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.

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 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Australian Standard AS 1102 (based on a slightly modified version of IEC 60617; withdrawn without replacement with a recommendation to use IEC 60617).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.

Common electronic symbols

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

Traces

Grounds

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)

Sources

Battery, single-cell
Battery, multi-cell
Solar (photovoltaic) cell

DC voltage source
Controlled DC 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 and trimmers.

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

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

Capacitors

General capacitor (IEC‑style); sometimes drawn with one plate curved^[2]
Variable capacitor
Ganged (co‑moving) variable capacitors (IEC‑style)
Trimmer variable capacitor
Polarized capacitor (American‑style), such as electrolytic and tantalum capacitors

Diodes

Optionally, the triangle in these symbols may be filled in, or a line may be drawn through the triangle (less desirable). The words anode and cathode aren't part of the diode symbols. For instructional purposes, sometimes two letters (A/C or A/K) are placed next to diode symbols similar to how the letters C/B/E or D/G/S are placed next to transistor symbols. "K" is often used instead of "C", because the origin of the word cathode is kathodos, and to avoid confusion with "C" for capacitors in silkscreen of printed circuit boards.

Diode (rectifier)
Schottky diode
Zener diode
Transient voltage suppression (TVS) diode. Top symbol is directional, bottom is bidirectional.
Light emitting diode (LED)
Photodiode
Tunnel diode
Varicap
Shockley diode
Silicon controlled rectifier (SCR)
Diac (may be a varistor in older schematics)
Constant-current diode
Opto-isolator: LED (left), photo transistor (right)

Bridge rectifiers

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

Inductors

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

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

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.

Bipolar

Unipolar

N-channel junction gate field-effect transistor (JFET)
P-channel junction gate field-effect transistor (JFET)
Metal–oxide–semiconductor field-effect transistor (MOSFET)
Enhancement mode, N‑channel MOSFET
Enhancement mode, P‑channel MOSFET

Vacuum tubes

Vacuum tube diode
Vacuum tube triode
Vacuum tube tetrode
(pin letters not part of symbol)
Vacuum tube pentode

Switches

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

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)

Lamps

LED are located in the diode section.

Neon lamp
Indicating lamp (IEEE‑style)
Incandescent lamp
Indicatory incandescent light bulb
Light bulb

Current limiters

IEC fuse (b), equivalent symbols (a, c) (IEEE Std 315-1975)
Molded-case circuit breaker (MCCB)
Fuse: IEC (top) and American (lower two)

Electro-acoustic devices

Speaker symbols sometimes include an internal inductor symbol.

Loudspeaker
(IEEE-style)
Buzzer
(IEC-style)
Microphone
(IEEE-style)
Microphone
(IEC-style)

Antennas

General antenna
(IEC-style)
Dipole antenna
(IEC-style)
Loop antenna
(IEC-style)
Loop antenna
(IEEE-style)

Cables

Cable, Shielded 1 conductor
Cable, 2 conductor
Cable, Shielded 2 conductor with shield connected to ground
Cable, 5 conductor
Cable, Shielded 5 conductor

Connectors

There are numerous connector symbol variations.

TRS phone jacks
UEXT connector based on a 5x2 shrouded header with notch key

ICs

Logic gates

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)

Flip-flops

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

OpAmps

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

Operational amplifier (opamp)
Comparator

Oscillators

Crystal oscillator (IEEE‑style)
Ceramic resonator (3 pins)

Miscellaneous devices

Hall-effect sensor
Gas-discharge tubes (GDT) for ESD discharge
Spark gap for ESD discharge

Historical electronic symbols

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.

Capacitors (historical)

All of the following are obsolete capacitor symbols.

Obsolete capacitor (very old style)
Obsolete capacitor
Obsolete capacitor
Obsolete capacitor
Obsolete capacitor

References

^ "IEEE Standard American National Standard Canadian Standard Graphic Symbols for Electrical and Electronics Diagrams (Including Reference Designation Letters)," in IEEE Std 315-1975 (Reaffirmed 1993), vol., no., pp.i-244, 1993, doi:10.1109/IEEESTD.1993.93397.
^ ^a ^b Sobering, Tim (April 2008). Guidelines for Drawing Schematics.
^ Circuit Symbols for all Electronic Components. Talking Electronics, 2013. Retrieved 01 Apr 2015.
^ Electrical Symbols & Electronic Symbols. RapidTables, 2012. Retrieved 17 April 2016.
^ "Standards for Resistor Symbols". EePower. EETech Media. Retrieved September 13, 2021.
^ "A4.11 Envelope or Enclosure". ANSI Y32.2-1975 (PDF). Archived from the original (PDF) on 2022-10-09. Retrieved 2020-12-29. The envelope or enclosure symbol may be omitted from a symbol referencing this paragraph, where confusion would not result

External links

[1] "IEEE Standard American National Standard Canadian Standard Graphic Symbols for Electrical and Electronics Diagrams (Including Reference Designation Letters)," in IEEE Std 315-1975 (Reaffirmed 1993), vol., no., pp.i-244, 1993, doi:10.1109/IEEESTD.1993.93397.

[Sobering-2] Sobering, Tim (April 2008). Guidelines for Drawing Schematics.

[3] Circuit Symbols for all Electronic Components. Talking Electronics, 2013. Retrieved 01 Apr 2015.

[4] Electrical Symbols & Electronic Symbols. RapidTables, 2012. Retrieved 17 April 2016.

[5] "Standards for Resistor Symbols". EePower. EETech Media. Retrieved September 13, 2021.

[6] "A4.11 Envelope or Enclosure". ANSI Y32.2-1975 (PDF). Archived from the original (PDF) on 2022-10-09. Retrieved 2020-12-29. The envelope or enclosure symbol may be omitted from a symbol referencing this paragraph, where confusion would not result

[1]

[2]

[3]

[4]

[5]

[6]