Solid-State Power Amplifiers
In this chapter we will examine the basic operation of some common power amplifier circuits. Recall that the capacitively coupled, class A amplifiers covered in the last chapter have a maximum theoretical efficiency of 25%. This means that if you were to design a perfect class A amplifier that delivered 10 W to a load, the amplifier itself would dissipate 30 W. Nearly all of this power would be dissipated by the output transistor(s), which would require a large heat sink. Recall also that most of the discrete transistor amplifiers examined in Chap. 3 were common emitter (CE) amplifiers. The output resistance of the CE tends to be high—typically thousands to tens of thousands of ohms. This makes the CE amplifier unsuited for driving a low resistance load, like a loudspeaker which will typically have a resistance of 8 Ω or less.