Question

A class A transformer coupled transistor power amplifier is required to deliver a power output of 10 watts. The maximum power rating of the transistor should not less than (a) 3W (b) 10W (c) 20 W
​

Answer 1

Answer:

(b)10 W

Explanation:

Given output power i.e., Pac = 10 W

Power dissipated across transistor, PQ = Pdc - Pac

Efficiency, ղ = Pac / Pdc

For a fixed Pac, the input power Pdc is minimum for maximum value of ղ.

Now, ղmax = 50% or 0.5 for class-A transformer coupled power amplifier.

Thus, minimum dissipated power across transistor,

PQ (min) = Pdc(min) - Pac = (Pac / ղmax) - Pac = (10/0.5) – 10 = 10

Thus, PQ (min) = 10 W

Transistor maximum power rating should be greater than or equal to PQ (min).

So, maximum power rating of the transistor should not be less than 10 W.