Capacitor Basics

What is a capacitor?

With the ability to store electrical charge, block DC signals, and pass AC signals capacitors are play a pivotal role in electronic circuits.
As such they are used for backup (battery), decoupling (reduce noise), and coupling (remove DC bias voltage).
At type of passive component like resistors and inductors (coils), capacitors are used in everything from smartphones, wearables, and data centers to base stations, industrial equipment, and automotive systems.
Although the term capacitor is common in most parts of the world, in Japan it's often referred to as a condenser.

Structures and Features of Different Capacitors

Capacitors come in various types, but the basic structure consists of an insulator (dielectric) sandwiched between electrodes, capable of storing charge when a voltage is applied.
Actual products include single-layer, trench, multilayer, electrolytic, and wound types.
Capacitors can be differentiated by the following characteristics depending on the dielectric and electrode materials used.
Polarity, small/large size, thin/low-profile, operating temperature range, capacitance size, rated voltage range, high-frequency performance, capacitance stability, presence/absence of noise due to piezoelectric effects, etc.
Therefore, when selecting a capacitor, it is necessary to understand the characteristics of each type.

[Types and Characteristics of Different Capacitors】

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		Silicon Capacitor	Multilayer Ceramic Capacitor		Tantalum Capacitor		Aluminum Electrolytic Capacitor
Capacitor Appearance
Electrode ①		Doped silicon	Nickel		Tantalum (anode)		Aluminum (anode)
Dielectric		Silicon oxide or Silicon nitride	Temperature compensating ceramic	High dielectric constant ceramic	Tantalum pentoxide		Aluminum oxide
Electrode ②		Doped silicon	Nickel		Manganese dioxide (cathode)	Conductive polymer (cathode)	Electrolyte (cathode)	Conductive polymer (cathode)
Polarity		No	No		Yes		Yes
Compact		◎	◎	◎	〇	〇	×	×
Thin/Low Profile		◎	〇	〇	△	△	×	×
Operating Temperature Range		◎	〇	〇	〇	〇	△	〇
Large Capacitance		△	×	〇	〇	〇	◎	◎
High Rated Voltage		〇	◎	◎	〇	〇	◎	△
High Insulation Resistance (Low Leakage Current)		◎	◎	◎	〇	△	〇	△
High Frequency Characteristics		◎	〇	〇	×	△	×	△
Capacitance Stability	DC Bias	◎	◎	×	◎	◎	◎	◎
	Temperature	◎	◎	×	〇	〇	×	〇
High Reliability		◎	〇	〇	×	△	×	△
Noise (Ringing)		No	Yes		No		No
Advantages		Compact Low profile Good high frequency characteristics High operating temp High capacitance stability High Reliability High EMI immunity(can include TVS protection element) No noise since no piezoelectric effects	Compact Good high frequency characteristics High capacitance stability	Compact Good high frequency characteristics	Large capacitance in a compact size High capacitance stability	Large capacitance in a compact size High capacitance stability Lower ESR and higher allowable ripple current than manganese dioxide products	Large capacitances Broad lineup	Large capacitances High capacitance stability Lower ESR and higher allowable ripple current than electrolytic products
Disadvantages		Small capacitances Limited lineup	Small capacitances Ringing noise generated due to piezoelectric effect Prone to cracking during substrate partitioning and temperature changes	Low capacitance stability Ringing noise generated due to piezoelectric effect Prone to cracking during substrate partitioning and temperature changes	Failure in short mode Polarized	Failure in short mode Polarized	Large product size Short lifespan due to liquid leakage Polarized	Large product size Polarized

◎: Excellent 〇: Very Good △: Average ×: Poor

About Capacitance

Capacitance is a typical characteristic of a capacitor.
And is generally expressed by the following formula.
Capacitance=ε_r×ε₀×S/d
（ε_r：Relative permittivity of the dielectric, ε₀：Permittivity of a vacuum =8.9×10^-12[F/m], S：Electrode surface area, d：Dielectric thickness）

As the above equation shows, capacitance is proportional to the surface area of the electrode and dielectric constant of the dielectric and inversely proportional to the dielectric thickness.
Relative permittivity is an inherent value of the dielectric material used.
The unit of capacitance is F (farad), and in practice pF (picofarad), nF (nanofarad), uF (microfarad), mF (millifarad), etc. are commonly used.
（ 10^-12[F]=1pF, 10^-9[F]=1nF, 10^-6[F]=1[μF], 10^-3[F]=1[mF] ）

Capacitor Applications

Capacitors (including tantalum) are often used in the following applications.

Backup (Battery)

Utilizing as a battery

When the load current increases due to power supply interruption or a sudden rise in IC drive speed, the line voltage from the power supply may drop, possibly causing IC malfunction. To prevent this, charge stored in a capacitor is supplied to the IC, temporarily maintaining the line voltage.

Decoupling

Utilizing AC characteristics

To supply stable DC voltage, capacitors are used to remove high-frequency noise caused by high-speed circuit drive or externally induced noise superimposed on the power supply line. Adopted in general power supply circuits.

Coupling

In this application, the capacitor removes the DC bias voltage from the previous stage and only passes through the AC signal voltage.

Typically adopted in audio circuits.

What is a Tantalum Capacitor?

Tantalum is a metal, whose name is derived from Tantalus, an anti hero from Greek mythology.
Generally, surface mount tantalum capacitors are constructed by forming electrodes at both ends of the tantalum element using a lead frame, then sealing the structure with mold resin.

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