuit Assuming an Ideal Diode
• When Vi is +ve diode is
reverse bias so behaves as
open circuit thus no current
flows through resistance so
Vo=Vi
• When Vi is –ve, diode is
forward bias equivalent to
short circuit thus no voltage
drops across diode so Vo =0
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15. Ac-to-dc Converter With Full-bridge Rectifier
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16. Full-bridge Rectifier Action
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17. Diode Bridges
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18. ▪ The cylindrical device on the right in the photograph has a
current limit of 1A. Physically, it is 7 mm high, and 10 mm in
diameter.
▪ The flat device on the left has a current limit of 4A. It is has a
thickness of 6 mm, is 16 mm in height, and 19 mm in width.
▪ photograph on the right shows a large, high-power diode
bridge.
▪ It has a current capacity of 15A. The peak reverse-bias voltage
is 400V.
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19. Zener Diode (avalanche, or voltage-regulator diodes)
• Most diode breakdown voltage is 50 V.
• These have steep breakdown curves with well defined
breakdown voltage.
• Thus maintains nearly constant voltage over a wide range of
currents.
• Thus they are good voltage regulators.
• To properly use the zener diode in a circuit, the zener should
be reverse biased with a voltage kept in excess of its
breakdown or zener voltage Vz .
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21. Zener as voltage regulator
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𝐼𝑧 =
𝑉𝑖 − 𝑉
𝑧
𝑅
Using KVL
∆𝐼𝑧=
∆𝑉𝑖 − ∆𝑉
𝑧
𝑅
• This tells how change in current is related to change in voltage.
• The zener diode is a nonlinear circuit element, and therefore Vz is not
directly proportional to Iz

22. • However, it is useful to define a dynamic resistance Rd that is
the slope of the zener characteristic curve at a particular
operating point.
∆𝐼𝑧=
∆𝑉
𝑧
𝑅𝑑
So on substitution we can get
∆𝑉
𝑜 = ∆𝑉
𝑧 =
𝑅𝑑
𝑅𝑑+𝑅
∆𝑉𝑖
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23. Light Emitting Diode
• LED are diodes that
emit photons when
forward bias
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24. Photodiode
• These are designed to detect
photons and can be used in
a circuit to sense light.
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25. Transistors
• Bipolar Junction Transistor
• Field Effect Transistors
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26. Bipolar Junction Transistor
• A bipolar junction transistor (BJT), consists of three adjacent
regions of doped silicon, each of which is connected to an
external lead.
• There are two types of BJTs: npn and pnp transistors
• It consists of a thin region or layer of p-type silicon
sandwiched between two layers of n-type silicon.
• Three leads are connected to the three regions, and they are
called the collector, base, and emitter.
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27. npn Bipolar Junction Transistor
• The n-type
silicon in the
emitter is more
heavily doped
than the
collector
• So the collector
and emitter are
not
interchangeable.
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28. • VCE is the voltage between the collector and emitter,
• VBE is the voltage between the base and emitter.
𝑉𝐵𝐸 = 𝑉𝐵 − 𝑉𝐸
𝑉𝐶𝐸 = 𝑉𝐶 − 𝑉𝐸
𝐼𝐸 = 𝐼𝐵 + 𝐼𝐶
• Normally VC>VB>VE so BE jn forward bias; BC jn is reverse bias
• IB controls IC, acts as current amplifier.
• 𝐼𝐶 = 𝛽𝐼𝐵
• Transistor connections are common base, common emitter and
common collector.
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29. References
• W. Bolton, Mechatronics: Electronic Control Systems in
Mechanical and Electrical Engineering (6th Edition), Pearson,
2015
• D.G. Alciatore and Michael B. Histand, Introduction to
Mechatronics, Tata Mc Graw Hill, 2012.
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Thank You