Editing Transistor (section)

===Transistor as an amplifier===
[[File:NPN common emitter AC.svg|thumb|An amplifier circuit, a common-emitter configuration with a voltage-divider bias circuit]]
The [[common-emitter amplifier]] is designed so that a small change in voltage (''V''<sub>in</sub>) changes the small current through the base of the transistor whose current amplification combined with the properties of the circuit means that small swings in ''V''<sub>in</sub> produce large changes in ''V''<sub>out</sub>.<ref name="Pulfrey" />

Various configurations of single transistor amplifiers are possible, with some providing current gain, some voltage gain, and some both.

From [[mobile phone]]s to [[television]]s, vast numbers of products include amplifiers for [[sound reproduction]], [[Transmitter|radio transmission]], and [[signal processing]]. The first discrete-transistor audio amplifiers barely supplied a few hundred milliwatts, but power and audio fidelity gradually increased as better transistors became available and amplifier architecture evolved.<ref name="Pulfrey" />

Modern transistor audio amplifiers of up to a few hundred [[watt]]s are common and relatively inexpensive.