Introduction to Electronic Schematic Symbols
Electronic schematics are visual representations of electrical circuits and components, providing essential information to understand how a circuit functions. By using standardized symbols, engineers and technicians can easily communicate and interpret these diagrams.
Schematic symbols can be broadly categorized into three main groups: passive components, active components, and electromechanical components. Each group consists of several subcategories, featuring components that perform specific tasks or have unique properties.
In this section, we will delve into the world of electronic schematic symbols, exploring their origins, standardization, and conventions. We will discuss the roles of international organizations, such as the International Electrotechnical Commission (IEC) and the Institute of Electrical and Electronics Engineers (IEEE), in creating and maintaining the standards for these symbols.
Additionally, we will explore the differences between US and IEC symbols and the importance of adhering to these standards for efficient communication and collaboration within the field of electronics.
Common Electronic Components and Their Symbols
Passive Components
Passive components are essential elements in electronic circuits that do not generate energy but instead store, dissipate, or regulate it. Unlike active components, which can amplify or control the flow of current, passive components primarily respond to the electrical signals they receive without adding energy to the circuit.
The three main types of passive components are resistors, capacitors, and inductors. Each of these components serves a distinct purpose within a circuit:
- Resistors: Resistors limit the flow of current and help in voltage division within a circuit. They provide a predefined amount of resistance to the flow of electrical current, allowing for precise control of voltage and current levels. Resistors come in various forms, such as fixed resistors, variable resistors, thermistors, and photoresistors, each with its specific function and application.
- Capacitors: Capacitors are capable of storing electrical energy in the form of an electric field. They can charge and discharge rapidly, making them useful in various applications, such as smoothing voltage fluctuations, filtering out electrical noise, and storing energy for short periods. Capacitors come in different types, including ceramic, electrolytic, and tantalum capacitors, each with its unique characteristics and use cases.
- Inductors: Inductors store energy in the form of a magnetic field created by the flow of electrical current through a coil of wire. They oppose changes in current flow, making them valuable for filtering high-frequency signals, energy storage, and electromagnetic interference (EMI) reduction. Inductors can be found in various forms, such as air-core, iron-core, and ferrite-core inductors, each with its specific properties and applications.
Resistors
Resistors are used to limit the flow of current and divide voltage in a circuit. They are denoted by a zigzag line or a rectangle.
| Schematic Symbol | Symbol ID | Symbol Description |
|---|---|---|
 | Fixed Resistor (IEEE Design) | A fixed value resistor whose resistive value is indicated next to its schematic symbol |
 | Fixed Resistor (IEC Design) | A fixed value resistor whose resistive value is indicated next to its schematic symbol |
 | Potentiometer (IEEE Design) | Three terminal variable resistance whose resistive value is adjustable from zero to its maximum value |
 | Potentiometer (IEC Design) | Three terminal variable resistance whose resistive value is adjustable from zero to its maximum value |
 | Rheostat (IEEE Design) | Two terminal fully adjustable rheostat whose resistive value varies from zero to a maximum value |
 | Rheostat (IEC Design) | Two terminal fully adjustable rheostat whose resistive value varies from zero to a maximum value |
 | Thermistor (IEEE Design) | Thermal resistor whose resistive value changes with changes in surrounding temperature |
 | Thermistor (IEC Design) | Thermal resistor whose resistive value changes with changes in surrounding temperature |
Capacitors
Capacitors store electrical energy in the form of an electric field. They are represented by two parallel lines or a combination of one straight line and one curved line.
| Schematic Symbol | Symbol ID | Symbol Description |
|---|---|---|
 | Fixed Value Capacitor | A fixed value parallel plate non-polarized AC capacitor whose capacitive value is indicated next to its schematic symbol |
 | Fixed Value Capacitor | A fixed value parallel plate non-polarized AC capacitor whose capacitive value is indicated next to its schematic symbol |
 | Polarized Capacitor | A fixed value polarized DC capacitor usually an electrolytic capacitor which must be connected to the supply as indicated |
 | Variable Capacitor | An adjustable capacitor whose capacitance value can be varied by means of adjustable plates |
Inductors
Inductors store energy in a magnetic field created by the flow of current. They are represented by a series of curved or looped lines.
| Schematic Symbol | Symbol ID | Symbol Description |
|---|---|---|
 | Open Inductor | An open inductor, coil or solenoid that generates a magnetic field around itself when energized |
 | Iron Core Inductor | An inductor formed by winding the coil around a solid laminated iron core indicated by solid lines |
 | Ferrite Core Inductor | An inductor formed by winding the coil around a non-solid ferrite core indicated by dashed lines |
Active Components
Active components can control the flow of current and amplify signals. They include diodes, transistors, and integrated circuits.
Diodes
Diodes allow current to flow in one direction while blocking it in the opposite direction. They are represented by a triangle pointing to a vertical line.
| Schematic Symbol | Symbol ID | Symbol Description |
|---|---|---|
 | Semiconductor Diode | Semiconductor pn-junction diode used for rectification and high current applications |
 | Zener Diode | Zener diode used in its reverse voltage breakdown region for voltage limiting and regulation applications |
 | Schottky Diode | Schottky diode consisting of an n-type semiconductor and metal electrode junction for low voltage applications |
Transistors
Transistors are used to amplify or switch electronic signals. There are two main types: Bipolar Junction Transistors (BJT) and Field-Effect Transistors (FET). Each type has its unique symbol.
| Schematic Symbol | Symbol ID | Symbol Description |
|---|---|---|
 | NPN Bipolar Transistor | Lightly doped p-type base region between two n-type emitter and collector regions with the arrow indicating direction of conventional current flow out. |
 | PNP Bipolar Transistor | Lightly doped n-type base region between two p-type emitter and collector regions. Arrow indicates direction of conventional current flow in. |
 | Darlington Pair Transistor | Two bipolar transistor npn or pnp connected in a series common collector configuration to increase current gain |
 | N-JFET Transistor | N-channel junction field effect transistor having an n-type semiconductive channel between source and drain with the arrow indicating direction of conventional current flow |
 | P-JFET Transistor | P-channel junction field effect transistor having a p-type semiconductive channel between source and drain with the arrow indicating direction of conventional current flow |
 | N-MOSFET Transistor | N-channel metal-oxide semiconductor field effect transistor with an insulated gate terminal which can be operated in depletion or enhancement mode |
 | P-MOSFET Transistor | P-channel metal-oxide semiconductor field effect transistor with an insulated gate terminal which can be operated in depletion or enhancement mode |
Electromechanical Components
Electromechanical components convert electrical energy into mechanical energy or vice versa. They include switches, relays, and motors.
Switches
Switches are used to open or close a circuit, controlling the flow of current. They come in various forms, such as push-button, toggle, and slide switches, each with its distinct symbol.
| Schematic Symbol | Symbol ID | Symbol Description |
|---|---|---|
 | SPST Toggle Switch | Single-pole single-throw toggle switch used for making (ON) or breaking (OFF) a circuits current |
 | SPDT Changeover Switch | Single-pole double-throw changeover switch used for changing the direction of current flow from one terminal to another |
 | Pushbutton Switch (N.O) | Normally open contacts pushbutton switch – push to close, release to open |
 | Pushbutton Switch (N.C) | Normally closed contacts pushbutton switch – push to open, release to close |
 | DIP Switch Assembly | PCB mounted DIP switch with 1-to-10 toggle switches either single-pole, double-pole, rotary or with a common terminal |
Relays
Relays are electromechanical switches that use an electromagnet to open or close a circuit. They are denoted by a rectangle enclosing a coil and switch symbols.
| Schematic Symbol | Symbol ID | Symbol Description |
|---|---|---|
 | SPST Relay Contacts | Electromechanical relay with internal single-pole single-throw toggle contacts |
 | SPDT Relay Contacts | Electromechanical relay with internal single-pole double-throw changeover contacts |
 | DPST Relay Contacts | Electromechanical relay with internal double-pole single-throw toggle contacts |
 | DPDT Relay Contacts | Electromechanical relay with internal double-pole double-throw changeover contacts |
US and IEC Schematic Symbols
Differences and the Importance of Standards
While both standards aim to provide a common language for electronic schematics, some differences exist between the symbols used in each. Understanding these differences and adhering to the respective standards is essential for efficient communication and collaboration within the field of electronics.
Key Differences between US and IEC Symbols
While many symbols are consistent across both US and IEC standards, some components have different representations in each system. Some of the key differences include:
- Resistors: In US schematics, resistors are depicted as a zigzag line, whereas IEC schematics represent them as a rectangle.
- Inductors: US symbols for inductors feature curved lines, while IEC symbols use looped lines.
- Ground Connections: The US standard uses a variety of symbols for ground connections, while the IEC standard typically employs a single, downward-pointing arrow symbol.
- Logic Gates: Although both standards use similar symbols for logic gates, IEC symbols typically include a distinctive rectangular outline around the gate symbol.
Importance of Adhering to Standards
Maintaining consistency with schematic symbol standards is crucial for several reasons:
- Effective Communication: Adhering to a common set of symbols ensures that engineers, technicians, and enthusiasts can easily interpret and understand circuit diagrams, regardless of their country of origin or background.
- Reduced Errors: Using standardized symbols minimizes the risk of misunderstandings or misinterpretations, leading to fewer errors in the design, construction, and troubleshooting of electronic circuits.
- Increased Efficiency: Standardized symbols streamline the process of sharing and collaborating on electronic designs, as individuals can quickly grasp the layout and function of a circuit without needing to decipher unfamiliar symbols.
- Enhanced Learning: By learning and adhering to a standardized set of symbols, students and professionals can easily access and benefit from a wealth of resources, such as textbooks, online tutorials, and industry publications, furthering their understanding and expertise in electronics.
Understanding basic electronic circuit schematic symbols is essential for anyone involved in the world of electronics. These standardized symbols enable effective communication and interpretation of electronic schematics, providing a solid foundation for designing, troubleshooting, and repairing circuits.
This comprehensive guide has covered the most common electronic components and their respective schematic symbols, including passive, active, and electromechanical components. By mastering these symbols, you’ll be well-equipped to excel in your electronics projects and pursuits.
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FAQ
What are the most common electrical symbols?
The most common symbols used in electrical schematic diagrams include symbols for components such as resistors, capacitors, diodes, transistors, transformers, and integrated circuits, as well as symbols for power sources, switches, connectors, and ground.
What is the standard for electrical schematic symbols?
The standard for electrical schematic symbols varies depending on the location and application. In the United States, the National Electrical Manufacturers Association (NEMA) publishes a set of standardized symbols in their publication ANSI/NEMA Standard Publication No. 31-1998. In Europe, the International Electrotechnical Commission (IEC) publishes a set of symbols in their publication IEC 60617.
What are three types of schematic diagram?
One-line diagrams: These diagrams show the connections between electrical components in a simplified manner, typically using only single lines to represent the conductors and symbols to represent the components.
Block diagrams: These diagrams use blocks to represent components and lines to show the connections between them. They are useful for showing the overall layout and function of a system.
Wiring diagrams: These diagrams show the physical connections between components, using symbols to represent the components and lines to show the wiring connections.
How many schematic symbols are there?
The number of schematic symbols varies depending on the application and the standards used. However, there are thousands of standard symbols that have been developed for use in electrical schematic diagrams, ranging from basic components to complex integrated circuits. It is important to consult the relevant standards for the specific application to ensure that the correct symbols are used.