What is Class AB Power Amplifier, Feedback Amplifiers, Electronic Devices & Circuits.....DISCLAIMER:Copyright Disclaimer under section 107 of the Copyrig. Therefore, maximum collector efficiency is given by, η max = (Pac / Pdc ) * 100. Substitute the value of DC power input and AC power output in the above equation, we get, η max = [ (I c2 R L ') / 2 I c2 R L ' ] * 100. η max = 50%. The above expression shows that in class A amplifier, maximum 50% of the DC power supplied can be converted.