Class notes
Electrical Engineering Semester 2 notes
- Institution
- University Of Cape Town (UCT)
This document includes all the lecture notes from the whole semester.
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W2 Electronic FundamentalsWhy Analogue Electronics?
- electronic systems with a continuously varying signal (in contrast to digital
electronics where signals usually take two levels (discrete)
- ‘analogue’ describes proportional relationship between signal and a
voltage or current that represents the signal
- an understanding of analogue electronics is important and essential when
designing an electronic interface to the physical world (e.g., an
analogue-to-digital converter (ADC)
- some technologies develop rapidly such as wireless communications
technologies
- many rapid advances have been enabled through the refinement of
semiconductors allowing billions of transistors to occupy single ICs
Resistors
Resistors are devices that obey Ohms law: V=IR
,Resistance:
Resistors come in standard values called the E12 and E24 series. The E12
series consists of multiples of the following values: 1, 1.2, 1.5, 1.8, 2.2, 2.7,
3.3, 3.9, 4.7, 5.6, 6.8, 8.2.
Tolerance:
The maximum deviation of the value of the resistor from its specified
value. Commonly available in 1% and 5% tolerances.
Power Dissipation:
Through-hole resistors are commonly available in power ratings of
0.25W, 0.5 W, 1 W, 2 W and 5 W. Most resistors can operate above 100
degrees C, meaning they can burn through breadboards.
Temperature Coefficient:
Any conductor’s resistance will change as its temperature changes.
This is called the Temperature Coefficient of Resistance (TCR) and is
different for different types of resistors.
Maximum Current:
Power dissipation is one factor which limits the maximum current, but
not the only factor. Short bursts of very high current can lead to a
resistor failing.
Maximum Voltage:
If the voltage placed across a resistor is too high there is a possibility
that it will spark across the resistor, or across one of the etched gaps in
the resistive film.
,Resistor Parasitics
▪ All resistors suffer from parasitic capacitance between parallel conductors,
and parasitic inductance. Some resistors are better than others.
▪ Normal through hole resistors are spirals of film around a ceramic rod, and
this give relatively high inductance.
▪ At radio frequencies (RF) the physical size of the resistor becomes
important, with physically smaller resistors typically giving more ideal
performance.
Reading a
Resistor
Through-hole
- Typically come with their values
indicated through the use of colour
bands
- There are either 4 or 5 bands
- Typically the tolerance band is on the
raised portion while the value bands
are in the middle
, Surface Mount (SMD)
- SMD or surface mount (device)
resistors do not have colour
bands, instead they have
numbers printed directly onto
them.
- The standard 3 and 4 digit code
does not give us a way to
determine the SMD resistor’s
tolerance.
- In most cases, however, SMD
resistors marked with a 3-digit
code has a tolerance of 5%,
one with a 4-digit code has a tolerance of 1%.
Potentiometers
- adjustable resistor dividers
Internally they have a resistive
track and a “wiper” that moves
along the track as the
potentiometer is adjusted.
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