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Capacitors

Capacitors

Oct 25, 2021

What are Capacitors?

A capacitor is an electrical component that stores energy in the form of electrical charge like an electric battery [2][3]. The difference between a capacitor and a battery is that a capacitor cannot produce new electrons while a battery can [3]. Capacitors also discharge extremely quickly (less than a second) while batteries take minutes to discharge [3].

All capacitors contain at least two metal plates called electrical conductors. In between these plates, there is an insulator known as a dielectric [2][3].

A capacitor's ability to store charge is known as its capacitance [6] and it is measured in Farads [2][3]. One Farad holds a lot of electrical charge, so capacitors tend to have capacitance values that are measured in quantities as small as Picofarads and Microfarads [2][6]. The amount of charge stored by a capacitor can be calculated according to the equation Q = CV, where Q is the total charge, C is the capacitor's capacitance, and V is the voltage being applied to the capacitor [2].

Capacitors are commonly known as caps [2] and were formerly referred to as condensers [4].

 

Applications

Coupling

Capacitors can let AC signal pass from one part of a circuit to another while blocking DC signal [5][6][7]. This process is known as capacitor coupling [5]. Some real-life applications of coupling include communications systems, where they are used to block DC signals in the transmission lines, [6] and loudspeakers, where alternating current is converted into sound while preventing direct current from reaching the speaker [5].

Decoupling

Decoupling is essentially the opposite of coupling. It can be described as filtering out AC signals so that only the DC component of a signal can pass through [6][7]. Decoupling opposes and filters out voltage spikes in a circuit and stabilizes the circuit by providing or absorbing energy when necessary [6].

Energy Storage

Capacitors store electrical energy in the form of electrical charge. A capacitor can be connected to a power source to accumulate energy and then it can release this energy when it is disconnected from the power source [6]. A common application of using a capacitor to store energy is a camera flash. A capacitor is used to store energy in the form of charge and when the shutter button is clicked to take a picture, the capacitor discharges extremely quickly causing the flash [5][6].

Smoothing

Capacitors can smooth current to convert AC into DC [5]. AC can be visualized as a waveform that is not smooth and is varying between zero and peak voltage [7]. A capacitor can charge up as the AC heads towards peak voltage and then discharge once peak voltage is reached before starting to charge up again [5]. This allows a capacitor to supply voltage when necessary [7] in order to prevent output current from dipping by a large amount [5]. This allows the output current to act similarly to direct current [5].

Timing

Capacitors can be used in time-dependent circuits since they charge and discharge at regular intervals [5][7]. Thus, they can determine the time it takes for a circuit to operate [7]. Some real-life applications of capacitors being used for timing include LEDs and loudspeaker systems as well as any flashing light or beeping that occurs at regular intervals [5].

 

Materials and Types

The dielectric of a capacitor can be made from various different materials including [1][9][10]:

  • Aluminum

  • Ceramic

  • Glass

  • Niobium oxide

  • Paper

  • Plastic

  • Silver mica

  • Tantalum

Capacitors can be broken down into two categories: fixed and variable. Fixed capacitors have unchangeable capacitance values, while variable capacitors have capacitance values that can be changed [1].

Capacitors can be further classified by the material that makes up their dielectric [1].

Capacitors can be described as either polar or non-polar. Polar capacitors have a positive and negative terminal marked [9] and the positive terminal must be connected to the power [2] or else the capacitor could be destroyed [9]. Non-polar capacitors are able to be connected either way in a circuit [9].

Figure 2: Circuit symbols for standard and polarized capacitors [2]

 

 

Fixed Capacitors

Ceramic Capacitors

Figure 3: Ceramic capacitors [11]

Electrolytic Capacitors

Figure 4: An aluminum electrolytic capacitor [14]

Figure 5: A tantalum capacitor [15]