IMPORTANCE OF POWER AMPLIFIERS

Power Amplifiers

Amplifier circuits form the basis of most electronic systems, many of which need to produce high power to drive some output device. Audio amplifier output power may be anything from less than 1 Watt to several hundred Watts. Radio frequency amplifiers used in transmitters can be required to produce thousands of kilowatts of output power, and DC amplifiers used in electronic control systems may also need high power outputs to drive motors or actuators of many different types. This module describes some commonly encountered classes of power output circuits and techniques used to improve performance.

The voltage amplifiers described in Amplifiers Module 1, Module 2, Module 3, & Module 4 can increase the amplitude of a signal many times but may not, on their own, be able to drive an output device such as a loudspeaker or motor.

                  

Types of Power Amplifiers

Now, the most well known types of amplifiers aren’t the ones described above, but power amplifier types. Often confused as the only categories of amplifiers, they are actually types of power amplifiers and are classified on the basis of the proportion of the input cycle during which the amplifier is giving an output. The proportion of the active input cycle is also known as conduction angle. For example, a 360 degrees conduction angle means that the device is always on, a conduction angle of 180 degrees means that the device is on only for half of each cycle. Now, the different types of power amplifiers are described below:

• Class G and H amplifiers add complexity to the signal and degrade it because of the need for switching depending on the input signal
• Class D amplifiers are models of efficiency, but with a loss of detail and fidelity
• Class B amplifiers generally introduce some crossover distortion, but move away from Class D, G, and H's extreme non-linearity.
• Class AB amplifiers may introduce some crossover distortion, but they get closer to the ideal of Class A for most of its operating regime.
• They are indeed the best compromise of performance versus cost.
• Class A amplifiers introduce no crossover distortion and are the most desirable amps to own, but they are expensive, run hot, and have to be very well-built.