This section provides overview, applications, and principles of metal film resistors. Also, please take a look at the list of 22 metal film resistor manufacturers and their company rankings.
Two types of fixed resistors are widely used in circuits: carbon resistors and metal film resistor. Carbon and metal film refer to the material of the resistive element.
Metal film resistor is similar in structure to carbon resistors and use a metal such as nickel-chromium for the resistive element. Compared to carbon resistors, metal film resistor can be made with higher resistance accuracy.
Metal film resistors are fixed resistors that use a metal film for the resistive element. They are characterized by low resistance tolerance, low temperature coefficient of resistance, and small change over time, making them highly accurate and stable resistors. They also have the advantage of low current noise.
Taking advantage of these characteristics, metal film resistors are mainly used in the field of industrial equipment such as communication and measuring equipment, as well as in circuits that handle minute signals such as computers and peripheral equipment and audio/visual equipment.
There are two types of metal film resistors: thick film type and thin film type. The thin-film type is a higher precision (±0.05%) version of the thick-film type. The thick-film type is made by heating and firing a metallic paste, while the thin-film type is coated by vapor-depositing a metal. While the temperature characteristic of general metals is positive, the temperature coefficient of Metal film resistors is reduced by changing the ratio of alloys. Therefore, the ratio determines whether the resistor will have a positive or negative characteristic.
Resistors are available in two types: those with resistance printed on them and those with color-coded resistor values. In the case of color code indication, the "upper two digits" or "upper three digits" of the resistance value are indicated in 10 colors, with black as 0 and gray as 9. By reading these colors, the resistance value of the resistive element can be determined. Similarly, multipliers, tolerances, temperature coefficients, etc. can also be determined by the color code system.
Metal film resistors have many advantages over carbon resistors, but they are also more expensive. Therefore, the advantages of metal film resistors (thick film type in this case) over carbon resistors are introduced below.
Tolerance of resistance value is generally ±5% for carbon resistors, while metal film resistors can be selected with less error of ±2%, ±1%, and ±0.5%.
As for temperature counting of resistance value, carbon resistors show a negative temperature series number of -200 to -800ppm/℃, while metal film resistors show relatively small temperature variation, classified into ±200ppm/℃, ±100ppm/℃, and ±50ppm/℃, which can be selected from among them.
As shown in the circuit example, carbon resistors are used when not much resistance accuracy is required, such as current limiting resistors for light emitting devices, etc., bias resistors for amplifiers, and pull-up resistors found in digital circuit interfaces.
On the other hand, metal film resistors are used when accurate and stable resistance values are required, such as in DC amplification circuits where temperature drift is a problem, filter circuits where strict cutoff frequency is required, and amplifier circuits where amplification factor is strictly set.
Lead wire type or MELF type resistors indicate resistance value, error, and temperature coefficient by color code.
The numerical value indicated by the color code is specified in JIS C 5062.
The number of bands (color bands) on a resistor can be 3, 4, 5, or 6. 4-band (resistance and error are indicated by 4 bands) and 5-band (resistance and error are indicated by 5 bands) are commonly used.
The two or three lines from the left represent the resistance value, and the one line after that represents the multiplier.
Carbon resistors usually have a four-band display, with the second line from the left indicating the resistance (two significant digits) and the third line indicating the digit in the multiplier, and the fourth line indicating the error, which is generally gold (5%).
Metal film resistors, on the other hand, have three significant digits for high accuracy. Therefore, the third digit from the left is the resistance value, and the fourth digit is the multiplier. The fifth digit indicates the error, which can be green (0.5%), brown (1%), red (2%), etc.
In addition, the sixth line may indicate the temperature coefficient, but the color code may spread over the entire resistor, making it difficult to read.
Usually, bands indicating resistance and multiplier are grouped together and printed close to each other. Therefore, the space between the four bands on the left and the error band is somewhat wider than the space between the other bands, which can be used as a clue to read the resistance value.
In other cases, the error bands are wider than the other bands. Using this as a clue, the resistance value can be read by identifying the band that shows the error.
*Including some distributors, etc.
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