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# The DC input power, heat generation and maximum thermal resistance of class A and B amplifiers are calculated, and the resulting numbers indicate that a Class A amplifier is an enormous power waster in comparison to a class B amplifier.

The DC input power, heat generation and maximum thermal resistance of class A and B amplifiers are calculated. We know that the AC output power is 200 Watts, and that the Class A and Class B amplifiers operate with the maximum theoretical efficiency. We also know that the BJT power transistor has a maximum junction temperature of 155 degrees C, if the ambient temperature is 25 degrees C. The calculated results indicate that the Class A amplifier is an enormous power waster in comparison to a class B amplifier.

#### Solution Preview

First, it can be shown that the maximum theoretical efficiency of a class A and B amplifier is 25% and 78.5%, respectively. As the efficiency equals the AC output power from the amplifier divided by DC power supplied to the amplifier, we can now determine the DC power delivered:

Class A: 200 W / 0.25 = 800 W
Class B: 200 ...

#### Solution Summary

This solution calculates the DC input power, heat generation and maximum thermal resistance of class A and B amplifiers. The resulting numbers indicate that a Class A amplifier is an enormous power waster in comparison to a class B amplifier.

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