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10 Commonly Used Circuit Board Components

circuit board components


The history of components used in the circuit goes back to the late 1900s and has been shaped by continuous development and new innovations with the advancement in technology. PCBs were made from materials like Bakelite, Masonite, cardboard sheets and a thin wooden plank in olden days. Invention of passive components like resistor, capacitor and inductor were done during the 19th century. Later on in the 20th century vacuum tubes were introduced and transistors replaced these bulky vacuum tubes. With all the developments on the components and circuit boards, introduction of Integrated circuits (IC’s) revolutionized the electronic industry by enabling compact sized components and devices.

In the 1980s surface mount technology (SMT) was introduced which further reduced the circuit board components size and made assembly process easier. With the introduction of microcontrollers and microprocessor IC’s in 1970-1980, capability of electronic devices were improved and went to a whole new level. In today’s world of electronic industry surface mount devices (SMD) has become a standard technology. Over the several years, evolution of components has enabled the PCB to bring down the size to miniature level without losing the electrical performance and has helped to develop more efficient and powerful devices that are used worldwide.


Printed circuit boards (PCBs) are the heart of any modern electronic device which provides mechanical support for electronic components. With the evolution of components used in circuit boards over several years, it is essential for everyone involved in PCB design, manufacturing and the assembly process to understand the characteristics of the components better. In this article, let us understand a few of commonly used components in the circuit board industry and their applications, functions and the importance of using those in electronic devices.

Classification of Circuit Board Components

Circuit board components are classified based on the functionality, construction and the characteristics. There are mainly 3 types of circuit board components:

Passive Components

Components that do not require any external power source to operate are called passive components. These components are used in controlling, filtering the signals and to store energy. Few examples of passive components are resistor, capacitor, inductors and so on.

Active Components

Components that require external sources to operate are called active components. These circuit board components rely completely on the external source to perform the functionalities. Few examples of active components are transistors, op-amps and diodes.

Integrated Circuits

Integrated circuits are semiconductor devices that have multiple active and passive components integrated onto a single chip. It has a wide range of functions which includes memory storage, processing the signal, performing logical operations and many more. They are different types of IC’s such as analog, digital and mixed-signal.

Detailed Information of Circuit Board Components

Now, let us understand the importance and uses of circuit board components deeply by exploring each and every circuit board component below.


It is a passive component which opposes the flow of electric current in the circuit. They are used to control the flow of electric current, limiting the voltage level and as voltage divider in various circuits. It is measured in ohms (Ω). The value of resistance varies from a few ohms to several megaohms.

It is denoted by the schematic symbol as shown below:


Schematic Symbol of Resistor

Schematic Symbol of Resistor

There are different types of resistors, to name such as

  • Fixed resistor
  • Variable resistor
  • Thermistors
  • Light dependent resistors


It is a passive circuit board component which stores and releases energy in the form of an electric field. It has two conducting plates separated by a vacuum or by any insulating material known as dielectric. Capacitors are used in circuits to store energy, filter the unwanted noises, to regulate the voltage level and also act as decoupling capacitors. Capacitance is measured in Farads(F). The value of capacitance varies from picofarads(pf) to farads(F), depending upon the construction and size.

It is denoted by schematic symbol as shown below:


 Schematic Symbol of Capacitor

Schematic Symbol of Capacitor

There are different types of capacitors namely:

  • Fixed capacitors
  • Variable capacitors
  • Polarized capacitors


These are passive circuit board components which store the energy in the form of a magnetic field when an electric current flows through it. The coil around the core generates a magnetic field when an electric current is passed through the coils. It is used in circuits for various purposes like choking, impedance matching, attenuating or filtering the noise, and for storing energy in converters. Inductance is measured by Henry(H). Greater the inductance, greater is the amount of energy stored. It is denoted by schematic symbol as shown below:

Schematic Symbol of Inductor

Schematic Symbol of Inductor

There are different types of Inductors namely:

  • Air-core inductors
  • Ferromagnetic-core inductors
  • Toroidal inductors


Diodes are two terminal semiconductor devices that allow the flow of current in one direction and blocks in opposite directions. They are used in circuits for rectification, voltage regulation, switching purposes and also for power surge protection. It is denoted by schematic symbol as shown below:

Schematic Symbol of Diodes

Schematic Symbol of Diodes

There are different types of diodes designed for different applications, few of them are:

  • Zener diode
  • Light emitting diode
  • Schottky diode
  • Photodiode


It is a three terminal semiconductor device used for amplification and switching of the signals. Transistors are the backbone of today’s electronic devices as they have enabled the miniaturization of circuit boards with the development of advanced technologies. It consists of semiconductor materials like silicon and germanium.

It is denoted by the schematic symbol as below:

Schematic Symbol of Transistor

Schematic Symbol of Transistor

Two main types of transistors:

  • Bi-polar Junction Transistor (BJT)
  • Field Effective Transistor (FET)

Furthermore these BJT’s are divided into 2 types: NPN & PNP transistors.

FET is divided into 2 types: Junction field effect transistor (JFET) and Metal-oxide-semiconductor Field effect transistor (MOSFET)

Operational Amplifier (Op-amps)

Op-amp is the integrated circuit (IC) that amplifies the voltage between two different input voltages. They are used in circuits for processing the signals, voltage amplification and filtering also. It consists of two input terminals namely Inverting input (-) and Non-inverting input (+). If the input is provided to the inverting terminal, output voltage will be 180 degree out of phase with the input signal. If the signal is provided to a non-inverting terminal, output will be in phase with the input signal.

It has high input impedance, high gain and low output impedance which makes it better to use in various electronic circuits. It is denoted by the schematic symbol as shown below:

Schematic Symbol of Op-amps

Schematic Symbol of Op-amps


Circuit board components that produce the periodic waveforms typically sinusoidal, square and triangular which work on the principle of oscillations are called oscillators. They are used in various electronic devices for generating frequency, clock generation, generating signals and in timing circuits.

There are several types of oscillators based on their design and applications, few of them are listed below:

  • RC oscillator
  • LC oscillator
  • Crystal oscillator
  • Voltage controlled oscillator
  • Colpitts oscillator
  • Wein bridge oscillator …etc.
Schematic Symbol of Oscillators

Schematic Symbol of Oscillators


Relay is an electrical switch that controls the flow of electrical current in the circuit. They are used in circuits for switching high current flow, to provide isolation and also for remote control purposes. There are mainly two types of relays:

  • Electromechanical relay
  • Solid state relay (SSRs)


Components that detect and respond to any physical triggers in the environment and convert them to electrical signals which can be used to analyze the data by electronic systems. The inputs from the environment can be factors like temperature, pressure, light and motion.

Sensors are classified into several types based on the environmental parameters, few of them are listed below based on their sensing capacity:

  • Temperature sensor
  • Pressure sensor
  • Light sensor
  • Humidity sensor
  • Proximity sensor
  • Fluid flow sensor
  • Biosensor


It is the circuit board component used to provide electrical connection between other circuit board components and external devices. They are used to transfer data, signals, power and electronic signals to enable the connection between devices. Few of the common connector types are as follows:

  • Board to board connector
  • Circular connector
  • Fiber optic connectors
  • USB connectors
  • Coaxial connectors


Component used to make or break the connection between two conductive paths is called a switch. They are used to control the power , signal routing, etc. choosing the kind of switch required purely depends on the kind of application and operating conditions of the equipment.

Some of the common types of switches used based on their applications are:

  • Pushbutton switch
  • Toggle switch
  • Slide switch
  • DIP switch
  • Rotary switch
Schematic Symbol of Switches

Schematic Symbol of Switches


The device which transfers electrical energy between two or more circuits with the help of electromagnetic induction is known as a transformer. They are used in circuits mainly to step up or step down the voltage inputs and to provide the power uniformly. It works on the principle of Faraday’s law of mutual induction. It consists of primary at input stage and secondary winding at the output circuit. When current is passed through the primary input, magnetic flux is generated around the windings which result in the generation of electric current induced in the secondary output terminal. The induced current can be varied by varying the number of windings on the secondary terminal to step-up or step-down the voltage level between the input & output circuit.

It is denoted by schematic symbol as shown below:

Schematic Symbol of Transformer

Schematic Symbol of Transformer


They are types of integrated circuits (IC), which contain processor, memory locations, and many input / output peripherals on a single chip. It is used to control and manage the operations of various electronic devices with the help of programs. They are cost-effective and are commonly used in applications such as consumer electronics, medical devices, IOT devices and industrial instruments.

Some of the most common types of microcontroller based on the application, performance and architectural design are as follows:

  • 8-bit/16-bit/32-bit/64-bit microcontrollers
  • Low power microcontroller
  • System-on-chip microcontroller


As the name itself says, it is a processor which has a central processing unit (CPU) mounted on a single chip. It can execute instructions, perform arithmetic and logical operations and many more. They are mainly used in computers, tablets, laptops, smartphones and embedded systems.

They are classified into different types based on the architecture, performance and the kind of application it is intended to do. Few of them are listed below:

  • Complex instruction set computing (CISC) microprocessors
  • Reduced instruction set computing (RISC) microprocessors
  • General purpose microprocessor
  • Embedded microprocessor


It is a device which converts chemical energy to electrical energy through chemical reactions. They are used in circuit boards to provide a reliable and uninterrupted power source to the devices.

Batteries are divided into different types based on performance parameter, applications and the characteristics they possess, some of the common types are listed below:

  • Alkaline battery
  • Lithium-ion (Li-ion) battery
  • Lead-acid battery
  • Nickel-cadmium (Nicd) battery
  • Lithium-polymer (LIPO) battery


It is a safety device used to protect the circuit, when an excess current flows through it. It safeguards the circuit board components from getting damaged due to excess flow of current and avoids possible fire catching. When current is more than the rated current value of fuse, it will melt down the wire and cause an open circuit which results in stopping the current flow to the circuit. They are used in power supplies, motors, and many more electronic appliances.

Different types of fuses are listed below:

  • Surface mount fuse
  • Cartridge fuse
  • Thermal fuse
  • Resettable fuse
  • Blade fuse


These are the circuit board components that are used widely and very frequently in the circuit board industry all over the world to produce an error free electronic product. Selection of appropriate components purely depends on the kind of application, environmental parameters, characteristics of the components and many more. It is very crucial to select the correct circuit board components in order to make the product reliable and durable.

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