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Solid state devices • Crystal diodes – a crystal and a bronze wire • Semiconductors – made from poor conductors with conductive impurities – Poor conductors = silicon and germanium – Impurities = • “P” substances with a shortage of electrons • “N” substances with excess electrons Solid state diode BARRIER REGION N P Solid state diode BARRIER REGION N P Solid state diode BARRIER REGION N P Solid state diode Junction transistor • Transfer + Resistance = Transistor • Made up of “sandwich” of PNP or NPN materials Junction transistor N P N Junction transistor collector base emitter Junction transistor Solid state devices • Junction transistor – “junction” refers to the junction between materials – where voltage appears. – Current amplifier (tubes are voltage amps) • Field effect transistor – “FET” is a low power high impedance device • Silicone controlled rectifier – “SCR” controls current flow – used in varispeed and dimmer Solid state devices • Zener diode – allows output voltage to be fixed for use in power supply Solid state –v- vacuum tube Solid state • Efficient (little heat) • Infinite lifespan • Compact • Physically rugged • Low power ouput • Low impedance Vacuum tube • Requires and produces heat • Finite lifespan • Large • Delicate • High power output • High impedance Transistors Printed circuit Printed circuit Integrated circuit