What is capacitance? Electric capacitance is the ability of a conducting body to accumulate charge. The capacitance value of a capacitor is obtained by using the formula: where C is the capacitance, Q is the amount of charge stored on each electrode, and V is the voltage between the two electrodes. In real life circuits the amount of charge on one plate equals the amount of charge on the other plate of a capacitor, but these two charges are of different signs. By examining this formula it can be deduced that a 1 F capacitor holds 1 C of charge when a voltage of 1V is applied across its two terminals. The unit of capacitance The unit of capacitance is a Farad [F]. This unit can be somewhat impractical. From the vantage point of most electrical engineers, one farad is a huge capacitance value. Most electronic circuits use capacitors of only up to a few mF. There are several good reasons for this. One reason is that, when dealing with signals in an electrical circuit, as the frequency of the signal increases, the need for high capacitance capacitors decreases because, at higher frequencies, even a small capacitor can make a big impact on the circuit. Since most modern digital circuitry has a tendency to move towards higher frequencies in order to meet demands for improved processing speed, these circuits mostly use capacitors of only up to a few mF. As a result, the need for large capacitors is virtually non-existent in the signals processing parts of electrical circuits. Another reason is that high capacitance capacitors are physically large. Therefore, the use of such capacitors is avoided, especially in mobile devices. However, there have been recent technology advances in the field of supercapacitors. Thanks to these advances, it is now possible [… read more]

What are electrolytic capacitors? An electrolytic capacitor is a type of capacitor that uses an electrolyte to achieve a larger capacitance than other capacitor types. An electrolyte is a liquid or gel containing a high concentration of ions. Almost all electrolytic capacitors are polarized, which means that the voltage on the positive terminal must always be greater than the voltage on the negative terminal. The benefit of large capacitance in electrolytic capacitors comes with several drawbacks as well. Among these drawbacks are large leakage currents, value tolerances, equivalent series resistance and a limited lifetime. Electrolytic capacitors can be either wet-electrolyte or solid polymer. They are commonly made of tantalum or aluminum, although other materials may be used. Supercapacitors are a special subtype of electrolytic capacitors, also called double-layer electrolytic capacitors, with capacitances of hundreds and thousands of farads.  This article will be based on aluminum electrolytic capacitors. These have a typical capacitance between 1µF to 47mF and an operating voltage of up to a few hundred volts DC. Aluminum electrolytic capacitors are found in many applications such as power supplies, computer motherboards and many domestic appliances. Since they are polarized, they may be used only in DC circuits. Electrolytic capacitor definition An electrolytic capacitor is a polarized capacitor which uses an electrolyte to achieve a larger capacitance than other capacitor types. Reading the capacitance value In the case of through-hole capacitors, the capacitance value as well as the maximum rated voltage is printed on the enclosure. A capacitor that has “4.7μF 25V“ printed on it has a nominal capacitance value of 4.7μF and a maximum voltage rating of 25 volts, which is never to be exceeded. In the case of SMD (surface mounted) electrolytic capacitors, there are two basic marking types. The first one clearly states the value in microfarads [… read more]