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Resistor
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A resistor is a two-terminal electrical or electronic component that opposes an electric current by producing a voltage drop between its
terminals in accordance with Ohm's law:
The electrical resistance is equal to the voltage drop across the resistor divided by the current through the resistor while the temperature remains the same. Resistors are used as part of electrical networks and electronic circuits.
Most axial resistors use a pattern of colored stripes to indicate resistance. Surface-mount ones are marked numerically. Cases are usually brown, blue, or green, though other colors are occasionally found such as dark red or dark grey.
Four-band axial resistors
Four-band identification is the most commonly used color coding scheme on all resistors. It consists of four colored bands that are painted around the body of the resistor. The scheme is simple: The first two numbers are the first two significant digits of the resistance value, the third is a multiplier, and the fourth is the tolerance of the value. Each color corresponds to a certain number, shown in the chart below. The tolerance for a 4-band resistor will be 1%, 5%, or 10%.
| Color | 1st band | 2nd band | 3rd band (multiplier) | 4th band (tolerance) | Temp. Coefficient |
|---|---|---|---|---|---|
| Black | 0 | 0 | �100 | ||
| Brown | 1 | 1 | �101 | �1% (F) | 100 ppm |
| Red | 2 | 2 | �102 | �2% (G) | 50 ppm |
| Orange | 3 | 3 | �103 | 15 ppm | |
| Yellow | 4 | 4 | �104 | 25 ppm | |
| Green | 5 | 5 | �105 | �0.5% (D) | |
| Blue | 6 | 6 | �106 | �0.25% (C) | |
| Violet | 7 | 7 | �107 | �0.1% (B) | |
| Gray | 8 | 8 | �108 | �0.05% (A) | |
| White | 9 | 9 | �109 | ||
| Gold | �10-1 | �5% (J) | |||
| Silver | �10-2 | �10% (K) | |||
| None | �20% (M) |
Preferred values
Resistors are manufactured in values from a few milliohms to about a gigaohm; only a limited range of values from the IEC 60063 preferred number series are commonly available. These series are called E6, E12, E24, E96 and E192. The number tells how many standardized values exist in each decade (e.g. between 10 and 100, or between 100 and 1000). So resistors conforming to the E12 series, can have 12 distinct values between 10 and 100, whereas those confirming to the E24 series would have 24 distinct values. In practice, the discrete component sold as a "resistor" is not a perfect resistance, as defined above. Resistors are often marked with their tolerance (maximum expected variation from the marked resistance). These E numbers correspond to the formula R= 10^(N/E), So for an 1.21 ohm E96 series resistor, N=8 and 10^(8/96)=1.21 ohm. Each multiple of 96 added to the remainder gives the next decade. So a 12.1 ohm resistor would have a N= 8+96 = 104. N can also be found by using the formula E*LOG10(R) = N.
5-band axial resistors
5-band identification is used for higher precision (lower tolerance) resistors (1%, 0.5%, 0.25%, 0.1%), to notate the extra digit. The first three bands represent the significant digits, the fourth is the multiplier, and the fifth is the tolerance. 5-band standard tolerance resistors are sometimes encountered, generally on older or specialized resistors. They can be identified by noting a standard tolerance color in the 4th band. The 5th band in this case is the temperature coefficient.
SMT resistors
Surface mounted resistors are printed with numerical values in a code related to that used on axial resistors. Standard-tolerance Surface Mount Technology (SMT) resistors are marked with a three-digit code, in which the first two digits are the first two significant digits of the value and the third digit is the power of ten (the number of zeroes). For example:
"334" = 33 � 10,000 ohms = 330 kiloohms
"222" = 22 � 100 ohms = 2.2 kiloohms
"473" = 47 � 1,000 ohms = 47 kiloohms
"105" = 10 � 100,000 ohms = 1 megaohm
Resistances less than 100 ohms are written: 100, 220, 470. The final zero represents ten to the power zero, which is 1. For example:
"100" = 10 � 1 ohm = 10 ohms
"220" = 22 � 1 ohm = 22 ohms
Sometimes these values are marked as "10" or "22" to prevent a mistake. Resistances less than 10 ohms have 'R' to indicate the position of the decimal point (radix point). For example:
"4R7" = 4.7 ohms
"0R22" = 0.22 ohms
"0R01" = 0.01 ohms
Precision resistors are marked with a four-digit code, in which the first three digits are the significant figures and the fourth is the power of ten. For example:
"1001" = 100 � 10 ohms = 1 kiloohm
"4992" = 499 � 100 ohms = 49.9 kiloohm
"1000" = 100 � 1 ohm = 100 ohms
"000" and "0000" sometimes appear as values on surface-mount zero-ohm links, since these have (approximately) zero resistance.
Industrial type designation
Format: [two letters]
| Type No. | Power rating (watts) |
MIL-R-11 Style |
MIL-R-39008 Style |
|---|---|---|---|
| BB | 1/8 | RC05 | RCR05 |
| CB | � | RC07 | RCR07 |
| EB | � | RC20 | RCR20 |
| GB | 1 | RC32 | RCR32 |
| HB | 2 | RC42 | RCR42 |
| GM | 3 | - | - |
| HM | 4 | - | - |
| Industrial type designation | Tolerance | MIL Designation |
|---|---|---|
| 5 | �5% | J |
| 2 | �20% | - |
| 1 | �10% | K |
| - | �2% | G |
| - | �1% | F |
| - | �0.5% | D |
| - | �0.25% | C |
| - | �0.1% | B |