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| Resistor Image |
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
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
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| 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.
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| 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.
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| 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.
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| 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.
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| 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.
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| 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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