RESISTOR

Prepared by:

Chandra Shekhar KNTTF-SIT, Tumkur Centre

RESISTOR

• 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

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

THERMISTOR

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??????????