Maximum Collector Efficiency of Series-Fed Class A amplifier

Maximum Collector Efficiency of Series-Fed Class A amplifier

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Fig.1 shows a series-fed class A amplifier . This circuit is rarely used for power amplification due to its poor collector efficiency .

DRex Electronics

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Fig.1: Series-fed Class A Amplifier

The d.c. load line of the circuit is shown in fig.2 .

AC LOAD LINE OF CLASS A AMPLIFIER

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= VCC/2RC

and     VCE = VCC/2

Maximum vce (p-p) =  VCC

Maximum ic (p-p) = VCC/RC

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where  vce  and  ice  represents the rms value of the signals .

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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 .