Resistor Image

In the electronics there are so many components are present. These components are of two types.

ACTIVE COMPONENTS

These components can be used for amplification, rectification or to change energy from one form to another. The semiconductors, electron tubes and display devices are active components.

PASSIVE COMPONENTS

These components cannot be used for amplification or rectification etc. Resistors, capacitors and inductors are passive components


Resistors -

The opposition to flow of electronics is called resistance. Although resistance provides opposition to flow of electrons, it is used in circuit to reduce the current to specific value or to provide desired voltage drop.

 

Specification of Resistors -

1.  Resistance R in ohms.

2.  Power rating in watts (w).

3. Resistors with higher Revalues have less current; therefore they have smaller wattage ratings.

4. The actual physical size of the resistor indicates the power rating. As physical size increases the power rating increases


Types of Resistors 



Types of Resistor Image

A. Fixed Resistor

This resistors provide a fixed value of resistance.

 

1. Wire wound resistors

a) These resistors are used where accurate stable resistance values are necessary .

b) They are generally used for high current applications with low resistance.

Wire Wound Resistor Image


2. Carbon composition resistors

a) The resistance values are from 1Ω to 20MΩ.

b) The power rating generally 1/10,1/8,1/4,1/2,1 or 2w.

c) Color code is used to indicate the resistance.


3.Film-type fixed resistors

a) These resistors provide more accurate R values.

b) Film-type resistors are used in measuring instruments where very small tolerance required.

Note - The amount by which actual resistance can be different from the colour coded values is called tolerance.

Film type fixed resistor Image


Nonlinear Resistors

These resistors don’t follow ohms law.

1. Thermistor

a)   Their resistance depends upon temperature.

b) In negative temperature coefficient type thermistor,the resistance with increase in temperature while in positive temperature coefficient type, the resistance increases with increase in temperature.

These are used in temperature sensor and control circuits.

Thermistor Image

2. Veristor

a)  In this type resistor depends on applied voltage.

b)  These are also called as voltage dependent resistor VDR.

c) These are used to protect circuits and components from sudden changes in voltage.

B. Variable Resistor

a) A variable resistor can be set at any value between zero and it’s fill maximum resistance.

b) These resistors may be of wire-wound type or carbon composition type.


Types Of Variable Resistor



1. Rheostat

a) It has two terminals.

b) It is used to change value of current.

c) Rheostats are generally wire-wound height voltage resistor.

Rheostat Image

2. Potentiometer    

a) It has three terminals. It is generally called as pot.

b) The fixed maximum R across the two ends is connected across voltage source.

c) A potentiometer can be used to change voltage between centre terminal and the ends.

d) A potentiometer can be used as a low voltage rheostat.

e) Pot can be used as a rheostat for continuous tone control in a receiver.


Potentiometer Image

 

3. Preset

a) These are the potentiometers used for adjusting resistance value to the current required value.

b) Preset potentiometers are called trimmers in which carbon composition and wire wound elements are used.

c) The resistance ranges is from 100Ω to 1MΩ.

d) These are smaller in size and cheaper than potentiometers.

e) Presets are available in two types single turn and multi turn presets.

 

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