Resistors are commonly used and well-known passive elements in electronic design. With their function of resisting the current flow in a circuit, plenty of applications can be realized through resistors, such as voltage dividers, current dividers, loads, and so on. Hence, it is easy to find resistors everywhere in any electronic circuit. In this article, the important specifications of a resistor will be introduced for readers to select resistors more conveniently. In general, resistors can be classified into fixed and variable resistors.
The most essential specifications of a resistor are resistance, tolerance, power rating, and temperature coefficient.
Resistance refers to the degree of a resistor resisting the current flow that goes through it. With a wide variety of ranges, the resistance of a resistor can be as high as megaohms or as low as less than 1 ohm. The EIA (Electronic Industries Association) has specified standard resistor values and classified them into E3, E6, E12, E24, E48, E96, and E192 series, which are so-called E-series. The rule of this classification will be explained in the next section “tolerance”.
The tolerance of a resistor defines the variation range of the resistor’s resistance. It is the deviation that the resistor will vary from its nominal resistance, which is measured at room temperature (25oC) with no load applied. It is one of the factors that affect the accuracy and precision of a resistor. The E-series addressed below are classified by tolerance, and the E-series numbers represent the resistor numbers in each decade, i.e., E6 has 6 resistors in each decade.
|E-series||Tolerance (SIG FIGS)|
|E24||5% ( also available in 2% )|
|E192||0.5%, 0.25% and higher tolerances|
A resistor working under its power rating can ensure a safe and stable outcome without generating extra heat. The power rating usually ranges from less than 1W (such as 1/16W) to hundreds of watts, and it has a positive correlation with the size of a resistor. The larger the size of a resistor is, the higher its power rating is.
The resistance of a resistor slightly varies when the temperature changes. Normally, the resistance at room temperature 25°C is the reference base, and the temperature coefficient unit is ppm.
Resistance, tolerance, power rating, and temperature coefficient are the most important specifications that you should consider when selecting a resistor. Other than these, there are still other resistor specifications such as voltage coefficient, high frequency performance, stability, size, and so on. Discussing with a trustworthy resistor supplier, such as Walsin, will be the fastest way to get the most suitable resistors for your applications.