Class A power Amplifier with Resistor load

Single Ended Class A power Amplifier with Resistor load

The below fig shows a simple series-fed class A amplifier with resistive load R_C. The transistor used here is under fixed biasing condition. As the input signal is applied, the transistor operates in active-region and hence the amplified power output appears across the load resistor. The static output characteristics along with input, output waveforms are shown in the below Pic 2.

                                                                   Pic 1  Series Fed Class A Amplifier

                                                    Pic 2 Input and Output Characteristics of a Series Fed Amplifier

For the purpose of analysis, we assume the static output characteristics to be equidistant for equal increments of the input excitation. When the applied input signal is a sinusoidal signal the base current varies sinusoidally and causes the transistor to amplify these sinusoidal variations. Thus the amplified output signals are also in the form of sine wave forms as shows in the above fig.

The power output of this circuit is

P = V_CI_C­ = I²_C R_C …………………………..   (1)

Where V_C and I_C are the rms values of output voltage and current respectively.The magnitudes of V_C and I_C may be found graphically from fig. I_M and V_M represent the peak sinusoidal output current swings respectively.