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Transistor Push Pull Amplifier

This is the AQA version closing after June 2019. Visit the the version for Eduqas instead .

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AS and A2:
MOSFET
BJ Transistor
Class A Amplifier

This has not appeared in AQA exams at all often. This circuit is extremely similar to the MOSFET version so learning both is little harder than learning just one circuit.

A is an operational amplifier connected as a voltage follower with a voltage gain of ONE.
B and C are diodes. Combined with the two resistors, these BIAS the transistors to reduce cross-over distortion.
Cross-over distortion happens because small input signals (less than 0.7 V) are not sufficient to turn on either transistor.
D is an NPN bipolar transistor connected as an emitter follower with a gain of ONE.
D amplifies the positive half of the input signal.
E amplifies the negative half of the input signal.
E is a PNP bipolar transistor connected as an emitter follower with a gain of ONE.
The red line is NEGATIVE FEEDBACK. This feedback includes the power transistors. This also helps to reduce cross-over distortion.
D and E are power transistors and need to be cooled with a substantial heat-sink.

Power Transistors

BJT Power Transistors.jpg

For the Falstad Circuit Simulation, CTRL+Click Push Pull Emitter Followers
In options, check European Resistors and uncheck Conventional Current.

Alternatively view Transistor_Push_Pull_Bias_Feedback.txt.
Save or copy the text on the web page. Import the saved or copied text into the Falstad simulator.

Here is the new HTML5 Simulator Site.