Push Pull Amplifiers ET5

Emitter Followers We have seen Emitter Followers being used with Voltage Followers to give us a good balance between Power Transfer and Voltage Transfer. Emitter Followers transfer current from one stage to another and thus have good power transfer. The problem lies in the fact that the transistor will only conduct when the AC signal is positive. Emitter Followers 0V V in V out

Push Pull Amplifiers These are designed to compensate for the single solitary arrangement of the emitter followers and will now conduct when the signal is both positive and negative. TR1 will conduct when V in is positive and TR2 will conduct when V in is negative. The two LEDs connected to V out are lit in turn when the corresponding transistor is switched on

Push Pull Amplifiers (Graph) There is a slight problem associated with the push pull amplifier arrangement. Transistors require a 0.7V difference between the base and the emitter in order for them to start conducting. As we can see from the two graphs the Output voltage does not perfectly reflect the input voltage. There is an area called cross over distortion where neither transistor is conducting due to them requiring 0.7V to switch them on. Input Voltage Output voltage

Power Amplifiers There is an equation specifically used for working out the Power dissipated from a Load connected to the output of a Power Amp