Power Amplifiers and Output Stages Flashcards
What is a Class A amplifier?
Full cycle 360° of conduction
What is a Class B amplifier?
Half cycle 180° of conduction
What is the equation for efficiency?
η = PLOAD/PSUPPLY
What is the average load for a Class A amplifier?
Where Vo is the peak voltage
What is the average supply power for a Class A amplifier?
How can we achieve the maximum efficiency for a Class A amplifier? State the efficiency value.
When Vpeak is equal to VCC. The maximum efficiency that can be achieved is 50%
Describe and explain the Class B amplifier configuration.
Two BJT’s are connected back to back, one NPN and one PNP.
The NPN transistor conducts for the positive part of the sine wave, and the PNP conducts for the negative half of the cycle.
The emitters for each BJT are connected to the load.
What is the average load power for a Class B amplifier?
The same as for class B. VO is peak output voltage (or voltage across load)
What is the method for finding the average supply for a Class B amplifier?
Since a Class B amplifier requires two BJT’s to conduct for the full cycle, we must find the average power of each BJT.
This is done by integrating sine between 0 and pi for the positive cycle and between pi and 2pi for the negative cycle.
We then multiply by the respective VCC and sum them
What is the final equation we receive for the average power supply for a Class B?
What is the equation for efficiency for a Class B amplifier?
What is the maximum (theoretical) efficiency we can achieve with a Class B amplifier?
When Vo = VCC,
η simplifies to be pi/4 which is 78.5%
How do we find the maximum power dissipated in a Class B amplifier?
Power Dissipated, PD = PS - PL
By differentiating PD with respect to the peak voltage we are able to equate the equation to zero and find the maximum/minimum points.
We then must differentiate again to find the value which is the maximum.
What is the final equation we receive for power dissipated in a class B amplifier?
