Question

The maximum efficiency of a class A series-fed amplifier is

• A. \(25%\)
• B. \(50%\)
• C. \(78.5%\)
• D. \(82.3%\)

Hint:

Remember the standard efficiencies: \[ \text{Class-A (Series-fed)} = 25% \] \[ \text{Class-A (Transformer coupled)} = 50% \] \[ \text{Class-B Push Pull} = 78.5% \]

Answer 1

The Correct Option is A

Concept: Efficiency of an amplifier is defined as \[ \eta=\frac{\text{AC output power}}{\text{DC input power}}\times100%. \] A Class-A series-fed amplifier conducts for the entire \(360^\circ\) of the input cycle. Although it provides excellent linearity and minimum distortion, its efficiency is quite low.

Step 1: Recall the maximum efficiency of Class-A amplifiers.
For a Class-A series-fed amplifier, \[ \eta_{\max}=25%. \] For a transformer-coupled Class-A amplifier, \[ \eta_{\max}=50%. \]

Step 2: Identify the amplifier type.
The question specifically mentions a \[ \text{Class-A series-fed amplifier}. \] Hence the applicable maximum efficiency is \[ 25%. \]

Step 3: Write the answer.
\[ \boxed{\eta_{\max}=25%} \] Therefore the correct option is \[ \boxed{(A)\;25%} \]