Capacitance in AC Circuits

22 Jan, 2020 | Quest Components
Capacitance in AC Circuits

Capacitance in AC Circuits

Circuits almost always involve capacitors. These two-terminal electrical components are critical in circuits because they store energy, suppress voltage spikes, and filter complex signals. When a current flows through a capacitor, electrical charges are stored by its plates. The maximum amount of electrical charges that can be stored by a capacitor is its capacitance.

How Capacitors Work in DC Circuits

Capacitors in DC circuits can play a few different roles. These include:

Power Conditioning

Capacitors are frequently used as filters in DC systems. They can be used to convert AC to DC power supply through rectification. DC polar capacitors are used to convert AC power into fluctuating DC power to filter out fluctuation and ripples.


When two electronic circuits must be decoupled, a decoupling capacitor can be used. The decoupling capacitor grounds the noise generated by one of the circuits, which has no impact on the performance of the other circuit.


Capacitors can also play a role in coupling. Because capacitors block DC while allowing AC to flow through, they can be used to separate these signals. Coupling capacitors can also be used in filters to separate AC from DC signals, then convert DC into AC by removing the ripples and using rectification.

How Capacitors Work in AC Circuits

Capacitors play many roles in AC systems as well. Some of these functions include:

Transformerless Power Supply

In a transformerless power supply circuit, a capacitor is connected in series with the load to reduce voltage with a reduced waste of power.

Split Phase Induction Motors

Capacitors play an important role in this type of motor. They take a single-phase supply and split it into a two-phase supply, which in turn produces a revolving magnetic field in a rotor.

Power Factor Correction and Improvement

A capacitor can be used in power factor improvement. Capacitor banks are used in three-phase power systems to supply reactive power to the load, resulting in improved power factor in the system. This reduces losses and boosts overall efficiency.

Capacitive Reactance

We know that capacitors are comprised of two conductors separated by a dielectric, or insulator. The opposition to the charge of voltage across an element is called capacitive reactance. The capacitive reactance is inversely proportional to the signal frequency and the capacitance.

When DC voltage is applied across a capacitor, it causes positive charges to accumulate on one side and negative charges to accumulate on the other. The source of the opposition to the current is the electric field due to the accumulated charge. The current is reduced to zero when the potential associated with the charge balances the applied voltage.

When used in applications with an AC supply, capacitors can only accumulate a limited amount of charge before polarity is changed and the charge is returned to the source. In such circumstances, less charge accumulates and opposition to the current is less with higher frequencies.

Types of Capacitors That Can Be Used in Circuits

Most capacitors labeled as AC can also be used in DC circuit as wells, but DC capacitors cannot be used in AC circuits. Non-polar capacitors, for example, can be connected to a power supply in any direction; their overall capacitance has no impact on the reversal of polarity, so they can be used interchangeably in both AC and DC systems. A polar capacitor, however, is only used in DC circuits because it is sensitive about its polarity and after each half cycle of AC supply would reverse its polarity.

Learn More About Capacitors and Capacitance

If you have questions about capacitors, our expert electricians are available to help. Call (623) 333-5858 today to inquire about a product or place an order or search and order capacitors here. We look forward to working with you.

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