Finding losses in the output stage of a power amplifier

[fantabulous68]

I get confused when I have to find the losses in the output stage.
I need to know how to identify losses correctly because i will use this info later in heat sink design.

Vcc = peak output voltage + minimum voltage losses in the circuit

Power dissipated=42% (Vcc^2/ 2xRL) for class B


I identified the losses in 1 diagram....is it correct?

The Vbe of a power transistor is higher than a simple transistor because as the current gain decreases then Vbe increases.

Minimum voltage losses= Vbe of power bjt Q12 + Vbe of simple bjt Q10 + Vce of Q11
=0.8 + 0.7 + 0.5
=2V



could someone identify losses ON the other diagrams in the output stage(only dealing with bjt losses)

 

[audioguru]

Each output transistor is a variable resistor in series between the supply voltage (or 0V) and the speaker.
So of course the output transistors get hot since they have a Vce across them and the speaker's current in them.
Vbe is almost nothing compared to the high Vce.