Capacitor Specifications

When you are looking for a capacitor for a particular application, it’s important to find a component that has the right specifications for the job. Here are two of the most important specifications to watch for.

Tolerance

Capacitors are rated according to how nearly their values can be expected to match the rated capacitance. The most common tolerance is 10%; some capacitors are rated at 5% or even at 1%. The lower (or tighter) the tolerance number, the more closely you can expect the actual component value to match the rated value. For example, a 10% capacitor rated at 100 pF can range from 90 to 110 pF. But if the tolerance is 1%, the manufacturer guarantees that the capacitance will be between 99 and 101 pF.

Problem 1

A capacitor is rated at 0.10 μF 10%. What is its guaranteed range of capacitance? First, multiply 0.10 by 10 percent to get the plus-or-minus variation. This is 0.10 × 0.10 = 0.010 μF. Then add and subtract this from the rated value to get the maximum and minimum possible capacitances. The result is a range of 0.09 to 0.11 μF.

Temperature Coefficient

Some capacitors increase in value as the temperature increases. These components have a positive temperature coefficient. Some capacitors decrease in value as the temperature rises; these have a negative temperature coefficient. Some capacitors are manufactured so that their values remain constant over a certain temperature range. Within this span of temperatures, such capacitors have zero temperature coefficient.

The temperature coefficient is specified in percent per degree Celsius (%/°C). Sometimes, a capacitor with a negative temperature coefficient can be connected in series or parallel with a capacitor having a positive temperature coefficient, and the two opposite effects cancel out over a range of temperatures. In other instances, a capacitor with a positive or negative temperature coefficient can be used to cancel out the effect of temperature on other components in a circuit, such as inductors