What is resistor and resistor calculations.
- What is resistor
- Ohm's law
- Resistors in parallel
- Resistors in series
- Dimensions and material affects
- Resistor image
- Resistor symbols
- Resistor color code
- Resistor types
Resistor is an electrical component that reduces the electric current.
The resistor's ability to reduce the current is called resistance and is measured in units of ohms (symbol: Ω).
If we make an analogy to water flow through pipes, the resistor is a thin pipe that reduces the water flow.
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
The total equivalent resistance of resistors in parallel RTotal is given by:
So when you add resistors in parallel, the total resistance is decreased.
The total equivalent resistance of resistors in series Rtotal is the sum of the resistance values:
Rtotal = R1+ R2+ R3+...
So when you add resistors in series, the total resistance is increased.
The resistance R in ohms (Ω) of a resistor is equal to the resistivity ρ in ohm-meters (Ω∙m) times the resistor's length l in meters (m) divided by the resistor's cross sectional area A in square meters (m2):
|Resistor (IEEE)||Resistor reduces the current flow.|
|Potentiometer (IEEE)||Adjustable resistor - has 3 terminals.|
|Variable Resistor / Rheostat (IEEE)||Adjustable resistor - has 2 terminals.|
|Variable Resistor / Rheostat (IEC)|
|Trimmer Resistor||Presest resistor|
|Thermistor||Thermal resistor - change resistance when temperature changes|
|Photoresistor / Light dependent resistor (LDR)||Changes resistance according to light|
The resistance of the resistor and its tolerance are marked on the resistor with color code bands that denotes the resistance value.
There are 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.
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
|Variable resistor||Variable resistor has an adjustable resistance (2 terminals)|
|Potentiometer||Potentiometer has an adjustable resistance (3 terminals)|
|Photo-resistor||Reduces resistance when exposed to light|
|Power resistor||Power resistor is used for high power circuits and has large dimensions.|
|SMT/SMD resistors have small dimensions. The resistors are surface mounted on the printed circuit board (PCB), this method is fast and requires small board area.|
|Resistor network||Resistor network is a chip that contains several resistors with similar or different values.|
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.
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.
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