The Ultimate Guide to Capacitor Symbols

Capacitors are crucial in modern technology, found in nearly every electronic device. They store the energy from an electric current. According to Precedence Research, the global capacitor market is projected to reach $61.83 billion by 2032. Capacitors are available in various shapes and sizes, each serving a specific purpose, so choosing the right one is vital. Different symbols in circuit diagrams represent them, each indicating unique properties and meanings. The performance and reliability of a capacitor depend on its selection and use in the circuit. Therefore, understanding capacitor symbols is essential for electronics professionals. These symbols provide key information such as the capacitor type, capacitance, voltage rating, and other critical details. Understanding these symbols is essential for choosing the right capacitor for your electronic circuits. This article provides an overview of the capacitor symbol. Every detail you need to know about it.

What is a Capacitor?

A capacitor, also known as a condenser, is an electronic component that stores and releases electrical energy. Its primary function is to store and release electrical charge, making it a versatile component in electronic circuits.

Capacitors are typically made of an insulating material called a dielectric, sandwiched between two conductive plates, usually made of metal. The dielectric material can be air, ceramics, polyester film, aluminum electrolyte, etc. One plate is connected to the positive electrode of the circuit, and the other is connected to the negative electrode. When a voltage is applied to the capacitor, a positive charge builds up on one plate, and a negative charge builds up on the other. This charge is stored in the dielectric, creating an electric field.

Overview of Capacitor Symbol

The capacitor symbol in a circuit diagram represents the physical capacitor element. It is typically depicted as two parallel lines or plates, symbolizing the two conductive plates in an actual capacitor. These plates are separated by a non-conductive substance known as a dielectric.

The parallel lines can be drawn vertically or horizontally in circuit diagrams. One of the lines may be curved for polarized capacitors, such as electrolytic capacitors, or the plus "+" symbol is used on the positive side.

The symbol does not depict the actual physical layout of the component. Still, it helps understand its function - storing and releasing electrical charge - and how it is connected to the circuit. When you encounter this symbol in a circuit diagram, it indicates the presence of a capacitor in that part of the circuit.

Significance of Capacitor Symbol in Electrical Diagrams

The capacitor symbol consistently represents capacitors in electrical schematics and circuit designs. This symbol provides essential information about the circuit's capacitor's type, value, and polarity. Engineers and technicians can understand the capacitor's function and characteristics without physically inspecting the component. Standardized capacitor symbols in circuit diagrams help designers and manufacturers communicate effectively and consistently.

Why Should We Need to Understand Capacitor Symbols?

Electronics professionals and enthusiasts must understand capacitor symbols for several reasons:

1. They aid in selecting the correct capacitor for a circuit based on its type, value, and polarity.

2. They ensure the capacitor is correctly placed in the circuit, essential for optimal performance and reliability.

3. Capacitor symbols are necessary for interpreting circuit diagrams and building and troubleshooting electronic circuits.

Electronics professionals and enthusiasts must grasp capacitor symbols.

Types of Capacitor Symbols

Polarized Capacitor Symbols

Polarized capacitors, such as electrolytic capacitors, have distinct positive and negative polarity on their two pins, which cannot be reversed during use. They typically filter out noise or interference signals in circuits, earning them the nickname "smooth filter capacitors." Electrolytic capacitors come in two common types based on their material: aluminum electrolytic capacitors and tantalum electrolytic capacitors.

Non-polarizedized Capacitor Symbols

Unlike their polarized counterparts, non-polarized capacitors do not have a positive or negative polarity on their two pins. This means the two pins can be interchanged and connected in any direction during use.

Non-polarized capacitors, also known as fixed capacitors, have a fixed capacitance value determined by the material and production process. They are commonly used for circuit coupling, smoothing, filtering, phase shifting, and resonance functions.

Various non-polarized capacitors exist, including colored ring capacitors, paper capacitors, porcelain dielectric capacitors, mica capacitors, polyester capacitors, glass glaze capacitors, and polystyrene capacitors. While their circuit symbols are identical, their physical shapes and characteristics differ.

Variable Capacitor Symbol

A variable capacitor allows manual adjustment of its capacitance value, commonly used in tuning circuits like those in radios. Its symbol resembles that of a fixed capacitor but includes an arrow through one of the plates to indicate adjustability. The symbol is represented as follows:

Fixed Capacitor Symbols

The symbol for a fixed capacitor is typically represented by two parallel horizontal lines with a space between them.

Film Capacitor Symbols

Film capacitors consist of two conducting plates separated by a thin plastic or polymer film and are known for their stability, low loss, and reliability in electrical circuits. Their symbols in circuit designs vary depending on their construction and features.

In circuit diagrams, film capacitors are typically represented by a rectangle with rounded corners featuring a straight line on one end for the positive terminal. The negative terminal of the rectangle is represented by a curved line or the absence of a line, resembling symbols used for other fixed capacitors.

1. Polyester, Polypropylene, Polystyrene, and Other Film Capacitors

These capacitors use thin plastic dielectrics, providing stability, low losses, and durability, making them popular in various electrical circuits.

Mylar capacitors: Comprising a thin polyester sheet with metal electrodes on both sides, these capacitors are cost-effective and commonly used in audio circuits, power supplies, and general applications.

Polypropylene capacitors: Utilizing thin polypropylene films with metal electrodes on both sides, these capacitors offer superior stability and lower losses than polyester capacitors, making them suitable for high-frequency applications like filters and tuning circuits.

Polystyrene capacitors: These capacitors feature thin polystyrene films with metal electrodes on both sides. They are known for their exceptional stability and low losses, albeit being more expensive and less common.

Polyphenylene sulfide (PPS) and polytetrafluoroethylene (PTFE) film capacitors: PPS capacitors offer excellent temperature stability, while PTFE capacitors excel in high-frequency applications.

2. Metalized Film Capacitors

Metalized film capacitors use a thin plastic film as the dielectric and a metal coating on one or both sides as electrodes. This design provides stability, minimal losses, and reliability, making them suitable for various applications based on their capacitance, voltage, and temperature ranges.

3. Mica, Glass, and Other Fixed Capacitor Symbols

These capacitors, known for their stability and durability, are used in circuits where precision is crucial, such as oscillators, filters, and resonant circuits.

Mica capacitors: These consist of thin mica sheets with metal electrodes on both sides. They are stable and low-loss, making them ideal for high-frequency applications like RF, filters, and high-precision timing circuits.

Glass capacitors: Ceramic capacitors with metal electrodes, these capacitors are suitable for high-capacitance applications due to their high dielectric constant. They are commonly used in power supply decoupling circuits and applications requiring high capacitance and stability.

Electrolytic Capacitor Symbol

The symbol for an electrolytic capacitor is typically represented by two parallel lines or a straight line and a curved line, as shown in the image.

Bipolar Capacitor Symbol

The symbol for a bipolar capacitor is similar in structure to that of a non-polar capacitor, indicating that it can be connected to a circuit in either direction.

Polymer Capacitor Symbols

1. Aluminum Polymer Capacitors

Aluminum polymer capacitors use conductive polymers instead of liquid or gel electrolytes. Compared to traditional electrolytic capacitors, they are more stable, reliable, and resistant to temperature and aging. Aluminum polymer capacitors offer better capacitance and longevity.

2. Tantalum Polymer Capacitors

Tantalum polymer capacitors also utilize conductive polymers instead of liquid or gel electrolytes. They are known for their stability, reliability, and resistance to temperature and aging. Tantalum polymer capacitors outlast traditional tantalum electrolytic capacitors and provide higher capacitance.

3. Non-polarized Electrolytic Capacitor Symbols

Non-polarized electrolytic capacitors are designed to be connected in any direction in circuits where the polarity is unknown or may change. Their symbol reflects this non-polarized nature.

Variable and Trimmer Capacitor Symbols

Electronic circuits utilize trimmers and variable capacitors for precise frequency tuning. The symbols for these capacitors vary based on their construction and features.

Variable capacitors are typically depicted as a rectangle with two parallel lines, one representing the stationary plate and the other the movable plate. An arrow pointing towards the movable plate indicates that changing the plate's position alters the capacitance.

Variable Capacitor Symbols

A variable capacitor is a capacitor whose capacitance value can be manually adjusted. These capacitors, such as those found in radios, are commonly used in tuning circuits. The symbol for a variable capacitor is similar to that of a fixed capacitor, but it includes an arrow through one of the plates to indicate adjustability. The symbol is represented as follows:

Trimmer Capacitor Symbols

A commonly used symbol for a trimmer capacitor is two parallel lines with a diagonal line in between, indicating its adjustable nature.

Specialized Capacitor Symbols

Electronic circuits utilize a variety of specialized capacitors, each represented by unique symbols in circuit diagrams depending on their construction and features. It's crucial to use the correct symbol for each type of capacitor to ensure proper circuit design and assembly.

1. Supercapacitor (Ultracapacitor) Symbols

Supercapacitors, also known as ultracapacitors, store and release energy rapidly. Their circuit symbol typically consists of two parallel lines with a curved line connecting them, representing their ability to store energy. Some symbols may include positive and negative signs to indicate polarity. Supercapacitors find applications in electric vehicles, renewable energy systems, and electronics requiring high power and rapid charge/discharge cycles. Proper selection and installation are essential, considering capacitance, voltage rating, and other characteristics to prevent damage.

2. Motor Run and Start Capacitor Symbols

Motor run and start capacitors enhance torque and performance in single-phase electric motors. Proper selection based on capacitance, voltage, and other characteristics is critical for ensuring motor performance and reliability.

3. Feedthrough Capacitor Symbols

Electronic circuits use feedthrough capacitors to reduce electromagnetic interference (EMI) and noise. They block low-frequency transmissions and provide low-impedance paths for high-frequency signals. Correct selection and installation, considering capacitance, voltage rating, and other parameters, are vital for effective EMI suppression.

4. Light Emitting Capacitor (LEC) Symbols

Light-emitting capacitors (LECs) utilize electroluminescent polymers (ELPs) in their active layers to emit light when an electric current passes through. Due to their chemical and electrical properties, conjugated polymers in LECs can act as ionic conductors and semiconductors.

5. Silicon Capacitor Symbols

Silicon capacitors with reverse-biased p-n junction dielectrics are used in tuning and RF circuits. Proper selection based on capacitance range, voltage rating, and other parameters is crucial for RF and tuning applications.

Surface Mount and Leaded Capacitor Symbols

Electronic circuits utilize both surface-mount and leaded capacitors. Leaded capacitors have leads for circuit connection, while surface-mount capacitors are mounted directly onto circuit boards.

In circuit designs, surface-mount capacitors are depicted as rectangles with metal pads. These pads indicate where the capacitor should be soldered onto the circuit board. Capacitance values may be printed on the capacitors or shown in circuit diagrams.

Before selecting a capacitor, it's important to consider the type and the specific needs of the circuit. Surface-mount and leaded capacitors have advantages and disadvantages, making them suitable for different applications.

Voltage-Dependent Capacitor Symbol

Regarding voltage-dependent capacitors, a common symbol includes a standard capacitor symbol with an arrow or a curved line pointing into it, denoting its voltage dependency.

Temperature-Dependent Capacitor Symbol

Add a temperature coefficient symbol to the standard capacitor symbol to symbolize a temperature-dependent capacitor. This coefficient indicates how the capacitance changes with temperature.

Tuning Capacitor Symbol

Symbols for capacitors used in tuning circuits, essential for radio frequency applications, are specific to their role and aid engineers in designing effective tuning circuits.

AC Capacitor Symbol

The symbol for an AC capacitor typically consists of a pair of parallel lines representing the capacitor's plates, with a curved line or squiggle connecting them. This curved line indicates that the capacitor is intended for AC circuits.

DC Capacitor Symbol

The symbol for a DC capacitor is similar, but it may lack the curved line or squiggle. It consists of two parallel lines representing the plates without the additional feature used to signify AC.

Mylar Capacitor Symbol

Like other capacitors, the symbol for a Mylar capacitor is a basic representation used in electronic circuit diagrams. It typically consists of two parallel lines representing the plates of the capacitor without any polarity markings. Mylar capacitors are a type of film capacitor.

Capacitor Symbol Meaning

The symbol used in electronic circuit diagrams to represent a capacitor holds specific meanings and provides information about the capacitor's characteristics.

Parallel Lines:

The two parallel lines in the capacitor symbol represent the capacitor's conductive plates. When a voltage is applied across them, these plates store electrical charge.

Curved Line (or Squiggle):

The curved line or squiggle connecting the plates indicates that the capacitor is designed for AC (alternating current) circuits. It represents the alternating nature of the current in AC circuits.

Polarity (if applicable):

Some capacitor symbols may include polarity markings, indicating the orientation of the capacitor in the circuit. For polarized capacitors (such as electrolytic capacitors), one plate is positive and negative. The positive side is typically marked with a "+" sign.

No Curved Line (for DC Capacitors):

The symbol may lack the curved line in the case of DC (direct current) capacitors or unpolarized capacitors. This signifies that the capacitor is intended for use in DC circuits.

Capacitor Symbols on a Multimeter

The capacitance symbol on a multimeter is typically represented by the letter "F," which stands for Farads, the unit of capacitance. Some multimeters may also use a symbol resembling the capacitor symbol used in circuit diagrams (two parallel lines), although this is less common.

To measure capacitance, set the multimeter dial to the setting with the capacitor symbol. Next, connect the probes to the capacitor you're measuring, ensuring proper polarity if the capacitor is polarized. The multimeter display will then show the capacitor's capacitance in Farads (or often in microfarads, µF).

How a Multimeter Measures Capacitance

A multimeter measures capacitance by charging a capacitor with a known current, measuring the resulting voltage, and then calculating the capacitance using the formula C=Q/V, where Q is the charge stored in the capacitor, and V is the voltage across the capacitor. This process is automated within the multimeter.

Variations in Capacitor Symbols

Differences in American and European Symbols

In circuit diagrams, capacitor symbols can vary slightly between American and European standards.

• American: In American notation, a fixed (non-polarized) capacitor is typically represented by two parallel lines. Like an electrolytic capacitor, a polarized capacitor is often represented by a plus "+" symbol on the positive side or a curved line representing the negative plate and a straight line representing the positive plate.

• European: In European notation, a fixed (non-polarized) capacitor is usually represented by a straight line and a curved line parallel to each other, while a polarized capacitor maintains the same representation as in American notation.

Other International Variations

In other parts of the world, the capacitor symbols used may follow American or European conventions or sometimes a mix of both. It's also not uncommon to see the symbol of a variable capacitor (an arrow through one of the plates) used to represent a generic capacitor in some regions. Always refer to the legend or key in the circuit diagram to understand the symbols used.

How to Read Capacitor Symbols?

1. Know the Units of Measurement

Capacitance is measured in Farads (F), but in practice, capacitors are typically rated in smaller units such as microfarads (μF), nanofarads (nF), or picofarads (pF). Familiarize yourself with these units to interpret the values correctly.

2. Find the Capacitance

Numerical digits represent the capacitance value on the capacitor symbol. Look for a number that indicates the capacitance value, which may be followed by a letter code indicating the unit of measurement.

3. Search for Tolerance Value

All capacitors have a tolerance that specifies the maximum allowable deviation from the stated capacitance value. This tolerance is represented by a percentage or a code on the symbol. The tolerance values can be anything, such as ±5%, ±10%, ±20%, or more. For instance, if you find "104K" on the symbol, the letter "K" represents a tolerance of ±10%.

4. Find the Voltage Rating

Capacitors also have a voltage rating, indicating the maximum voltage they can safely handle. The voltage rating is usually represented as a number followed by a unit such as volts (V) or kilovolts (kV). For instance, if you see "25V" on the symbol, the capacitor can handle a maximum voltage of 25 volts.

5. Look for a Positive or Negative Sign

Some capacitors, particularly polarized electrolytic and tantalum capacitors, have a polarity. They must be connected in the correct direction, or they may fail or even explode. The positive and negative terminals are indicated on the symbol using different markings, such as a plus sign (+) or a minus sign (-).

How to Draw the Capacitor Symbol?

The drawing method of the capacitor symbol is quite simple: it generally consists of two horizontal lines and two parallel vertical lines. Different types of capacitors may have slightly different symbols, but the basic structure remains the same.

The horizontal lines at both ends indicate that the two pins of the capacitor are connected to other circuits to form an electronic circuit.

The two parallel lines represent a capacitor in an electronic circuit diagram, embodying its internal principle.

How to Classify the Circuit Symbols of Capacitors in the Circuit?

The symbols used to represent capacitors in circuits are typically categorized based on their general type or function. Here are the common classifications for capacitor symbols:

1. Fixed Capacitors: These capacitors have a specific capacitance value determined during manufacturing. The symbols for fixed capacitors generally depict their basic shape and type without indicating specific capacitance values. Examples include ceramic, film, and electrolytic capacitors. The symbols can vary slightly depending on the specific type but generally reflect the overall shape of the capacitor. Common fixed capacitor symbols include:

2. Variable Capacitors: These have adjustable capacitance values, also known as tuning capacitors or trimmers. They are used in applications where capacitance needs adjustment or fine-tuning. The symbol for a variable capacitor typically includes additional components like a mechanical dial or a set of curved lines to indicate adjustability. Common variable capacitor symbols are:

3. Polarized Capacitors: This specific type has positive and negative terminals and must be connected in the correct polarity for proper operation. Examples include electrolytic and tantalum capacitors. The symbol for polarized capacitors includes polarity indicators like a straight line and a curved or plus-shaped line representing the positive and negative terminals. Common polarized capacitor symbols are:

It's important to refer to the documentation or specifications of the specific capacitor to ensure the correct circuit symbol is used for that type. These symbols serve as standardized representations to aid in circuit design and understanding the connections and characteristics of capacitors in the circuit.

How to Distinguish the Positive and Negative Poles of Electrolytic Capacitors?

First, let's understand how to identify the positive and negative terminals of conventional electrolytic capacitors.

Snap-in Capacitor

Another method is to check the embossing on the capacitor contacts. The negative terminal often features various embossings, while some manufacturers mark the positive and negative terminals on the contacts.

Screw Terminal Capacitor

Another way is to examine the silver lace. The one marked with a '–' indicates the negative pole. Additionally, inspect the screw terminals on the top; most manufacturers label the positive and negative poles.

Chip Aluminum Electrolytic Capacitors

This is best identified by the end with the black half, which indicates the negative pole.

Conclusion

A capacitor is a fundamental component found in nearly all electronic devices. It is available in various types, such as variable, tantalum, film, and more. Each type is represented by unique symbols in circuit diagrams, aiding engineers and technicians in identifying the capacitor type and its application. Understanding term symbols involves knowledge of the capacitance measurement unit, voltage rating, and other factors.

Exploring capacitors and their applications can be rewarding for those interested in electronics. Start by experimenting with different capacitors in simple circuits, reviewing datasheets to understand their electrical properties, and gradually incorporating them into more complex circuits.

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