2. • is a component of an electrical circuit that resists the
flow of electrical current. A resistor has two terminals
across which electricity must pass, and is designed to
drop the voltage of the current as it flows from one
terminal to the next. A resistor is primarily used to create
and maintain a known safe current within an electrical
component.
• Resistance is measured in ohms, after Ohm's law. This
rule states that electrical resistance is equal to the drop in
voltage across the terminals of the resistor divided by the
current being applied to the resistor.
• NO RESISTOR, LARGE FLOW OF CURRENT
3. • An ohmmeter is
an electrical instrument that
measures electrical resistance,
the opposition to an electric
current. Micro-ohmmeters
(microhmmeter or
microohmmeter) make low
resistance measurements.
Megohmmeters (aka
megaohmmeter or in the case
of a trademarked
device Megger) measure large
values of resistance. The unit
of measurement for resistance
is ohms (Ω).
4. • Resistors are used with transducers to
make sensor subsystems. Transducers are
electronic components which convert energy
from one form into another, where one of the
forms of energy is electrical. A light dependent
resistor or LDR is an example of an input
transducer. Changes in the brightness of the
light shining onto the surface of the LDR result in
changes in its resistance. As will be explained
later, an input transducer is most often
connected along with a resistor to make a circuit
called a potential divider. In this case, the
output of the potential divider will be a voltage
signal which reflects changes in illumination.
5. • Resistors are used for
regulating current and they
resist the current flow and the
extent to which they do this is
measured in ohms (Ω).
Resistors are found in almost
every electronic circuit. The
most common type of resistor
consists of a small ceramic
(clay) tube covered partially by
a conducting carbon film. The
composition of the carbon
determines how much current
can pass through.
RESISTOR IN CIRCUIT = SMALLER FLOW OF
CURRENT
6.
7. • A carbon film is deposited on an insulating substrate, and
a helix cut in it to create a long, narrow resistive path.
Varying shapes, coupled with the resistivity of amorphous
carbon, can provide a variety of resistances. Carbon film
resistors feature a power rating range of 0.125 W to 5 W
at 70 °C. Resistances available range from 1 ohm to 10
meg ohm.
8. • Wire wound resistors are made by winding thin wire onto
a ceramic rod. They can be made extremely accurately
for use in multimeters, oscilloscopes and other
measuring equipment. Some types of wire wound
resistors can pass large currents without overheating and
are used in power supplies and other high current
circuits.
9. • Thin film resistors are made
by sputtering (a method of vacuum
deposition) the resistive material onto
an insulating substrate. The film is then
etched in a similar manner to the old
(subtractive) process for making
printed circuit boards; that is, the
surface is coated with a photo-
sensitive material, then covered by a
pattern film, irradiated
with ultraviolet light, and then the
exposed photo-sensitive coating is
developed, and underlying thin film is
etched away.
• Thick film resistors are manufactured
using screen and stencil printing
processes
10. • A common type of axial resistor today is
referred to as a metal-film resistor.
Metal electrode leadless face resistors
(MELF) often use the same technology,
but are a cylindrically shaped resistor
designed for surface mounting. Metal
film resistors are usually coated with
nickel chromium (NiCr), but might be
coated with any of the cermet materials
listed above for thin film resistors.
Unlike thin film resistors, the material
may be applied using different
techniques than sputtering (though that
is one such technique). Also, unlike
thin-film resistors, the resistance value
is determined by cutting a helix through
the coating rather than by etching (this
is similar to the way carbon resistors
are made.)
11. • Metal-oxide film resistors are made
of metal oxides such as tin oxide.
This results in a higher operating
temperature and greater
stability/reliability than Metal film.
They are used in applications with
high endurance demands.
12. • The primary resistance element of a
foil resistor is a special alloy foil
several micrometres thick. Since
their introduction in the 1960s, foil
resistors have had the best
precision and stability of any resistor
available. One of the important
parameters influencing stability is
the temperature coefficient of
resistance (TCR). The TCR of foil
resistors is extremely low, and has
been further improved over the
years.
13. • An ammeter shunt is a special type of
current-sensing resistor, having four
terminals and a value in milliohms or
even micro-ohms. Current-measuring
instruments, by themselves, can usually
accept only limited currents. To
measure high currents, the current
passes through the shunt, where the
voltage drop is measured and
interpreted as current. A typical shunt
consists of two solid metal blocks,
sometimes brass, mounted on to an
insulating base. Between the blocks,
and soldered or brazed to them, are
one or more strips of low temperature
coefficient of
resistance (TCR) manganin alloy.
14. • In heavy-duty industrial high-current
applications, a grid resistor is a large
convection-cooled lattice of stamped
metal alloy strips connected in rows
between two electrodes. Such industrial
grade resistors can be as large as a
refrigerator; some designs can handle
over 500 amperes of current, with a
range of resistances extending lower
than 0.04 ohms. They are used in
applications such as dynamic
braking and load
banking for locomotives and trams,
neutral grounding for industrial AC
distribution, control loads for cranes
and heavy equipment, load testing of
generators and harmonic filtering for
electric substations.[
15.
16.
17. • Resistors are too small to have numbers printed on them
and so they are marked with a number of colored bands.
Each color stands for a number. Three color bands
shows the resistors value in ohms and the fourth shows
tolerance. Resistors can never be made to a precise
value and the tolerance band (the fourth band) tells us,
using a percentage, how close the resistor is to its coded
value.
RESISTOR’S VALUE TOLERANCE
18. • The first band on a resistor is interpreted as the FIRST
DIGIT of the resistor value. For the resistor shown below,
the first band is yellow, so the first digit is 4
• The second band gives the SECOND DIGIT. This is a violet band,
making the second digit 7. The third band is called the MULTIPLIER
and is not interpreted in quite the same way. The multiplier tells you
how many noughts you should write after the digits you already have.
A red band tells you to add 2 noughts. The value of this resistor is
therefore 4 7 0 0 ohms, that is, 4 700 , or 4.7 . Work through this
example again to confirm that you understand how to apply the
colour code given by the first three bands.
• The remaining band is called the TOLERANCE band. This indicates
the percentage accuracy of the resistor value. Most carbon film
resistors have a gold-coloured tolerance band, indicating that the
actual resistance value is with + or - 5% of the nominal value.
19.
20. • Real resistor values (the E6 and E12 series)
• To produce a sensible range of resistor values you need to increase the
size of the 'step' as the value increases. The standard resistor values are
based on this idea and they form a series which follows the same pattern
for every multiple of ten.
• The E6 series (6 values for each multiple of ten, for resistors with 20%
tolerance)
10, 15, 22, 33, 47, 68, ... then it continues 100, 150, 220, 330, 470, 680,
1000 etc.
Notice how the step size increases as the value increases. For this series
the step (to the next value) is roughly half the value.
• The E12 series (12 values for each multiple of ten, for resistors with 10%
tolerance)
10, 12, 15, 18, 22, 27, 33, 39, 47, 56, 68, 82, ... then it continues 100,
120, 150 etc.
Notice how this is the E6 series with an extra value in the gaps.
• The E12 series is the one most frequently used for resistors. It allows you
to choose a value within 10% of the precise value you need. This is
sufficiently accurate for almost all projects and it is sensible because most
resistors are only accurate to ±10% (called their 'tolerance'). For example
a resistor marked 390 could vary by ±10% × 390 = ±39, so it could be any
value between 351 and 429.
21.
22. • When current flows through a resistance, electrical energy is
converted into heat. This is obvious in an electric torch where
the lamp filament heats up and glows white hot. Although the
result may be less evident or imperceptible, exactly the same
process of energy conversion goes on when current flows
through any electronic component.
• The power output of a lamp, resistor, or other component, is
defined as the rate of change of electrical energy to heat, light,
or some other form of energy. Power is measured in watts, W,
or milliwatts, mW, and can be calculated from:
P= VI
where P is power.
• What is the power output of a resistor when the voltage across it
is 6 V, and the current flowing through it is 100 mA?
0.6 W of heat are generated in this resistor. To prevent
overheating, it must be possible for heat to be lost, or dissipated,
to the surroundings at the same rate
23. • A resistor's ability to lose heat depends to a large extent
upon its surface area. A small resistor with a limited
surface area cannot dissipate (=lose) heat quickly and is
likely to overheat if large currents are passed. Larger
resistors dissipate heat more effectively.
Resistors of different sizes
24. • The standard size of carbon film resistor used in most
circuits has a power rating of 0.5 W. This means that a
resistor of this size can lose heat at a maximum rate of
0.5 W. Some resistors are designed to pass very large
currents and are cased in aluminum with fins to increase
surface area and promote heat loss.
• Input and signal processing subsystems in electronic
circuits rarely involve large currents, but power rating
should be considered when circuits drive output
transducers, such as lamps, LEDs, and loudspeakers.
25.
26. Thank you for listening!
Presented by: Lorenz Alfuente, Emmanuel Mestidio and JP Alegario
Credits to:
http://www.doctronics.co.uk/resistor.htm
http://en.wikipedia.org/wiki/Resistor
http://www.kpsec.freeuk.com/components/resist.htm
http://www.wisegeek.com/what-is-a-resistor.htm
http://www.technologystudent.com/elec1/resist1.htm
