Transistors
A three-terminal semiconductor device used to amplify signals or act as an electronic switch.
Two types: - NPN: Current flows collector → emitter when a small base current is applied. - PNP: Current flows emitter → collector; controlled by removing base current.
Three terminals: Base (B) — control input. Collector (C) — current in (NPN). Emitter (E) — current out (NPN).
A small base current controls a much larger collector-emitter current. To use as a switch: forward-bias the base-emitter junction with sufficient base current → transistor saturates (fully ON). Remove base current → transistor cuts off (fully OFF).