What Are the Applications of Capacitors?

Capacitors serve varied roles in electronics, often related to charge storage

Collection of capacitors against a white background

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One of the most ubiquitous passive components used is the capacitor, found in nearly every electronic device ever made. Capacitors serve several essential applications in circuit design, providing flexible filter options, noise reduction, power storage, and sensing capabilities for designers.

Filter Applications

Combined with resistors, capacitors are often used as the main element of frequency-selective filters. The available filter designs and topologies are numerous and can be tailored for frequency and performance by selecting the proper component values and quality. Some of the types of filter designs include:

  • High Pass Filter
  • Low Pass Filter
  • Band Pass Filter
  • Band Stop Filter
  • Notch Filter
  • All Pass Filter
  • Equalization Filter

Decoupling/By-Pass Capacitors

Capacitors play a critical role in the stable operation of digital electronics by protecting sensitive microchips from noise on the power signal, which can cause anomalous behaviors. Capacitors used in this application are called decoupling capacitors and should be placed as close as possible to each microchip to be most effective, as all circuit traces act as antennas and will pick up noise from the surrounding environment. Decoupling and by-pass capacitors are also used in any area of a circuit to reduce the overall impact of electrical noise.

Coupling or DC Blocking Capacitors

Since capacitors have the ability to pass AC signals while blocking DC, they can be used to separate the AC and DC components of a signal. The value of the capacitor does not need to be precise or accurate for coupling, but it should be a high value, as the reactance of the capacitor drives the performance in coupling applications.

Snubber Capacitors

In circuits where a high-inductance load is driven, such as a motor or transformer, large transient power spikes can occur as the energy stored in the inductive load is suddenly discharged, damaging components and contacts. Applying a capacitor can limit, or snub, the voltage spike across the circuit, making the operation safer and the circuit more reliable. In lower-power circuits, using a snubbing technique prevents spikes from creating undesirable radio frequency interference that generates anomalous behavior in circuits and causes difficulty in gaining product certification and approval.

Pulsed Power Capacitors

At their most basic, capacitors are effectively tiny batteries that offer unique energy storage capabilities beyond those of chemical-reaction batteries. When lots of power is required in a short period of time, large capacitors and banks of capacitors are a superior option for many applications. Capacitor banks are used to store energy for applications such as pulsed lasers, radars, particle accelerators, and railguns. A common application of the pulsed-power capacitor is in the flash on a disposable camera, which is charged then rapidly discharged through the flash, providing a large pulse of current.

Resonant or Tuned Circuit Applications

While resistors, capacitors, and inductors make filters, certain combinations can also result in resonance amplifying the input signal. These circuits are used to amplify signals at the resonant frequency, create high voltage from low voltage inputs, as oscillators and as tuned filters. In resonant circuits, care must be taken to select components that can survive the voltages that the components see across them or they will quickly fail.

Capacitive Sensing Application

Capacitive sensing has recently become a common feature in advanced consumer electronics devices, although capacitive sensors have been used for decades in a variety of applications for positions, humidity, fluid level, manufacturing quality control, and acceleration. Capacitive sensing works by detecting a change in the capacitance of the local environment through a change in the dielectric—a change in the distance between the plates of the capacitor, or a change in the area of a capacitor.

Capacitor Safety

As energy storage components, capacitors can store dangerous amounts of energy that can cause fatal electrical shocks and damage equipment even if the capacitor was disconnected from power for a considerable amount of time. For this reason, it is always a good idea to discharge capacitors before working on electrical equipment.

Electrolytic capacitors are prone to fail violently under certain conditions, especially if the voltage on a polarized electrolytic capacitor is reversed. Capacitors used in high-power and high-voltage applications may also fail violently as the dielectric materials break down and vaporize.