Power amplifiers and power supplies
L. A. A. Warnes · 1994
A MPLIFIERS have already been discussed on several occasions in this work — FET amplifiers, BJT amplifiers and operational amplifiers. However, the load to be driven by these was of relatively high impedance resulting in small output power, just as well in view of their low efficiencies. High efficiencies are vital for power amplifiers, not because of the cost of the wasted power itself, but because the wasted power produces heat in the amplifier. Wasted power has to be removed causing inefficient amplifiers not only to be bulky and noisy, but also hot and expensive. Power amplifiers are divided into classes according to the duty cycle of the output transistors, that is the proportion of the time they spend in the active parts of their output characteristics. The common-emitter and common-source amplifiers seen in chapters 8 and 9 are both class-A.