However, one of the main disadvantage of power amplifiers and especially the Class A amplifier is that their overall conversion efficiency is very low as large currents mean that a considerable amount of power is lost in the form of heat. Since we are interested in delivering maximum AC power to the load, while consuming the minimum DC power possible from the supply we are mostly concerned with the “conversion efficiency” of the amplifier. Basically a power amplifier is also a voltage amplifier the difference being that the load resistance connected to the output is relatively low, for example a loudspeaker of 4Ω or 8Ω resulting in high currents flowing through the collector of the transistor.īecause of these high load currents the output transistor(s) used for power amplifier output stages such as the 2N3055 need to have higher voltage and power ratings than the general ones used for small signal amplifiers such as the BC107. The main function of the power amplifier, which are also known as a “large signal amplifier” is to deliver power, which is the product of voltage and current to the load.
However, sometimes an amplifier is required to drive large resistive loads such as a loudspeaker or to drive a motor in a robot and for these types of applications where high switching currents are needed Power Amplifiers are required. Common Emitter (CE) amplifiers are designed to produce a large output voltage swing from a relatively small input signal voltage of only a few millivolt’s and are used mainly as “small signal amplifiers” as we saw in the previous tutorials.