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Class "Push Pull"
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| Push Pull, is two class B amplifiers
drivers, one conduct the signal while the other driver is in off
state and vice versa, that takes advantage of the fact that speakers
loads can be driven by step up transformer. Push Pull is a good
amplifier, results in an effective increasing the voltage
swing yielding determinate by the relation of primary and
secondary turns ratio of the transformer with a single power
supply. |
| Advantages: |
| No Bias current. Since NPN output transistors alternate (On to Off) there is no sink current.
Efficiency is approximately 60%. Germanium devices are used to
reduce greatly cross-over distortion instead of silicon
semiconductors |
| Disadvantages: |
| The output devices alternate from
positive to negative, but there is no bias applied, therefore high
distortion called "Crossover distortion" is generated
(this is addressed in Class A/B by means of biasing the output
devices) |
| Conclusions and
comments: |
| Class Push Pull only applies to low cost
designs where high distortion is not objectionable and it is the
most popular design on portrait hand radios, this topology is the
most accepted in portrait hand radios due to high power can be
obtained by the output transformer windings turns ratio, with a
single power supply. |
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