A Guide to the Applications of Capacitors

Capacitors are one of the fundamental passive electrical components we use in electronic circuits, and are found in almost every electronic device, but what are some of the main applications of these crucial components?

What is a capacitor?

Capacitors are two-terminal passive electrical components created from two metal plates with an insulating dielectric in between. When the current reaches these metal plates, the charges are ‘stuck’ as they are attracted to the opposite charges, but the dielectric prevents them from crossing to the other plate.

When another path in the circuit is created that allows the charges to reach each other, they will discharge from the capacitor.

What are the common applications of capacitors?

Energy storage

Because of the way that they store energy, one of the main applications of capacitors is to use them as a form of temporary battery. In electronic devices and uninterruptible power supplies, capacitors can be used to maintain the power supply when there is a power outage or the batteries are being changed, meaning information is not lost during the process. They are also used in car audio systems by storing energy and then releasing it when the amplifier is activated.

Power conditioning

Another application of capacitors is for power conditioning. The capacitors help power conditioners to provide consistent energy levels by smoothing current fluctuations, working as a reserve for the DC power source and bypassing AC currents. This can be used to reduce noise by separating different parts of the circuit, such as diverting the power line hum in audio equipment.

Pulsed power

Capacitors in the form of capacitor banks can also be used for pulsed power applications such as electromagnetic forming, pulsed lasers, particle accelerators and Marx generators. They can also be used as energy sources for detonators in nuclear weapons.

Power factor correction

Power factor correction devices use capacitors to improve energy efficiency, also known as power factor. These devices work by switching capacitors in or out of a circuit to counteract negative inefficient effects from inductive loading devices like electric motors and transmission lines. This is necessary because more power is often drawn than is required to contribute to the task.

Sensors

Capacitors react to changes in external factors, such as humidity fuel levels and mechanical strain, so they are also used in sensing applications where they measure the loss or gain of capacitance. When one of these external factors changes, a change will occur in either the distance between the capacitor’s plates or the state of the dielectric in between. Capacitors can also be used in motion detectors to aid with the device’s circuit timings.

Coupling

Because capacitors can block DC signals and pass AC signals, they can also be used to couple one section of the circuit to another. This is also known as capacitive coupling and is used in loudspeaker applications, among others, where a DC current could damage the device.

Tuning

Variable capacitors are also used in tuning circuits in radio systems. Coupled with an LC oscillator, the capacitor charges and discharges at regular intervals and, if the frequency of the intervals matches the frequency of a nearby broadcast, the radio will pick it up.

Decoupling

Another application of capacitors is to protect sensitive microchips in a circuit from noise on the power signal and to reduce the impact of electrical noise to the circuit as a whole by absorbing the noise caused by other circuit elements. These capacitors are known as decoupling capacitors and are typically located between the power supply and the ground.

Signal processing

Dynamic Random Access Memory or DRAM devices use the energy stored in capacitors to represent information in binary form. The device reads the value when the capacitor is charged, and again when it is discharged. Charge-coupled devices, or CCDs, also use capacitors to represent information but in analogue form.

Capacitors have many applications, which is why they are one of the most commonly used passive components and feature in most electronic devices we use every day.

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