Editing Amplifier (section)

===Power amplifiers===
{{See also|Audio power amplifier| RF power amplifier}}
{{Unreferenced section|date=December 2024}}
[[File:Sagem VS4 - Skyworks SKY77328-13-9827.jpg|thumb|Power amplifier by [[Skyworks Solutions]] in a [[Smartphone]].]]

A power amplifier is an amplifier designed primarily to increase the power available to a [[Electrical load|load]]. In practice, amplifier power gain depends on the source and load [[Electrical impedance|impedances]], as well as the inherent voltage and current gain. A [[radio frequency]] (RF) amplifier design typically optimizes impedances for power transfer, while audio and instrumentation amplifier designs normally optimize input and output impedance for least loading and highest signal integrity. An amplifier that is said to have a gain of 20&nbsp;dB might have a voltage gain of 20&nbsp;dB and an available power gain of much more than 20&nbsp;dB (power ratio of 100)—yet actually deliver a much lower power gain if, for example, the input is from a 600&nbsp;Ω microphone and the output connects to a 47&nbsp;[[Ohm|kΩ]] input socket for a power amplifier. In general, the power amplifier is the last 'amplifier' or actual circuit in a signal chain (the output stage) and is the amplifier stage that requires attention to power efficiency.

Audio power amplifiers are typically used to drive [[loudspeaker]]s. They will often have [[Stereophonic sound|two output channels]] and deliver equal power to each. An RF power amplifier is found in radio [[transmitter]] final stages. A [[Servo drive|servo motor controller]] amplifies a control voltage to adjust the speed of a motor, or the position of a motorized system.

Power amplifier circuits (output stages) are classified as A, B, AB and C for [[analog circuit|analog]] designs—and class D and E for switching designs. The [[power amplifier classes]] are based on the proportion of each input cycle (conduction angle) during which an amplifying device passes current.<ref>{{Cite web|url=http://electronicdesign.com/analog/understanding-amplifier-operating-classes|title=Understanding Amplifier Operating "Classes"|website=electronicdesign.com|access-date=2016-06-20|date=2012-03-21}}</ref> The image of the conduction angle derives from amplifying a sinusoidal signal. If the device is always on, the conducting angle is 360°. If it is on for only half of each cycle, the angle is 180°. The angle of flow is closely related to the amplifier [[Electrical efficiency|power efficiency]].{{Cn|date=December 2024}}