Basics of Capacitor: Capacitor Symbols

What is a Capacitor?

 

A capacitor is an electronic component widely used in various electrical and electronic circuits. It is designed to store and release electrical energy, acting as a temporary reservoir or “energy buffer” within a circuit. Compared to a typical battery, a capacitor can store very small amounts of energy, such as 10,000 times smaller, which is still useful for many devices and circuits.

 

It is made up of two conducting plates and a dielectric, which is an insulating substance. An electric field forms across the dielectric when a voltage is applied between the plates, which causes an electrical charge to build up. Main purpose of types of capacitors is to store charge. Electrons build up on one plate of a capacitor when it is linked to a power source, while an opposite but equal charge builds up on the other plate. The surface area, spacing, and kind of dielectric material all affect how much charge a capacitor can hold. The unit of measurement for this is farads (F). 

 

 

 

Purpose of Capacitor Symbol in Electrical Schematics & Diagrams

 

 

 

Types of Capacitors You should know

 

Type of Capacitor	Subcategories	Description
Ceramic Capacitors	Class 1: NP0, C0G Capacitor	Very stable, minimal change in capacitance with temperature. Used in timing and precision applications.
	Class 2: X7R Capacitor	Good stability, suitable for bypass and decoupling applications over a wider temperature range.
	Class 2: Y5V Capacitor	High capacitance value, significant capacitance change with temperature. Used where size and cost are critical.
	Class 2: Z5U Capacitor	Used for bypass and decoupling; not suitable where tight capacitance tolerance is needed.
Electrolytic Capacitors	Aluminum Electrolytic	High capacitance, polarized. Ideal for power supply filters and audio amplifiers.
	Tantalum Electrolytic	Higher stability and reliability than aluminum, polarized. Used in medical and military applications.
	Niobium Electrolytic	Similar to tantalum, cost-effective, and used in various electronic applications.
Film Capacitors	Polyester Film (Mylar)	Good dielectric strength, used in coupling and decoupling applications.
	Polypropylene Film (PP)	Excellent electrical properties, used in high-frequency and power applications.
	Polystyrene Film (PS)	Low cost, high stability, used in filters and timing circuits.
	Polyethylene Naphthalate (PEN)	High temperature and frequency performance, suitable for demanding environments.
Super Capacitors	Double-layer (EDLC)	Used for rapid charge and discharge cycles such as in-memory backup systems.
	Pseudo Capacitors	Combines capacitor-like and battery-like properties for energy storage and high-power applications.
Variable Capacitors	Air Variable	Manually adjustable, used in radio tuning and frequency adjustment.
	Trimmer Capacitors	Small, variable capacitors for device tuning during manufacturing or in-field adjustments.
	Vacuum Variable	High voltage, stable tuning applications, used in high power and radio frequency systems.

 

How to Read Capacitor Symbols?

 

You should be able to read a capacitor symbol to understand electronic circuit diagrams and schematics. Here’s the procedure to do so:

 

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. The number 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 Capacitor Works?

 

As we all know, metals are made of positively and negatively charged particles which make them neutral. However, when an electric field is applied, the electrons from the positive plate or side will start moving toward the negative plate. However, the dielectric between both plates doesn’t allow the electrons to pass through, resulting in electron accumulation on one plate. 

 

The capacitor stores electrical energy in the form of the accumulated charge on its plates. The amount of charge stored is directly proportional to the applied voltage and the capacitance of the capacitor. The equation is given as follows:

 

• Q = CV relates the charge (Q) stored in the capacitor to the capacitance (C) and voltage (V) applied. 

 

When the capacitor is connected to a circuit, such as a load or another component, it can release the stored energy. This is known as discharging. 

 

Applications

 

Here are some applications of a capacitor: 

• Energy storage in power supply circuits to provide a stable source of energy.

• Coupling and decoupling capacitors block DC and allow AC signals to pass.

• Filtering and smoothing of electrical signals to remove noise and ripples.

• Motor starting and phase-shifting in electric motors and HVAC systems.