Electronic Component Schematic Symbols

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3 months ago

Electronic Component Schematic Symbols

When creating new electronics, designers, and engineers must have a common language to describe the components that go into the new project. This language comes in electronic component schematic symbols that unambiguously describe a component’s position, type, and function within a project.

Experienced designers may only need text descriptions of components if they have a reliable memory for electronic component schematic symbols. Schematic symbols can vary slightly depending on the area of the world in which they are found, and designers need to be aware that multiple symbols may mean the same thing. There is a wide variety of electronic component schematic symbols, with this article only covering the most common symbols.

What is an Electronic Component Schematic Symbol?

An electronic component schematic symbol is a pictorial representation of an electronic component, usually standardized by an international electronics industry body. Such standards organizations include:

International Electrotechnical Commission: IEC 60617 – Graphical Symbols for Diagrams. The IEC database requires a yearly subscription, but designers can access one of the most comprehensive groups of schematic symbols relied upon by engineers worldwide. Most designers and manufacturers use this standard directly or base their own standards on it.
IEEE/ANSI 315-1975 – IEEE Standard for Graphic Symbols for Electrical and Electronics Diagrams (Including Reference Designation Letters). This common graphical standard for schematics symbols was deprecated in 2019, but many of its symbols are still in common usage, so engineers would be wise to reference it. Designers can access it with a one-time purchase.
IPC-2612-1: Sectional Requirements for Electronic Diagramming Symbol Generation Methodology. This IPC standard defines strategies for creating new schematic symbols that comply with electronics industry norms. It’s accessible through a one-time purchase.

Historically, CAD librarians needed to memorize many of these symbols or refer to industry reference literature when creating or cataloging components. Today, they are widely available on many reputable websites, along with design footprints and schematics.

Schematic symbols include a wide variety of component types and circuit features. Most people who have seen simple electrical diagrams are familiar with symbols for resistors, switches, fuses, and other passives. However, electronic component symbols can involve more complex circuit features, such as batteries with single or multiple cells, inductors, capacitors, and transformers.

There are even schematic symbols for some simple machines that may be integrated into a circuit, like buzzers, speakers, relays, and motors. With extremely complex machines, it may be unnecessary, too time-consuming, or too difficult to depict all the components they contain within a schematic. Therefore, schematic symbols can simplify designers’ projects by using a single symbol for complex machines.

Table of Schematic Symbols

It’s important for designers to know many of these older schematic symbols if they are upgrading or analyzing older technology. If a designer or engineer creates completely new electronics projects, knowledge of older symbols is not as essential but may be beneficial occasionally. Given the rapid increase of technology, the new IPC standard governing the creation of new schematic symbols may be especially helpful to designers.

If there are two symbols present for a given component, the first symbol is the international variant, while the second is the United States variant. The symbols shown below follow the IEEE/ANSI specifications, as these are most commonly used in schematic editors in ECAD software. However, many designers and some open-source ECAD programs use the IEC symbols or a mix of the IEEE/ANSI symbols. Due to the popularity of the IEEE/ANSI symbols in major ECAD platforms, they are listed here for reference.

Electronic Component Schematic Symbols
Name	Symbol	Details
AC Power Supply		Provides alternating current on a circuit board Similar to the DC power supply symbol
Ammeter		Measures electric current in amperes Used for either AC or DC circuits
Amplifier (Operational) / Op-Amp		An integrated circuit that amplifies weak signals Amplifies and outputs the difference in voltage between its two inputs
Amplifier (Voltage)		Increases the output signal in a circuit
Battery		Source of electrical energy Batteries of made of multiple battery cells
Battery Cell		A single cell of a battery
Branching Box		Point of connection between multiple elements of a circuit node The junction of wires for a single net
Capacitor (Non-Polarized)		Components that store energy Connections are interchangeable between the two pins
Capacitor (Polarized / Electrolytic)		A capacitor that must be connected with the correct polarity between the two pins
Capacitor (Variable)		The amount of capacitance can be adjusted Available as user adjustable, or factory pre-set
Cathode Ray Oscilloscope / CRO		A device that compares input signals to time or another signal
DC Power Supply		Provides direct current on a circuit board Similar to the AC power supply symbol
DC Power Supply (Variable)		Provides direct current on a circuit board, but the output can be adjusted
Diode (Junction)		A semiconductor that allows current to only flow in one direction Used for switching and isolation
Diode (Light Emitting) / LED		A diode that emits light Unlike standard light bulbs, LEDs are polarized and must be connected correctly
Diode (Photo)		A diode that produces current from light that strikes it Used as photo detectors and sensors
Diode (Zener)		Like a regular diode, the backwards flow of current is blocked until it reaches a specific level called the Zener voltage Zener diodes are very useful for voltage regulation
Diode Bridge		A module of diodes connecting four to six diodes in a single package Useful for rectifying alternating current (AC) into direct current (DC)
Electrical Appliance		Represents devices controlled through the PCB Can include TVs, security cameras, etc.
Filament Bulb		A standard (non-diode) light bulb
Fuse		A safety device that protects circuits from excessive current
Galvanometer		A device used to detect and measure the magnitude of minute amounts of current
Inductor		Inductors filter high-frequency noise in circuits by opposing sudden changes in current Also known as chokes or coils
Integrated Circuit / IC		Electronic circuits integrated on one piece of semiconductor material Also known as ICs or chips ICs contain miniaturized transistors and other components
Logic Gate (AND)		An electrical device (gate) used in integrated circuits The output of the AND gate is true only if both input signals are true
Logic Gate (OR)		An electrical device (gate) used in integrated circuits The output of the OR gate is true if one or both input signals are true
Logic Gate (XOR)		An electrical device (gate) used in integrated circuits The output of the OR gate is true only if one of the input signals are true
Loudspeaker		Output device producing sound driven by the circuit board
Microphone		Input device capturing sound for the circuit board
Motor		Electromechanical engine driven or controlled by signal outputs from the circuit board
Multiple Conductor Line		A group of wires represented by one single wire on the schematic Also known as a bus
Potentiometer / Voltage Divider		Resistors that control the flow of current through settings that can be varied Potentiometers, or pots, are three-terminal devices
Resistor		A passive component that restricts the flow of current in a circuit One of the most commonly used parts
Resistor (Light Dependent) / LDR		Current resistance decreases as light intensity increases Used to detect light levels for security lighting systems, etc.
Resistor (Thermal) / Thermistor		Current resistance changes with temperature fluctuations Used in temperature monitoring systems
Resistor (Variable)		A standard resistor whose value of resistance can be altered
Socket Outlet (Telecom Indication)		Sockets used for telecom applications Microphone, speaker, telephone, etc.
Socket Outlet (TV and Radio Aerial)		Sockets used for antenna connections TV, radio, etc.
Transformer (Iron-Cored)		Devices that alter system voltage The two coils may be illustrated in different sizes to represent a step-up or step-down transformer
Transformer (Iron-Cored, 2 Secondary Windings)		The multiple secondary windings allow this transformer to produce different output voltages
Transistor (NPN)		Basic semiconductor device that amplifies or switches signals NPN transistors switch on with the presence of a high signal.
Transistor (N-Type Junction Field Effect) / NJFET		This device uses input voltage to control the current flowing through it NJFETs have a backward flow of current through them
Transistor (PNP)		Basic semiconductor device that amplifies or switches signals PNP transistors switch on with the presence of a low signal
Transistor (P-Type Junction Field Effect) / PJFET		This device uses input voltage to control the current flowing through it PJFETs have a forward flow of current through them
Voltmeter		Used to measure voltage of electrical circuitry between two locations

PCB Designers Need Complete Libraries with Schematic Symbols

Today’s ECAD tools generally include most or all of the symbols shown above in their built-in libraries. In addition, most designers don’t refer to one of the standards listed above when adding schematic symbols to a component library. Instead, the most common components are called out with a specific designator prefix (R = resistor, C = capacitor, L = inductor, U = integrated circuit). A schematic symbol will frequently be provided with a note describing the part number or type of component for the designer. As long as the schematic symbol contains the appropriate designator prefix or is a self-explanatory symbol, many designers will not worry about which standard the symbol follows.

The schematic symbol must match the pinout shown in the component datasheets for integrated circuits and connectors and then be added to a component library with PCB footprints and 3D models. Instead of creating every component from scratch, PCB designers can use the best electronic parts search engine to find the component data they need, including sourcing data, specifications, and datasheets for components.

If you’re looking for CAD models for electronic component schematic symbols, Ultra Librarian helps by compiling all your sourcing and CAD information in one place.

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