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Electronics Principles & Applications Seventh Edition

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Concept Preview

Efficiency is most important in power amplifiers.
Poor efficiency means that much of the input power is converted to heat.
A class A amplifier conducts for the entire signal cycle and has the lowest efficiency.
A class B amplifier conducts for only half of the signal cycle.
A class C amplifier conducts for less than half of the signal cycle.
A class D amplifier switches between cutoff and saturation.

Efficiency

The dc power supplied to an amplifier is PIN = VCC x IDC
Efficiency = POUT/PIN x 100%
The maximum efficiency for Class A amplifiers with a dc collector resistance and a separate load resistance is 25%.
Class A is usually not acceptable when watts of power are required.

Concept Review

Efficiency is most important in power amplifiers.
Poor efficiency means that much of the input power is converted to heat.
A class A amplifier conducts for the entire signal cycle and has the lowest efficiency.
A class B amplifier conducts for only half of the signal cycle.
A class C amplifier conducts for less than half of the signal cycle.
A class D amplifier switches between cutoff and saturation.