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The Basics of Capacitors

The Basics of Capacitors

  • Friday, 17 May 2024
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The Basics of Capacitors

Capacitors are passive electronic components that store energy by holding apart pairs of opposite charges. Since a positive and negative charge naturally want to come together, when they are held a fixed distance apart by an insulator such as air or plastic film their mutual attraction stores potential energy that can be released later when the plates are re-united. Capacitors are one of the fundamental building blocks of electronics.

The value of a capacitor is determined by its capacitance, C, which is the product of its plate area A and its separation distance D. The area of the plates can be varied and the geometry can be altered to alter the capacitance; in fact, a capacitor's shape will affect its performance. The plates can be rolled, folded, crumpled or stacked, and the spacing can be changed by using different dielectric materials. The physical size of a capacitor can also be varied, as can the voltage rating (often referred to as its ripple voltage).

A capacitor's electrolytic fluid can have a wide range of viscosities; for example, the low-temperature oil used in automotive capacitors tends to be thicker than the high-temperature liquids employed in industrial capacitors. The temperature and humidity of the environment in which a capacitor is used may affect its life cycle as well.

Capacitors can be rated in accordance with the safety requirements of various regulatory bodies. In general, devices designed for use in applications where failure could pose a shock hazard are designated with an alphanumeric safety designation such as X1, X2, etc., while those designed for use in AC line applications are typically designated with a number that indicates their level of tolerance to surge voltages.

When connected to a source of current, the capacitor will charge up until the new electrons from the source have saturated the plates and are no longer able to push more electrons across the gap to the other plate. At that point the first plate will be repelled by the negative charge on the second plate, and the other plate will be attracted to the positive charge on the first plate.

Similarly, when a capacitor is discharged, the plates will attract each other until the net electric field between the plates dissipates to zero and they become neutral again. This process can be interrupted by the application of an external circuit that provides a new current to either plate.

Capacitors can also be used to filter electrical signals. For example, they are often used in audio equipment to separate low frequency signals from higher frequencies, and they are commonly found in diode rectifiers that convert AC to DC voltage. They are also very useful in limiting the output of a power supply and are a crucial component of automotive alternators. Capacitors are able to "store" excess energy when a power supply is operating at full capacity, and can release that stored energy when the demand is greatest. This capability helps to smooth AC input voltages and prevent the build-up of excessive ripple.

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