Maximum Collector Efficiency of Series-Fed Class A amplifier

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 .

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 :

            I_C = V_CC/2R_C

and     V_CE = V_CC/2

Maximum v_{ce (p-p)} =  V_CC

Maximum i_{c (p-p)} = V_CC/R_C

where  v_ce  and  i_ce  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 .