RESISTOR

Resistors

What is a Resistor?

           A resistor is an electrical component that limits or regulates the flow of electrical current in an electronic circuit.

          Resistors can also be used to provide a specific voltage for an active device such as a transistor.

           The resistor's ability to reduce the flow of current is called resistance and is measured in ohms (symbol: Ω).

           

Resistance:

   Ohm's law:

                                                         R = V  / I

The resistor's current I in amps (A) is equal to the resistor's voltage V in volts (V)

divided by the resistance R in ohms (Ω):

                                                     

The resistor's power consumption P in watts (W) is equal to the resistor's current I in amps (A)

times the resistor's voltage V in volts (V):

                                                      P = I × V

The resistor's power consumption P in watts (W) is equal to the square value of the resistor's current I in amps (A)
times the resistor's resistance R in ohms (Ω):

                                                     P = I ² × R

The resistor's power consumption P in watts (W) is equal to the square value of the resistor's voltage V in volts (V)
divided by the resistor's resistance R in ohms (Ω):

                                                     P = V ² / R

Resistors in parallel

The total equivalent resistance of resistors in parallel R_Total is given by:

So when you add resistors in parallel, the total resistance is decreased.

Resistors in series

The total equivalent resistance of resistors in series R_total is the sum of the resistance values:

R_total = R₁+ R₂+ R₃+...

So when you add resistors in series, the total resistance is increased.

Resistor Symbols 

 

 

 Resistor Color Codes

             There are mainly four color bands provided on the body of resistors and each color indicates unique digit. Such as Black ⇒ 0, Brown ⇒ 1, Red ⇒ 2, Orange ⇒ 3, Yellow ⇒ 4, Green ⇒ 5, Blue ⇒ 6, Violet ⇒ 7 Gray ⇒ 8, White ⇒ 9. The first and second color bands indicate a two digits number. The 3rd color band indicates the power of ten as multiplier. The fourth band indicates the tolerance.

3 types of color codes:

• 4 bands: digit, digit , multiplier, tolerance.
• 5 bands: digit, digit, digit , multiplier, tolerance.
• 6 bands: digit, digit, digit , multiplier, tolerance, temperature coefficient.

 

Calculation:

Resistance calculation of 4 bands resistor

R = (10×digit₁ + digit₂) × multiplier

Resistance calculation of 5 or 6 bands resistor

R = (100×digit₁ + 10×digit₂+digit₃) × multiplier

Types of Resistors

         There are different types of resistor depending upon their construction, power dissipation capacities and tolerance of the value. Such as 

 

 

 

 

 

 

1.  Carbon Composition Resistor
2. Metal Film Resistor
3. Carbon Film Resistor
4. Non Linear Resistor
5. Varistor
6. Thermistor

Pull-up and Pull-Down Resistors 

Pull-up resistor

          In digital circuits, pull-up resistor is a regular resistor that is connected to the high voltage supply (e.g +5V or +12V) and sets the input or output level of a device to '1'.
The pull-up resistor set the level to '1' when the input / output is disconnected. When the input / output is connected, the level is determined by the device and overrides the pull-up resistor.

Pull-down resistor

         In digital circuits, pull-down resistor is a regular resistor that is connected to the ground (0V) and sets the input or output level of a device to ' 0 '.
The pull-down resistor set the level to ' 0 ' when the input / output is disconnected. When the input / output is connected, the level is determined by the device and overrides the pull-down resistor.

Applications of Resistors

       Many electrical devices are based on electrical resistance and Ohm's law, even if they do not have little components in them that look like the usual resistor. The following are some examples.

• Light-bulb
• Polygraph
• Fuse
• Voltmeter, Etc.