Sur un schéma, le symbole graphique indique non seulement le type de composant, mais aussi le sens de circulation du courant. On distingue deux grandes familles : Transistors - SparkFun Learn Transistors - SparkFun Learn NPN VS PNP Transistor Symbols
Common emitter, common base, or common collector, which determine how the transistor amplifies or switches signals. If you'd like, I can: Explain the difference between NPN and PNP symbols.