Resistor

What is resistor?

                        Resistor is a passive electrical component, that limit or regulate the flow of electrical current in an electronic circuit.

1. Resistor is a passive electrical component.

2. Main function of resistor in any circuit is to restrict the flow of electric current in an electronic circuit.

3.Resistors are used in electronic circuits,reduce current  flow, and adjust signal levels, to divide voltages   and etc.

Resistor Symbols

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Type of Resistors:-

Type of Resistor?

Resistor classified into:- 

                1. Linear resistor

                2. Non-linear resistor

1. Linear resistor

               Resistance does not vary with the flow of current through it

                         Directly proportional to the applied voltage

               In other words Resistance remains constant

Linear resistor are further classified into:-

                    1. Fixed resistor

                    2. Variable resistor

1. Fixed resistor:-

    Fixed resistor Have a constant resistance value

                      Can’t change the value of resistance

Fixed resistor is further classified into:-

                          1.     Carbon Composition Resistors

                          2.     Wire Wound Resistors

                          3.     Thick Film Resistors

                          4.     Thin Film Resistors

         

1. Carbon composition resistor:-

Made from the carbon or graphite with an insulating material,

Insulating material as a binder desired the original resistance of the resistor. 

                     Commonly available in Resistance values of 1 Ω to 25 MΩ.

                     The power rating is generally 1⁄10, 1⁄8, 1⁄4, 1⁄2, 1, up to 5 Watts.

2. Wire wound resistor:-

Wire wound resistor is made by the insulating core.

The insulating core is porcelain, Bakelite, plain pressed paper etc.

The resistive wire is wrapped around an insulating core

The resistance wire include tungsten and manganin, Nichrome etc.

The resistance of the resistor depends on the resistivity of the wire,

The resistance can be less than 1 Ω up to several thousand Ωohms

Wattage ratings from 1 Watt up to 100 Watt or more.

Uses of Wire Wound Resistors

                     Used in high power rating devices

                     Used in Testing and measuring devices

                     Used in current and voltage balancing

                     Used in current sensing

Advantages:-

                      Make lower noise

                      Reliable and flexible

                      Low cost

                      Wide resistance range

                      High accuracy/ stability

Disadvantage:-

 Used only low frequency equipment,

                      Not suitable for high frequency equipment.

3. Thick film:-

Thick film resistors are manufactured using screen and stencil printing processes.

The alumina substrate is metalized then a resistive paste is deposited on top of the terminals.

It is later trimmed, coated, metalized on the edges, and plated.

Most SMD (surface mount device) resistors today are of this type.

Thick film resistor classified into:-

                    1. Metal Oxide film Resistors
                    2. Cermet Film Resistors
                    3. Fusible Resistors

Metal oxide resistor:-

                   Metal-oxide film resistors are made of metal oxides

                   Metal oxide resistor have a higher operating temperature

                   Metal oxide resistor is greater stability/reliability

Cermet film resistor:-

Cermet oxide resistors, contains on ceramic insulation materials.

A carbon or metal alloy film or layer wrapped around the resistor and then fix it in a ceramic metal

Cermet film resistor made in the square or rectangular shape

Fusible film resistor:-

                        When the power rating is exceeded. It then serves the dual functions of a fuse and a resistor to limit.

4.Thin film:-

Thin film resistors are made by sputtering (a method of vacuum deposition) the resistive material onto an insulating substrate, allowing for a much more uniform and controlled resistive element. Then undergo similar finishing steps to trim, coat, and metalize the edges.

Thin film resistors are usually specified with tolerances of 0.1, 0.2, 0.5, or 1%,

They also have much lower noise levels,

Thin film resistors are more expensive than thick film resistors.

Thin film resistor classified into:-

                   1. Carbon Film Resistors
                   2. Metal Film Resistors

Carbon film resistor:-

                Carbon film is deposited on an insulating substrate

                Carbon film resistor Power rating is 0.125 W to 5 W

                Carbon film resistor Resistances range from 1Ω to 10 megaΩ

Metal film resistor:-

               Metal film resistor construction like Carbon film resistors,

               Metal film resistor is usually coated with nickel chromium

               Metal film resistor is very tiny,

               Metal film resistor Cheap and reliable.

Variable resistor:-

      The electric resistance(R) value can be adjusted/changed, during the   operation of equipment is required.in other words said that (increase or decrease the flow of the electric current in a circuit).

Type of variable resistor:-

1.     Potentiometers

2.     Rheostats

3.     Trimmer

1. Potentiometers:-

Potentiometer is a type of variable resistor

Potentiometers resistor have a three terminals

Potentiometers also called a pot

Potentiometer is used to vary the voltage in a circuit

                                 Potentiometer have a continuously adjustable tapping point

 Tapping point controlled by rotation of a shaft or knob

Use of potentiometer:-

                  A volume control for an audio device, frequency attenuation, and more

2. Rheostats:-

                           Rheostats is a type of variable resistor

                           Rheostats resistor have a two terminals

                           Rheostats is used to vary the current in a circuit

Types of rheostats

                          Rotary type

                          Linear type

Application of Rheostats:-

                          Used in volume controller

                          Used in speed controller and more

2. Non-linear resistors:-

            The current flowing through it does not change but changes in applied voltage.  

Type of non-linear resistor:-

                         1. LDR (light dependent resistor)

                         2. VDR (voltage dependent resistor)

                         3. Thermistors

LDR (light dependent register):

LDR is light sensitive resistor and also called photo resistor

LDR is whose resistance decreases as the intensity of light they are exposed to increases.

Types of LDR:-

1                         1. Intrinsic

2                         2. Extrinsic. 
VDR (voltage dependent resistor)

                   Used to protect circuits.

Thermistors:-

Resistance value changes significantly with a change in temperature is called thermistors.

Type of thermistors:-

                 1. NTC

                 2. PTC

NTC (negative temperature coefficient)

Thermistor indicating that its resistance decreases with an increase in operating temperature.

Used in Temperature sensing and control, inrush current limiting, flow measurement

PTC (positive temperature coefficient)

Thermistor indicating that its resistance increases with an increase in operating temperature.

Used in over-current protection, self-regulating heater, time-delays, liquid level sensing.

click here full lesson for SMD(surface mount device)resistor