04-01-2013, 04:52 PM
Complementary Symmetry Push-pull amplifier.
[attachment=46546]
THEORY:
A power amplifier is said to be Class B amplifier if the Q-point and the input signal
are selected such that the output signal is obtained only for one half cycle for a full input
cycle. The Q-point is selected on the X-axis. Hence, the transistor remains in the active
region only for the positive half of the input signal.
There are two types of Class B power amplifiers: Push Pull amplifier and complementary
symmetry amplifier. In the complementary symmetry amplifier, one n-p-n and another p-np
transistor is used. The matched pair of transistor are used in the common collector
configuration. In the positive half cycle of the input signal, the n-p-n transistor is driven into
active region and starts conducting and in negative half cycle, the p-n-p transistor is driven
into conduction. However there is a period between the crossing of the half cycles of the
input signals, for which none of the transistor is active and output, is zero
PROCEDURE:
1. Connections are given as per the circuit diagram without diodes.
2. Observe the waveforms and note the amplitude and time period of the input
signal and distorted waveforms.
3. Connections are made with diodes.
4. Observe the waveforms and note the amplitude and time period of the input
signal and output signal.
5. Draw the waveforms for the readings.
6. Calculate the maximum output power and efficiency.
Hence the nature of the output signal gets distorted and no longer remains the same
as the input. This distortion is called cross-over distortion. Due to this distortion, each
transistor conducts for less than half cycle rather than the complete half cycle. To overcome
this distortion, we add 2 diodes to provide a fixed bias and eliminate cross-over distortion.
[attachment=46546]
THEORY:
A power amplifier is said to be Class B amplifier if the Q-point and the input signal
are selected such that the output signal is obtained only for one half cycle for a full input
cycle. The Q-point is selected on the X-axis. Hence, the transistor remains in the active
region only for the positive half of the input signal.
There are two types of Class B power amplifiers: Push Pull amplifier and complementary
symmetry amplifier. In the complementary symmetry amplifier, one n-p-n and another p-np
transistor is used. The matched pair of transistor are used in the common collector
configuration. In the positive half cycle of the input signal, the n-p-n transistor is driven into
active region and starts conducting and in negative half cycle, the p-n-p transistor is driven
into conduction. However there is a period between the crossing of the half cycles of the
input signals, for which none of the transistor is active and output, is zero
PROCEDURE:
1. Connections are given as per the circuit diagram without diodes.
2. Observe the waveforms and note the amplitude and time period of the input
signal and distorted waveforms.
3. Connections are made with diodes.
4. Observe the waveforms and note the amplitude and time period of the input
signal and output signal.
5. Draw the waveforms for the readings.
6. Calculate the maximum output power and efficiency.
Hence the nature of the output signal gets distorted and no longer remains the same
as the input. This distortion is called cross-over distortion. Due to this distortion, each
transistor conducts for less than half cycle rather than the complete half cycle. To overcome
this distortion, we add 2 diodes to provide a fixed bias and eliminate cross-over distortion.