Transistors on schematics are labeled Q followed by a reference number because of tradition. The letter could be something else, for example I have some old schematics that use T, however T is traditionally used for Transformers.
Some other traditional schematic component labels are:
- R, resistor
- C, capacitor
- L, inductor/coil
- V, vacuum tube
- U or IC, integrated circuit
- D or CR, semiconductor diode
- Z, zener diode
- M, meter or motor
- ANT, antenna
- CB, circuit breaker
- F, fuse
- RT, thermistor
- J, female connector/socket
- P, male connector/plug
- Y, crystal
- E or G, ground
- S or SW, switch
- K, relay or contactor
- B or BT, battery
- PS, power supply
- NE, neon lamp
- DS, display or lamp
In general the labels are assigned with a
mnemonicvalue, but this can't always be done so some like
Q and
Y are
arbitrary. There are official standards from IEEE, ANSI, ISO, etc. but they are often ignored.
