Download - Chandra shekhar resistor
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Prepared by:
Chandra Shekhar KNTTF-SIT, Tumkur Centre
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• Can I say resistor as A hump in a smooth road?
How ?
A dam in between a river?HOW?
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Look at this
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Look at this
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RESISTOR CURRENT
ROAD
CIRCUIT PATH
• A resistor is an component that limits the
flow of current in a circuit.
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RESISTOR CONNECTIONS
EQUIVALENT CIRCUITRESISTOR IN SERIES
RESISTOR connections
RESISTOR IN PARALLEL EQUIVALENT CIRCUIT
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The two main characteristics of a resistor are its
resistance, R, in ohms and its power rating, P, in Watts.
The resistance, R, provides the required reduction in
current or the desired drop in voltage.
The wattage rating indicates the amount of power the
resistor can safely dissipate as heat.
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• Resistors are commonly used to perform two functions in a
circuit.
• The first use is to limit the flow of current in a circuit.
I = E / RI = 15 V / 30 ΩI = 0.5 A
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Exceeding the power rating causes damage to a resistor.
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• The second use is to produce a
voltage divider.
TYPES OF RESISTORS
Types of Resistors
– Carbon-composition resistors
– Wire-wound resistors
– Film-type resistors
• Carbon film
• Metal film
Fixed resistors have only one ohmic value, which cannot be changed or
adjusted. One type of fixed resistor is the carbon composition resistor.
TYPES OF RESISTORS
Carbon resistors are very popular for most applications because
they are inexpensive and readily available in standard sizes and
wattages.
½ Watt 1 Watt 2 Watt
TYPES OF RESISTORS
TYPES OF RESISTORSCarbon Film Resistors
Compared to carbon composition resistors, carbon-film
resistors have tighter tolerances, are less sensitive to
temperature changes and aging, and generate less noise.
Metal film resistors are another type of fixed resistor. These resistors
are superior to carbon resistors because their ohmic value does not
change with age and they have improved tolerance.
TYPES OF RESISTORS
Wire-wound resistors are fixed resistors that are made by winding
a piece of resistive wire around a ceramic core. These are used
when a high power rating is required.
TYPES OF RESISTORS
TYPES OF RESISTORS
Variable resistors can change their value over a specific range. A
potentiometer is a variable resistor with three terminals.
RESISTORThe resistor color code are used to determine the resistor’s ohmic value
and tolerance.
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Review:
1. Resistors are used in two main applications: as
voltage dividers and to limit the flow of current in a
circuit.
2. The value of fixed resistors cannot be changed.
3. There are several types of fixed resistors such as
composition carbon, metal film, and wire-wound.
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4. Carbon resistors change their resistance with age or
if overheated.
5. Metal film resistors never change their value, but
are more expensive than carbon resistors.
6. The advantage of wire-wound resistors is their high
power ratings.
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7. Resistors often have bands of color to indicate
their resistance value and tolerance.
8. Resistors are produced in standard values.
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9. Variable resistors can change their value within the
limit of their full value.
10. A potentiometer is a example of variable resistor .
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Special types of resistors
Special types of resistors
LDR
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VDR
Light dependent resistor
LDR
LDR
• It is a Special type of resistor whose resistance depends on the amount of light falling on it.
Definition
Symbol
• The arrows represent light falling on the LDR
LDR
• When light falls on an LDR its resistance falls rapidly.
• In low light or the dark – they act as high resistors.
• In bright light they offer very little resistanceLight level
Resistance of an LDR
Working Principle
• Automatic lighting control• Smoke detection• Burglar alarm systems• Automated Rear View Mirror• Position Sensor• Camera Exposure Control
Applications
Click here to see datasheet of LDR
ThermistorsTemperature-dependent resistors
Thermistor
• It is a Special type of resistor whose resistance depends on the temperature.
Definition
Symbol
Thermistors can be classified into two types ,depending on the classification of K.
1. Positive temperature coefficient (PTC)
If K is positive, the resistance increases with increasing temperature, and the device is called a positive temperature coefficient (PTC) thermistor.
2. Negative temperature coefficient (NTC)
If K is negative, the resistance decreases with increasing temperature, and the device is called a negative temperature coefficient (NTC) thermistor
Types of Themrister
Increase in current through the device will raise its temperature, causing a change in its terminal resistance.
Note :Change in resistance depends on type of thermister which we going to use.
Working principle
Application
current-limiting devices for circuit protection
heater
automotive applications.
(For example, they monitor things like coolant temperature and/or oil temperature inside the engine)
Smoke detectors
Temperature measurement, sensing and control circuits
VDRVoltage-dependent resistor also known as Varistor
Definition
Symbol
It is a Special type of Resister whose resistance depends on the Applied input voltage.
VDR
At low voltage it has a high electrical resistance which decreases as the voltage is raised.
Working principle
The most common type of varistor is the metal-oxide varistor (MOV).
This contains a ceramic mass of zinc oxide grains, in a matrix of other metal oxides (such as small amounts of bismuth, cobalt, manganese) sandwiched between two metal plates (the electrodes).
Application
High voltage varistor
• Overload protection• Telecom line protection• Surge voltage protection at Telecominstallations and AC lines• PTC relays for compressors start• LED current regulation• Heating elements• Inrush current limiting
Any questions??????????