06-08-2013, 12:37 PM
CLASS – B POWER AMPLIFIER
Aim:
To design and construct a Class – B (complementary symmetry) power amplifier.To
observe the output waveform with crossover Distortion and to measure the maximum power
output and to determine the efficiency.
Theory:
The figure illustrates a Class – B Power Amplifier, which employs one PNP, and one
NPN transistor and require no transformed. This type of amplifier uses complementary
symmetry. i.e., the two transistor have identical characteristics but one is PNP and the other
NPN.
Its operation can be explained by referring to the figure. When the signal voltage is
positive, T1 (the NPN transistor) conducts, while T2 (the PNP transistor) is cut off. When the
signal voltage is negative, T2 conducts while T1 is cut off.
Procedure:
1. Connect the circuit as per the diagram.
2. Set VS = 50mV(say) using the signal generator.
3. Keeping the input voltage constant, vary the frequency from 0Hz to 1MHz. In regular
steps. Note down the corresponding output voltage.
4. Plot the graph i.e., gain (dB) Vs frequency (on a semi – log graph)
Result
Thus a Class – B (complementary symmetry) power amplifier is constructed and the
output waveforms are observed and the maximum power output and efficiency is calculated.