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.

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

• IEC 60617 (also known as 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^[1] 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• Australian Standard AS 1102 (based on a slightly modified version of IEC 60617; withdrawn without replacement with a recommendation to use IEC 60617).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 standards do not all agree, and use of unusual (even if standardized) symbols can lead to confusion and errors.^[2] Symbols usage is sometimes idiosyncratic 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.

Symbols shown are typical examples, not a complete list.^[3][4]

The shorthand for ground is GND. Optionally, the triangle in the middle symbol may be filled in.

• General ground (IEC‑style)

• Signal/low-noise ground (the asterisk is not part of the symbol)

• Chassis ground (IEC‑style)

• Battery, multi-cell

• DC voltage source

• Controlled DC voltage source

• Current source

• Controlled current source

• AC voltage source

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

• ANSI‑style: (a) Resistor, (b) Rheostat, (c) Potentiometer / Trimmer

• IEC‑style: (a) Resistor, (b) Rheostat, (c) Potentiometer / Trimmer

• • Thermistor (ANSI).^[5]
  • Use -t for NTC symbol.
  • Use +t for PTC symbol.

• General capacitor (IEC‑style); sometimes drawn with one plate curved^[2]

• Ganged (co‑moving) variable capacitors (IEC‑style)

• Trimmer variable capacitor

• Polarized capacitor (American‑style), such as electrolytic and tantalum capacitors

Optionally, the triangle in these symbols may be filled in. Note: The words anode and cathode typically aren't part of the diode symbols.

• Diac (may be a varistor in older schematics)

• Opto-isolator: LED (left), photo transistor (right)

There are many ways to draw a single-phase bridge rectifier symbol. Some show the internal diode circuit, some don't.

• Bridge rectifier

• Bridge rectifier

• Bridge rectifier

• Bridge rectifier

• Three-phase bridge rectifier

An inductor can be drawn either as a series of loops, or series of half-circles.

• Inductor symbol (series of loops)

• Air-core inductor (IEC‑style)

• Magnetic-core inductor (IEEE‑style)

• Tapped inductor (IEC‑style)

• Ferrite bead (IEEE‑style)

• Variable inductor

• Trimmer variable inductor

• Transformer with center tap on secondary winding (right side)

• Transformer with two secondary windings (right side)

• Zero-sequence current transformer (ZSCT) (also known as a window-type current transformer)

• Bushing-type current transformer

• Voltage transformer

Optionally, transistor symbols may include a circle.^[6] Note: The pin letters B/C/E and G/D/S aren't part of the transistor symbols.

• Enhancement mode, N‑channel MOSFET

• Enhancement mode, P‑channel MOSFET

• Vacuum tube tetrode
  (pin letters not part of symbol)

For multiple pole switches, a dotted or dashed line can be included to indicate two or more switch at the same time (see DPST and DPDT examples below).

• Pushbutton, normally open, push-to-make (horizontal line on top)

• Pushbutton, normally open, push-to-make (IEEE-style)

• Pushbutton, normally closed, push-to-break (IEEE-style)

• Pushbutton, normally closed, two circuits (IEEE-style)

• Switch, 1P1T, SPST (single-pole single-throw)

• Switch, 1P2T, SPDT (single-pole double-throw)

• Switch, 2P1T, DPST (double-pole single-throw)

• Switch, 2P2T, DPDT (double-pole double-throw)

• Slide switch, 1P3T,
  break-before-make, nonshorting style

• Slide switch, 1P4T,
  break-before-make, nonshorting style

• Slide switch, 1P4T,
  make-before-break, shorting style

• Rotary switch, 1P3T,
  break-before-make, nonshorting style

• Rotary switch, 1P4T,
  break-before-make, nonshorting style

• Rotary switch, 1P4T,
  make-before-break, shorting style

• Reed switch, normally open

Relays symbols are a combination of an inductor symbol and switch symbol.

Note: The pin letters in these symbols aren't part of the standard relay symbol.

• SPST, SPDT, DPST, DPDT relays (American‑style)

• SPDT relay (IEC‑style)

LED is located in diode section.

• Indicating lamp (IEEE‑style)

• Light bulb

• IEC fuse (b), equivalent symbols (a, c) (IEEE Std 315-1975)

• Molded-case circuit breaker (MCCB)

• Fuse: IEC (top) and American (lower two)

Speaker symbols sometimes include an internal inductor symbol.

• Microphone
  (IEC-style)

• General antenna
  (IEC-style)

• Dipole antenna
  (IEC-style)

• Loop antenna
  (IEC-style)

• Loop antenna
  (IEEE-style)

• Cable, Shielded 1 conductor

• Cable, 2 conductor

• Cable, Shielded 2 conductor with shield connected to ground

• Cable, 5 conductor

• Cable, Shielded 5 conductor

There are numerous connector symbol variations.

• UEXT connector based on a 5x2 shrouded header with notch key

For the symbols below: A and B are inputs, Q is output. Note: These letters are not part of the symbols.

There are variations of these logic gate symbols. Depending on the IC, the two-input gates below may have: 1) two or more inputs; 2) infrequently some have a second inverted Q output too.

The above logic symbols may have additional I/O variations too: 1) schmitt trigger inputs, 2) tri-state outputs, 3) open-collector or open-drain outputs (not shown).

• Buffer gate with schmitt trigger input

• Buffer gate with tri-state output control.
  (B is the tri-state control)

For the symbols below: Q is output, Q is inverted output, E is enable input, internal triangle shape is clock input, S is Set, R is Reset (some datasheets use clear (CLR) instead of reset along the bottom).

There are variations of these flip-flop symbols. Depending on the IC, a flip-flop may have: 1) one or both outputs (Q only, Q only, both Q & Q); 2) one or both forced inputs along top & bottom (R only, S only, both R & S); 3) some inputs may be inverted.

• Simple SR flip-flop (inverted S & R inputs)

• Gated SR flip-flop

• Gated D flip-flop (Transparent Latch)

• Clocked D flip-flop
  (Set & Reset inputs)

• Clocked JK flip-flop

• Clocked T flip-flop

Note: The outside text isn't part of these symbols.

• Spark gap for ESD discharge

The shape of some electronic symbols have changed over time. The following historical electronic symbols can be found in old electronic books / magazines / schematics, and now considered obsolete.

All of the following are obsolete capacitor symbols.

• Obsolete capacitor (very old style)

• Obsolete capacitor

• Obsolete capacitor

• Obsolete capacitor

• Obsolete capacitor

• Circuit diagram
• Reference designator
• Symbols for appliance classes

Standards

• IEC 60617 : Graphical Symbols for Diagrams; 2012.
• IEEE 315 : Graphic Symbols for Electrical and Electronics Diagrams (including Reference Designation Letters); 1975.
• U.S. DoD MIL-STD-806B : Graphical Symbols for Logic Diagrams; 1962. (RevB in 1962)

Books

• Beginner's Guide to Reading Schematics; 4th Ed; Stan Gibilisco; McGraw-Hill, 224 pages; 2018; ISBN 978-1260031119.
• How to Read Schematic Diagrams; 5th Ed; Donald Herrington; Literary Licensing; 130 pages; 2011; ISBN 978-0672224577. (4ed in 1986)(2ed in 1967)
• How to Read Electronic Circuit Diagrams; 2nd Ed; Robert Brown, Paul Lawrence, James Whitson; Tab Books; 214 pages; 1988; ISBN 978-0830628803. (2ed in 1988)
• Engineer's Mini-Notebook : Schematic Symbols, Device Packages, Design and Testing; 1st Ed; Forrest M. Mims III; Radio Shack; 48 pages; 1988. (1ed in 1988)