Electronic symbol

An electronic symbol is a pictogram used to represent various electrical and electronic devices or functions, such as wires, batteries, resistors, and transistors, in a schematic diagram of an electrical or electronic circuit. These symbols are largely standardized internationally today, but may vary from country to country, or engineering discipline, based on traditional conventions.

Common circuit diagram symbols (US symbols)

Standards for symbols

The graphic symbols used for electrical components in circuit diagrams are covered by national and international standards, in particular:

  • IEC 60617 (also known as British Standard BS 3939).
  • There is also IEC 61131-3 - for ladder-logic symbols.
  • JIC JIC (Joint Industrial Council) symbols as approved and adopted by the NMTBA (National Machine Tool Builders Association). They have been extracted from the Appendix of the NMTBA Specification EGPl-1967
  • ANSI Y32.2-1975 (also known as IEEE Std 315-1975 or CSA Z99-1975)
  • IEEE Std 91/91a: graphic symbols for logic functions (used in digital electronics). It is referenced in ANSI Y32.2/IEEE Std 315.
  • Australian Standard AS 1102. (Based on a slightly modified version of IEC 60617, Withdrawn without replacement with a recommendation to use IEC 60617)

The number of standards leads to confusion and errors.[1] Symbols usage is sometimes unique to engineering disciplines and national or local variations to international standards exist. For example, lighting and power symbols used as part of architectural drawings may be different from symbols for devices used in electronics.

Common electronic symbols

Symbols shown are typical examples, not a complete list.[2][3]

Traces
  • IEC-style trace junction
  • Trace crossing

Grounds

Optionally, the triangle in the following symbol may be filled in.

  • IEC-style ground (GND) symbol
  • Signal/Low noise ground (GND) symbol
  • IEC-style chassis-ground symbol

Sources
  • Battery, single cell
  • Battery, multi cell
  • Solar cell, aka Photovoltaic cell.
  • Voltage source
  • Controlled voltage source
  • Current source
  • Controlled current source
  • AC voltage source

Resistors

It is very common for potentiometer and rheostat symbols to be used for many types of variable resistors, including trimmers.

  • (a) resistor, (b) rheostat (variable resistor), and (c) potentiometer (All of them are ANSI style symbols)
  • (a) resistor, (b) rheostat (variable resistor), and (c) potentiometer (All of them are IEC style symbols)
  • Thermistor or Varistor

Capacitors
  • IEC-style capacitor, general symbol
  • Capacitor, polarized (American)
  • Capacitor, variable
  • IEC-style ganged (co-moving) variable capacitors
  • Trimmer capacitor

Diodes

Optionally, the triangle in these symbols may be filled in. There are multiple ways to draw a Bridge Rectifier symbol.

Inductors

Transformers
  • Transformer
  • Transformer with center tap on secondary winding (right side)
  • Transformer with two secondary windings (right side)
  • Current Transformer
  • Zero-Sequence Current Transformer (ZSCT) (also known as a window-type current transformer)
  • Bushing-Type Current Transformer
  • Voltage Transformer

Transistors

Unipolar

Optionally, these symbols may include a circle.

Bipolar

Optionally, these symbols may include a circle.

  • NPN bipolar junction transistor (BJT)
  • PNP bipolar junction transistor (BJT)
  • NPN Darlington
  • PNP Darlington

Vacuum tubes

Switches
  • Switch, Single Pole/Single Throw (SPST)
  • Switch, Single Pole/Double Throw (SPDT)
  • Switch, Double Pole/Double Throw (DPDT)
  • Pushbutton, Momentary or Spring-Return, make (IEEE Std 315)
  • Pushbutton, Momentary or Spring-Return, break (IEEE Std 315)
  • Pushbutton, Momentary or Spring-Return, two circuit (IEEE Std 315)

Relays
  • American-style relays, SPST, SPDT, DPST, DPDT
  • IEC relay symbol, SPDT

Lamps

Current limiters
  • IEC Fuse (b), equivalent symbols (a,c) (IEEE Std 315-1975)
  • Moulded Case Circuit Breaker (MCCB)
  • Fuse: IEC (top) and American (lower two)

Electro-acoustic devices

Antennas

Connectors

ICs
See also: Logic Gates

Miscellaneous devices

Historical electronic symbols

The shape of electronic symbols have changed over time. Some symbols were more prevalent in some countries. The following are historic electronic symbols that might be found in old electronic books and schematics.

Capacitors (historical)

See also

References
  1. Guidelines for Drawing Schematics
  2. Circuit Symbols for all Electronic Components. Talking Electronics, 2013. Retrieved 01 Apr 2015.
  3. Electrical Symbols & Electronic Symbols. RapidTables, 2012. Retrieved 17 April 2016.

Further reading
  • Beginner's Guide to Reading Schematics; 4th Ed; Stan Gibilisco; McGraw-Hill, 224 pages; 2018; ISBN 978-1260031119.
  • How to Read Electronic Circuit Diagrams; 2nd Ed; Brown, Lawrence, Whitson; Tab Books; 214 pages; 1988; ISBN 978-0830628803.
  • How to Read Schematic Diagrams; 4th Ed; Donald Herrington; Sams Publishing; 160 pages; 1986; ISBN 978-0672224577. (2nd Ed in 1973)
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