The result is that both halves of the output waveform now swings from zero to twice the quiescent current thereby reducing dissipation. Here, the load current is shared between the two power transistor devices as it decreases in one device and increases in the other throughout the signal cycle reducing the output voltage and current to zero. The transistors used for this type of transformer push-pull amplifier circuit are both NPN transistors with their emitter terminals connected together. Another center-tapped transformer on the output is used to recombined the two signals providing the increased power to the load. The circuit above shows a standard Class B Amplifier circuit that uses a balanced center-tapped input transformer, which splits the incoming waveform signal into two equal halves and which are 180 o out of phase with each other. Class B Push-pull Transformer Amplifier Circuit This pushing and pulling effect of the alternating half cycles by the transistors gives this type of circuit its amusing “push-pull” name, but are more generally known as the Class B Amplifier as shown below. Then the conduction angle for this type of amplifier circuit is only 180 o or 50% of the input signal. This results in one transistor only amplifying one half or 180 o of the input waveform cycle while the other transistor amplifies the other half or remaining 180 o of the input waveform cycle with the resulting “two-halves” being put back together again at the output terminal. Push-pull amplifiers use two “complementary” or matching transistors, one being an NPN-type and the other being a PNP-type with both power transistors receiving the same input signal together that is equal in magnitude, but in opposite phase to each other.
This creates what is commonly termed as a Class B Amplifier, also known as a push-pull amplifier configuration.
#POWER DISSIPATION BJT TRANSISTOR FULL#
To improve the full power efficiency of the previous Class A amplifier by reducing the wasted power in the form of heat, it is possible to design the power amplifier circuit with two transistors in its output stage.
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