Component Overview: Resistor
What is a resistor?
An electronic component that resists the flow of current is called a resistor. Almost all components offer resistance. A copper wire has close to zero resistance while the resistance of the air is close to infinity. Resistors are a common component of all electronic and electrical circuits. The most common resistor available is the axial lead resistor as shown in Fig 1. |
| Fig 1. 220 ohm resistor with 5% tolerance |
How to know a resistor value?
Most electronic components use color coding to mark the value of the component. The resistor follow the same technique. Fig 1. shows a regular resistor. Usually it has 4 bands of various colors which needs to be decoded to get the resistor values. Though it is not a very efficient way, it works very well for electronic components has they are very small and printing the actual value on the component may be very small and unreadable causing confusion.
To decode the value of resistor, first get the value of each bands on the resistor using the reference table below. For the resistor in Fig 1. the bonds from left to right are red, red, black and gold. Looking up the values we get 2, 2, 0, 5 which would translate in 22 x 100 - 5%, which is 220Ω with 5% tolerance.
What is tolerance? It means that the actual value of the resistor will be anywhere between 5% of the decoded value. For the above resistor, it can be anywhere between 209 and 231.
For a 5 band resistor, the 4th band is the multiplier and the 5th band is the tolerance value
What is tolerance? It means that the actual value of the resistor will be anywhere between 5% of the decoded value. For the above resistor, it can be anywhere between 209 and 231.
For a 5 band resistor, the 4th band is the multiplier and the 5th band is the tolerance value
More precise the resistor value you need for your circuit, the less the tolerance value you should go for. Consequently the expensive the resistor will be.
Seeing the color on a small resistor can be difficult most of the times. Hence it is better to measure the resistance value using the multimeter before you put it in your circuit
| Ring color | Significant figures | Multiplier | Tolerance | Temperature coefficient | |||||
|---|---|---|---|---|---|---|---|---|---|
| Name | Code | RAL | Percent | Letter | ppm/K | Letter | |||
| None | – | – | – | – | ±20% | M | – | ||
| Pink | PK | 3015 | – | ×10−3[5] | ×0.001 | – | – | ||
| Silver | SR | – | – | ×10−2 | ×0.01 | ±10% | K | – | |
| Gold | GD | – | – | ×10−1 | ×0.1 | ±5% | J | – | |
| Black | BK | 9005 | 0 | ×100 | ×1 | – | 250 | U | |
| Brown | BN | 8003 | 1 | ×101 | ×10 | ±1% | F | 100 | S |
| Red | RD | 3000 | 2 | ×102 | ×100 | ±2% | G | 50 | R |
| Orange | OG | 2003 | 3 | ×103 | ×1000 | – | 15 | P | |
| Yellow | YE | 1021 | 4 | ×104 | ×10000 | ±5% | – | 25 | Q |
| Green | GN | 6018 | 5 | ×105 | ×100000 | ±0.5% | D | 20 | Z |
| Blue | BU | 5015 | 6 | ×106 | ×1000000 | ±0.25% | C | 10 | Z |
| Violet | VT | 4005 | 7 | ×107 | ×10000000 | ±0.1% | B | 5 | M |
| Gray | GY | 7000 | 8 | ×108 | ×100000000 | ±0.05% ±10% | A | 1 | K |
| White | WH | 1013 | 9 | ×109 | ×1000000000 | – | – | ||
Table 1. The standard color code per IEC 60062:2016
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