Bc847 are the npn general, Purpose transistors within a compact sot23 to, 236ab, Very small sot323 sc, 70 or ultra small sot883 dfn1006, 3 surface, Mounted device smd plastic package generally built for general, Purpose switching and amplification. A transistor is a semiconductor device used to amplify or switch electronic signals and electrical power. It is made up of semiconductor material usually with at least three terminals for connection to an external circuit. A voltage or current applied to one pair of the transistor s terminals controls the current through another pair of terminals. Because the controlled output power can surpass the controlling a transistor, Input power can amplify a some transistors, Signal. Today are but many, Packaged individually more are found embedded in integrated circuits. An npn transistor comprises two semiconductor junctions that share a thin p, Doped region.