Maximum Collector Efficiency of Series-Fed Class A amplifier
Fig.1 shows a series-fed class A amplifier . This circuit is rarely used for power amplification due to its poor collector efficiency .
Fig.1: Series-fed Class A Amplifier
The d.c. load line of the circuit is shown in fig.2 .
When an ac signal is applied to the amplifier, the output current and voltage will vary about the operating point Q . In order to achieve the maximum symmetrical swing of current and voltage (to achieve maximum output power ), the Q point should be located at the centre of the dc load line.
In that case, operating point is :
IC = VCC/2RC
and VCE = VCC/2
Maximum vce (p-p) = VCC
Maximum ic (p-p) = VCC/RC
where vce and ice represents the rms value of the signals .
Thus, the maximum collector efficiency of a class A series-fed amplifier is 25% . In actual practice, the collector efficiency is far less than this value .