In-depth explanation of common components series - capacitor

1. Capacity

This is the most intuitive parameter of the capacitor, there is nothing to say. However, common capacitors are made of many different materials. Due to the different dielectric constants of different materials, the capacity of different capacitors will vary greatly. For example, the capacitance of aluminum electrolytic capacitors can be as high as several thousand microfarads or even higher, while the ceramic capacitors of C0G can only achieve the level below the nanometer, and the same polypropylene film capacitors can only achieve 0.1uF or so. The limits are closely related to the material of the capacitor.

Common capacitor materials are: aluminum electrolytic capacitors, tantalum electrolytic capacitors, ceramic capacitors (also due to a variety of materials and processes, not expanded here), polyester film capacitors, polypropylene film capacitors, polystyrene film capacitors, poly PTFE film capacitors, de-capacitors, etc.

2. Precision

The accuracy of a capacitor is defined similarly to a resistor and is also used to indicate the difference between the actual value of the capacitor and the nominal value. In general, the accuracy of a capacitor is much lower than that of a resistor. Common capacitor accuracy is generally 20%, 10%, etc., and the polystyrene capacitor (CB), which is often used as a standard capacitor, is only 0.5%, which is basically the highest precision level capacitor we can see.

3. Temperature coefficient

As with precision, the temperature coefficient of the capacitor is also very poor relative to the resistance. Even many capacitors do not have the temperature coefficient index, and the representation method is also downgraded from ppm to %.

4. Loss angle

It is also generally expressed by the loss tangent value, which is a parameter used to represent the capacitance loss. For convenience, some manufacturers include this parameter including the ESR, ESL, dielectric absorption and other parameters of the capacitor; and because ESR is the largest proportion of these parameters, in some cases, this parameter is also corresponding to ESR. . This parameter is also related to the voltage applied across the capacitor. The following figure shows the data on a capacitor datasheet.

These parameters related to the loss angle are determined by the capacitance material, so the capacitance loss angles of different materials vary greatly. As shown in the figure above, the loss tangent of the aluminum electrolytic capacitor can be as high as 0.3, and the loss tangent of a certain polypropylene film capacitor of Panasonic is only 0.1 to 0.2%, and the loss angle of the polystyrene capacitor can reach 0.03%.

5. Leakage current

The capacitor medium cannot be absolutely non-conductive. When the capacitor is applied with a DC voltage, the capacitor will have leakage current. If the leakage current is too large, the capacitor will be damaged by heat. Among all capacitor materials, electrolytic capacitors, especially aluminum electrolytic capacitors, have large leakage currents, so leakage current is used to indicate their insulation performance (proportional to capacity); leakage currents of other capacitors are extremely small, so insulation resistance parameters are used. Indicates its insulation properties.

6. Dielectric absorption

Dielectric absorption is an internal charge distribution with hysteresis properties that restores a portion of the charge to a capacitor that is rapidly discharged and then opened. Since the amount of recovered charge is a function of the original charge, it is actually a charge memory effect. If such a capacitor is used as a holding capacitor in a sample-and-hold amplifier or as an integral capacitor in an integrating circuit, it is bound to cause an error in the measurement result, so that attention must be paid to the selection of the capacitance in such a circuit.

7. Working temperature

Capacitors usually have a nominal operating temperature range. This parameter can be found directly in the datasheet. There are two points to note for electrolytic capacitors. First, the dielectric constant of the dielectric changes with temperature, and the low temperature affects the capacitance. Second, the high temperature reduces the life of the electrolytic capacitor.

8. Rated voltage

The rated voltage of the capacitor is the maximum value of the highest DC voltage or AC voltage that the capacitor can operate continuously and reliably within the specified temperature range. The rated voltage is related to the insulating medium used in the capacitor and the ambient temperature of the capacitor, which is especially close to the temperature.