Capacitors are found in nearly every electronic device, and serve several essential applications in circuit design. Capacitors provide flexible filter options, noise reduction, power storage, and sensing capabilities for designers, among other uses.
In this guide, we take a look at the variety of capacitor uses in electronic products and equipment.gethinlane / Getty Images
What Are Capacitors Used For?
Combined with resistors, capacitors are often used as the main element of frequency-selective filters. The available filter designs and topologies are numerous. These can be tailored for frequency and performance by selecting the proper component values and quality. The types of filter designs include:High Pass FilterLow Pass FilterBand Pass FilterBand Stop FilterNotch FilterAll Pass FilterEqualization Filter
Decoupling and By-Pass Capacitors
Capacitors play a critical role in the operation of digital electronics by protecting sensitive microchips from noise on the power signal. This noise can cause abnormal behaviors. Capacitors used in this application are called decoupling capacitors. These capacitors should be placed close to each microchip to be effective because circuit traces act as antennas and 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
Capacitors can pass AC signals while blocking DC and can be used to separate the AC and DC components of a signal. The value of the capacitor doesn't need to be precise or accurate for coupling. However, it should be a high value, as the reactance of the capacitor drives the performance in coupling applications.
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. This discharge can damage 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. Using a snubbing technique in lower-power circuits prevents spikes from creating undesirable radio frequency interference. This interference generates anomalous behavior in circuits and causes difficulty in gaining product certification and approval.
Pulsed Power Capacitors
Capacitors are small 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 store energy for applications such as pulsed lasers, radars, particle accelerators, and rail guns. A common application of the pulsed-power capacitor is in the flash on disposable cameras, 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 result in resonance amplifying the input signal. These circuits amplify signals at the resonant frequency, create a high voltage from low voltage inputs, and are used as oscillators and tuned filters. In resonant circuits, care must be taken to select components that can survive the voltages that each component sees across it, or it will quickly fail.
Capacitive Sensing Application
Capacitive sensing has recently become a common feature in advanced consumer electronics devices. However, capacitive sensors have been used for decades in various 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.
As energy storage components, capacitors can store dangerous amounts of energy. This high level of energy can cause fatal electrical shocks and damage equipment even when a capacitor is 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.