class AB amplifier
class AB amplifier[‚klas ¦ā¦bē ′am·plə‚fī·ər]
An amplifier in which the grid bias and alternating grid voltages are such that anode current in a specific tube flows for appreciably more than half but less than the entire electric cycle.
A transistor amplifier whose operation is class A for small signals and class B for large signals.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
amplifier classesAnalog amplifiers are cataloged by how much current flows during each wave cycle. Measured in degrees, 360º means current flows 100% of the time. The more current, the more inefficient and the more heat generated. See amplifier.
Class A ANALOG
The amplifier conducts current throughout the entire cycle (360º). The Class A design is the most inefficient and is used in low-power applications as well as in very high-end stereo. Such devices may be as little as 15% efficient, with 85% of the energy wasted as heat.
Class B ANALOG
The current flows only 180º for half the cycle, or two transistors can be used in a push-pull fashion, each one operating for 180º. More efficient than Class A, it is typically used in low-end products.
Class AB ANALOG
Combines Class A and B and current flows for 180º to 200º. Class AB designs are the most widely used for audio applications. Class AB amplifiers are typically about 50% efficient.
Class C ANALOG
Operating for less than half of one wave cycle (100º to 150º), Class C amplifiers are the most efficient, but not used for audio applications because of their excessive distortion.
Class G ANALOG
A variation of the Class AB design that improves efficiency by switching to different fixed voltages as the signal approaches them.
Class H ANALOG
An enhancement of the Class G amplifier in which the power supply voltage is modulated and always slightly higher than the input signal.
|The red indicates how much of the time current is flowing through one wave cycle.|
Class D DIGITAL
Class D is a digital-like amplifier that works by turning a transistor fully on or off, but the "D" technically does not stand for digital. See Class D amplifier.
Class T DIGITAL
A variation of the Class D technique from Tripath. Class T modulates the pulses based on the individual characteristics of the output transistors.
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