Resistor full notes | Colour Code
Resistor :
A resistor is a passive component. It introduce resistance that is opposition to flow of current in a circuit.
Resisters are used in electronic circuit for transistor biasing, voltage division, controlling gain, fixing time constants, matching and loading circuits, heat generation and related applications.
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| Resistor |
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Characteristics of Resistor :
1. Temperature coefficient : Resistance changes with change in temperature. When temperature Coefficient increases then resistance is also increases. It is denoted by Alpha.
2. Voltage coefficient : voltage coefficient of resistance is defined as the percentage change in the value of resistance per unit applied voltage.
3. frequency range : the register may be pure resistance at low frequency but it it may have a capacitive or inductive impedance at high frequencies. The frequency upto which it is resistive, is called frequency range.
4. Resister noise : The noise output of a resistor depends on its thermal noise plus a noise due to applied current.
5. Max. voltage rating : The maximum voltage that can be applied to a resistor without any damage is called max. voltage rating and is given by
Vmax = (Power Rating × Resistance value)½
= (P× R)½
6. Power rating : The maximum amount of heat dissipated by a resistor at max. specified temperature, without damage to resister is called power rating of resistor.
7. Tolerance : This is the accuracy to which the value of resistor can be made of selected.
8. Solderability : When resistors are soldered, due to overheating the resistance changes.
9. Humidity Classification : This refers to change in value of resistance after following a standard high temperature and humidity cycling test. The change is usually expressed in percentage.
10. Voltage proof : This is maximum voltage which can be applied between resistor body and external conductor. Thus it is the breakdown voltage of the insulating coating of resistor.
Manufacturing of Resistors :
1. Preparation of substrate or base
2. Preparation of resistive element
3. End connections or terminal fitting
4. Identification marking.
Types of Resistor :
There are two types of Resistor:-
1. Fixed Resistor
2. Variable Resistor
Fixed value Resistor :
The fixed value resistors are those whose resistance is fixed and cannot be changed.
Types of fixed Resistor :
(a) Carbon composition resistor
(b) Metal film resistor
(c) Carbon film resistor
(d) Wire wound resistor
(e) Alloy resistor.
Variable Resistor :
Variable resistor permits adjustment of resistance value between 0 to maximum.
Types of Variable Resistor :
(a) carbon composition variable resistor
(b) wire wound variable resistor
(c) Cermet type variable resistor
1. Thermistor
- Non linear Resistor can be divided into three categories :
2. Voltage dependent Resistor (VDR)
3. Light dependent Resistor (LDR)
Colour Coding of Resistor :
The value of resistance is coded on the resistor using three or four or five colour bands.
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| Colour coding of resistor |
Resistor colour Code
Failure in Resistor :
The failure rate and mode of a resistor depends upon it's type, the method of manufacture, the operating and environment conditions and resistance value.
Variable resistor has a moving part and depends for its operation on a good contact between the wiper and a resistance track is wound to have highesr failure rate than fixed type. Failures rate depends upon the manufacturing method.
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