I have a test on friday. Im trying to answering this tutorial:
1. Assuming all components are ideal and that the BJTs are linear
8. How would you alter a Class B amplifier to make it into a Class A amplifier. Give full reasoning for ALL the changes you might effect. [10]
I said that you should add a bias voltage to the base of the 2 complementary BJTs in the output stage. Adjust the bias until the current flowing through a BJT=half the peak load current.
The peak load current= 2 IQ hence IQ running down on average will make a class A amplifier.
9. If the devices were now to be considered to be real devices, what would change and by how much? [10]
Uhmmm this is were im totally stumped. Somebody please lead me in the right direction....
Need a heatsink that can get rid of 5 times as much dissipated power and a transformer that can deliver 5 times as much power.
{since the PD of a class B is 5 times better than a class A amplifier}
The power handling capabilities of the bjts in a class A amplifier is hard since they have to soak up twice the output power. There is always a constant delivery of power into a class A stage even when there is no signal hence will need bigger bjts as well.
4. Given that the stage in the attached diagram is running on the limit of Class A, calculate the maximum input power and hence determine the efficiency at: