RESISTOR

CARBON COMPOSITE RESISTOR

VARIABLE RESISTOR
PHOTORESISTOR

GROUP 2:
APILAN, MARY MAE
OLAYVAR, RICALYN O.
CARBON COMPOSITE
RESISTOR • A fixed-value resistor made of
carbon composition is used to
limit or control the flow of
electric current. It consists of
a solid cylindrical resistive
element with attached wire
leads or metal end caps. The
resistor is composed of carbon
powder and graphite.
KEY CHARACTERSITICS:
• High Pulse Handling: Carbon composite resistors can absorb and dissipate
large energy pulses, making them suitable for circuits exposed to high surge
conditions.
• Non-Linear Behavior: Their resistance can vary with temperature, voltage,
and aging, leading to non-linear performance. This can be a drawback in
precision circuits.
• Wide Tolerance Range: They generally have a broad tolerance range (±5%
to ±20%), meaning their actual resistance can deviate significantly from the
nominal value.
• High Noise: These resistors can generate more electrical noise compared to
other resistor types, which can be problematic in low-noise applications.
 APPLICATIONS:
• High-Energy Circuits: Due to their pulse-handling capability, carbon
composite resistors are used in applications such as surge protectors, RF
circuits, and high-voltage power supplies.
• Vintage and Restoration Projects: They are often used in the restoration
of vintage electronics to maintain the original characteristics of the circuit.
• Safety and Testing Equipment: In some cases, they are used in safety
circuits and testing equipment where high pulse absorption is necessary.
 LIMITATIONS:
•Decreasing Usage: The development of more stable, reliable, and
precise resistors like metal film and carbon film resistors has led to a
decline in the use of carbon composite resistors.
•Environmental Sensitivity: Their performance can degrade over
time and under extreme environmental conditions, making them less
ideal for long-term use in critical applications.
 VARIABLE RESISTOR
• A variable resistor is a passive component in electrical and electronic circuits
that allows for adjustable resistance. It functions as a resistor with a
mechanism to change its resistance, enabling control of the electric current in
the circuit.
 Types of Variable Resistor
•Potentiometer:
A three-terminal resistor with a sliding or rotating contact that acts as
an adjustable voltage divider. It is the most common type of variable
resistor, used to produce a voltage output based on its position.
Typical applications include volume controls in audio equipment,
tuning circuits, and adjustable power supplies.
•Rheostat:
A two-terminal potentiometer used to vary resistance and control
current. It is commonly found in light dimmers, motor speed controls,
and heater controls.
• Trimpot (Trimmer • Digital Potentiometer (Digital
Potentiometer): Pot):
A small potentiometer used for fine-tuning and An electronically controlled potentiometer used
calibration in circuits, typically adjusted with a in digital circuits. It is common in digital volume
small screwdriver. It is used for instrument controls, automatic gain control, and
calibration, setting amplifier bias, and adjusting programmable filters
sensor sensitivity.
• Slider Potentiometer: • Multiturn Potentiometer:
A potentiometer adjusted by sliding A potentiometer that requires multiple
a contact along a track instead of turns of the knob to adjust resistance,
rotating a knob. It is frequently used providing precise control. It is ideal for
in audio mixing consoles, equalizers, applications requiring fine adjustments,
and other audio equipment. such as lab instruments and
measurement devices.
Circuit Symbols of a Variable
Resistor
FUNCTION:
∙ The resistance of a variable resistor changes by altering its length.
Adjusting the length of the resistive element changes the resistance.
∙ A variable resistor has a long resistive strip and a movable part called a
wiper. Moving the wiper along the strip changes the resistance.
 How to Calculate Resistance of Variable Resistor?

R1 = Between ‘x’ and ‘y’

Ɩ = Total length of the element
Ɩ1 = Distance between the wiper and the end ‘y’ of the
element

Example:
R1 = 100 Ω, l = 10 m, l1 = 4 m.
 APPLICATION OF VARIABLE RESISTORS
• Current Control in Circuits:
Variable resistors, often acting as
potentiometers, adjust the current flow in
electronic circuits, particularly in audio
devices. Logarithmic resistors are favored
over linear types for their better alignment
with human loudness perception.
• Fan Speed Adjustment:
These resistors are used in fan speed
controllers to regulate the fan's rotational
speed.

• Light Intensity Modulation:

They are applied in dimmer switches to
modify the brightness of lighting fixtures.
• Voltage and Current Regulation in Power
Supplies: Variable resistors help manage and
stabilize the output voltage and current in power
supply systems.
• Audio Control: Utilized in audio systems to
fine-tune the volume, bass, and tone of sound output.
• Calibration Devices and Sensors: Used for fine
calibration of various instruments and sensors.
• Television Adjustments: Employed to adjust the
color, brightness, contrast, and position of the picture
on television screens.
• Motor Control: Used to control the speed, torque,
and direction of motors, servos, fans, and pumps.
 ADVANTAGES:
• Precision Control: They allow for precise adjustments in a circuit, which is
crucial for calibration and fine-tuning.
• Versatility: Can be used in a wide range of applications, from simple
adjustments to complex tuning tasks in electronic circuits.
• Ease of Use: Variable resistors are user-friendly, typically requiring simple
manual adjustments to change resistance.
 LIMITATIONS:
• Wear and Tear: Over time, the moving parts of a variable resistor
can wear out, leading to degradation in performance.
• Limited Power Handling: They generally have lower power ratings
compared to fixed resistors, which limits their use in high-power
applications.
• Size: Some variable resistors, especially those with large adjustment
ranges or high power ratings, can be physically large, which may not
be suitable for compact circuit designs.
 PHOTORESISTOR
• The name "photoresistor" is derived from
combining the words "photon," which refers to
light particles, and "resistor."
• A photoresistor is a resistor that decreases in
resistance as the intensity of light increases.
• Photoresistors are made from high-resistance
semiconductors like silicon or germanium. They
can also be made from materials such as cadmium
sulfide or cadmium selenide.
• It is sometimes referred to as an LDR (Light
Dependent Resistor), semiconductor
photoresistor, photoconductor, or photocell.
How photoresistor works? • When light hits the photoresistor, some
valence electrons absorb energy from the
light, causing them to break their bonds with
the atoms. These electrons, once freed from
their atomic bonds, are known as free
electrons.

• Electrons in the conduction

band are not associated with
any specific atom, allowing
them to move freely from one
place to another. These freely
moving electrons are known as
free electrons.
• When a valence electron leaves an atom, it creates a vacancy at the
location from which it departed. This vacancy is known as a hole. As a
result, free electrons and holes are generated in pairs.

• In the absence of light,

photoresistors act as
high-resistance
materials, while in the
presence of light, they
act as low-resistance
materials.
 Types of Photoresistors
•Intrinsic Photoresistor:
An intrinsic photoresistor uses a photoconductive material that is
not doped with any impurities. In this case, charge carriers are
excited from the valence band to the conduction band purely due
to light exposure. Intrinsic photoresistors are less sensitive to
the light. Therefore, they are not reliable for the practical
applications.
•Extrinsic Photoresistor:
Extrinsic photoresistors are made from semiconductor materials that are
doped with impurities to enhance efficiency. The dopants used are
shallow and do not ionize in the presence of light. In these
photoresistors, charge carriers are excited between the dopant and the
valence or conduction band. The resistance of an extrinsic
photoresistor decreases quickly with a slight increase in applied
light energy, making extrinsic photoresistors dependable for
practical applications.
 KEY CHARACTERSITICS:
• Light Sensitivity: The resistance of a photoresistor changes based on the amount of
light it receives. In darkness, its resistance is high, and in bright light, its resistance
drops significantly.
• Material: Photoresistors are typically made from semiconductor materials such as
cadmium sulfide (CdS) or cadmium selenide (CdSe), which have properties that change
when exposed to light.
• Response Time: Photoresistors have a slower response time compared to other light
sensors like photodiodes or phototransistors, which may limit their use in applications
requiring rapid changes in light detection.
• Non-Linear Behavior: The change in resistance with light is not linear, meaning the
relationship between light intensity and resistance follows a curve rather than a straight
line.
 APPLICATION:
• Automatic Lighting: Photoresistors are commonly used in outdoor lighting systems that
turn on at dusk and off at dawn based on ambient light levels.
• Light Meters: Used in photographic light meters to measure the intensity of light and help
adjust camera settings.
• Burglar Alarms: Photoresistors can be used in security systems to detect changes in light
levels, triggering alarms when a change indicates potential intrusion.
• Ambient Light Detection: In devices like smartphones, tablets, and laptops, photoresistors
help adjust screen brightness based on the surrounding light conditions, improving user
comfort and conserving battery life.
• Optical Encoders: Photoresistors can be part of optical encoders used to determine the
position of rotating objects by detecting light passing through a slotted disk.
 ADVANTAGES
• Simple Operation: Photoresistors are easy to use and integrate into circuits, making them
a popular choice for light-sensing applications.

• Cost-Effective: They are relatively inexpensive compared to other light sensors, making
them ideal for low-cost applications.

• Wide Range of Light Detection: Photoresistors can detect a wide range of light
intensities, from very low to very high, making them versatile in various applications.
 LIMITATIONS:
• Slow Response Time: Due to their slower response time, photoresistors are not
suitable for applications that require quick light detection or fast switching.

• Temperature Sensitivity: Their resistance can be affected by temperature changes,

which may cause inaccuracies in some applications.

• Environmental Concerns: Some photoresistors use materials like cadmium, which

are hazardous and subject to environmental regulations, limiting their use in certain
applications.
THANK YOU!!
References:
• Photoresistor
https://physics-and-radio-electronics.com/electronic-devices-and-circuits/passive-components/resistors/photo
resistor.html
https://youtu.be/u9Riurh4y9U?si=aVoS3otxh7pGIBSf

• Carbon Composite Resistor

https://physics-and-radio-electronics.com/electronic-devices-and-circuits/passive-compone
nts/resistors/carboncompositionresistor.html
https://youtu.be/0qpO1Uajy6I?si=_mt4kLk77BX3wOa2
• Variable Resistor
https://www.electricalvolt.com/variable-resistors/
https://youtu.be/D4DjJDKO6IQ?si=twETXWDhC6AtspA5