Basic Knowledge of Capacitors

Capacitors are commonly used electronic components in modern circuits and devices. With a history and utility of over 250 years, capacitors are among the oldest electronic components that have been researched, designed, developed, and utilized by humans. As technology continues to advance, capacitors come in different types based on various factors. In this article, we will introduce the mainstream types of capacitors available in the market. 

What is Capacitor？

A capacitor is an unpowered component that stores electrical energy in an electric field. The capacitor is composed of two closely spaced conductors separated by a dielectric material. When the plates are connected to a power source, they accumulate charges. One plate accumulates the positive charge, while the other plate accumulates the negative charge. The electrical symbol for a capacitor is shown below:

The Formula for Capacitance

The capacitance is the ratio of charge (Q) to voltage (V), and its mathematical expression is as follows:

C = Q / V

Where:

Q is the charge measured in coulombs,

C is the capacitance measured in farads,

V is the voltage between the plates measured in volts.

Basic Unit of Capacitance

The basic unit of capacitance is the F (Farad ). Besides, capacitance is commonly expressed in subunits such as μF (microfarads), nF (nanofarads), and pF (picofarads). Since the capacitance of 1 F is relatively large, it is more common to use μF, nF, and pF units in practical applications.

Here are the specific conversions between these units:

1F＝1000000

1μF=1000nF=1000000pF

The Voltage Rating of Capacitor

Every capacitor has its voltage rating, which is one of the important parameters of a capacitor.

• The nominal voltage ratings for non-polarized capacitors include: 63V, 100V, 160V, 250V, 400V, 600V, 1000V, and so on.
• The voltage rating for polarized capacitors is relatively lower compared to non-polarized capacitors. Typical nominal voltage ratings include: 4V, 6.3V, 10V, 16V, 25V, 35V, 50V, 63V, 80V, 100V, 220V, 400V, and so on.

Classification of capacitors

Based on structure:

• Solid-state capacitors
• Variable capacitors
• Trimmer capacitors

Based on polarity:

• Polarized capacitors: Polarized capacitors are capacitors that can only be connected with a specific voltage polarity. Common types of polarized capacitors include aluminum electrolytic capacitors and tantalum electrolytic capacitors. These capacitors have a positive and negative terminal, and when connecting them, the positive terminal must be connected to the positive terminal of the power source, and the negative terminal must be connected to the negative terminal of the power source.
• Non-polarized capacitors: Non-polarized capacitors are capacitors that can be connected in any direction in a circuit. These capacitors are typically used in applications where the voltage direction needs to be changed frequently.

Common Types of Solid-state Capacitors

Ceramic Capacitors

Ceramic capacitors are considered one of the most commonly used capacitors. They use ceramic material as the dielectric, which is a good insulating material for capacitor production. Additionally, ceramic capacitors are non-polarized devices, meaning there is no need to pay attention to their positive and negative polarity. This makes the installation and use of ceramic capacitors more convenient. 

Ceramic capacitors can be classified into through-hole and surface-mount types based on their packaging. 

They can also be categorized into Class I and Class II ceramic capacitors based on the dielectric material used. Common Class I ceramics include NP0, SL0, and COG, while Class II ceramics include X7R, X5R, Y5U, and Y5V. 

Class I ceramic capacitors exhibit excellent stability with minimal variation in capacitance over temperature, voltage, and time, making them suitable for high stability and low-loss applications such as resonant circuits. 

Class II ceramic capacitors, on the other hand, have poorer capacitance stability, with significant variations over temperature, voltage, and time. They are typically used in applications where less stringent capacitance stability is required, such as filtering.

Electrolytic Capacitors

In electrolytic capacitors, a metal anode is coated with an oxide layer serving as the dielectric. These capacitors are polarized. Electrolytic capacitors are classified based on their dielectric material.

Aluminum Electrolytic Capacitors - Aluminum oxide (dielectric).

Tantalum electrolytic capacitors - Tantalum pentoxide (dielectric).

Niobium electrolytic capacitors - Niobium pentoxide (dielectric).

Applications of electrolytic capacitors

• When there is a requirement for large capacitance, electrolytic capacitors are used.
• They are used as filtering devices to reduce ripple voltage.
• They are utilized in audio amplifiers to reduce electrical noise caused by the main power source.
• Electrolytic capacitors are used to smooth input and output signals in DC signals with weak AC components.

Film Capacitors

Film capacitors are common electronic components consisting of one or multiple layers of insulating film and metal electrodes. Film capacitors can be classified based on the materials used and their structural characteristics.

Here are several common classifications of film capacitors:

• Metal Film Capacitors: Metal film capacitors use metal films as the dielectric, with common metals including aluminum, zinc, and tin. This type of capacitor offers high precision, stability, and reliability, making them widely used in various electronic devices.
• Polyester Film Capacitors: Polyester film capacitors use polyester film as the dielectric, with common polyester materials including polyethylene terephthalate (PET). These capacitors are cost-effective and suitable for low-cost applications but offer relatively lower precision.
• Polypropylene Film Capacitors: Polypropylene film capacitors use polypropylene film as the dielectric, offering low loss and excellent stability. They are typically used in high-precision and high-frequency applications, such as audio equipment and electronic filters.
• Ceramic Film Capacitors: Ceramic film capacitors use ceramic film as the dielectric, featuring high dielectric constant and low leakage current. They perform well in high-temperature and high-frequency applications and are commonly used in power filtering and energy storage circuits.
• Polyimide Film Capacitors: Polyimide film capacitors use polyimide film as the dielectric, offering high-temperature resistance and low leakage current. They are commonly used in high-temperature environments and specialized applications such as aerospace and automotive electronics.

These are common classifications of film capacitors, each with its specific characteristics and application areas. Choosing the appropriate film capacitor depends on the specific circuit requirements and performance need.

Mica Capacitors

Mica capacitors are capacitors that use natural mica as the dielectric material. A layer of metal film (usually silver) is sprayed onto the surface of the mica to serve as electrodes. The capacitors are then assembled by stacking the required capacitance value and impregnating them into a wooden case (or ceramic/plastic casing).

Mica capacitors offer several advantages, including good stability, low distributed inductance, high precision, low loss, high insulation resistance, favorable temperature and frequency characteristics, and high operating voltage range (50V to 7kV).

They are commonly used in high-frequency circuits for applications such as signal coupling, bypassing, and tuning. Common series of mica capacitors include CY, CYZ, CYRX, and others.

Paper Capacitors

Paper capacitors use specially manufactured capacitor paper as the dielectric material. Aluminum foil or tin foil is used as the electrodes, which are then wound into a cylindrical shape. The capacitor is then connected with leads, undergoes impregnation treatment, and is encapsulated in a casing or filled with epoxy resin.

The characteristics of paper capacitors include the ability to achieve high capacitance values within a small volume due to the thinness of the dielectric (generally 6-20μm) and the high tensile strength of the capacitor paper. Capacitance values can range from 1μF to 20μF. Paper capacitors have a wide capacitance range, high operating voltage, and low cost. However, they have poor chemical stability and thermal stability, are prone to aging, exhibit high dielectric losses, and are generally limited to operating temperatures below 100°C. They have high moisture absorption and require sealing, making them unsuitable for high-frequency circuit applications. Currently, low-value paper capacitors are being replaced by film capacitors.

Knowledge Popularization

What do 101 capacitor, 102 capacitor, 103 capacitor, and 104 capacitor mean?

Capacitors are commonly labeled with numbers to indicate their capacitance value, such as 103, 104, 105, and so on. These numbers represent the capacitance magnitude. The reading method is as follows:

The first two digits represent the significant figures, and the third digit represents the number of zeros (in powers of 10) to be added. The unit is picofarads (pF). Here are some examples:

A surface-mount capacitor labeled as 103 is equal to 0.01uF: that is, 10 * 10^3pF = 10nF = 0.01uF.

A surface-mount capacitor labeled as 104 is equal to 0.1uF: that is, 10 * 10^4pF = 100nF = 0.1uF.

A surface-mount capacitor labeled as 105 is equal to 1uF: that is, 10 * 10^5pF = 1000nF = 1uF.

A surface-mount capacitor labeled as 224 is equal to 0.2uF: that is, 22 * 10^4pF = 220nF = 0.2uF.

Explanation: Commonly used surface-mount capacitor labels share the same unit, which is pF. The first two digits represent X, and the last digit can be defined as Y. Therefore, the capacitance value is X * 10^Y, providing the size of the surface-mount capacitor.