# Internal impedance of Class AB amplifier

amplifierefficiencyimpedance

This was a challenge problem that my instructor gave. Here is what a class AB amplifier looks like: I've looked everywhere to find out about internal impedance but I got nothing. This is the problem I'm trying to solve:

Determine the maximum peak to peak signal that can be applied to a amplifier and the efficiency rating or nstage for the amp. Assume the amp is driven by a sine source and has an internal impedance of 600 ohms.

Given:

• $$\\text{hfe} = \text{hFE} = 100\$$
• $$\V_{be} = 0.7\$$
• $$\E_s = 32.093~V_{p-p}\$$ at 1 kHz
• $$\R_L = 8~\Omega\$$
• $$\R_1 = R_2 = 1~k\Omega\$$

I've tried all that I've been taught so far. I took the internal impedance as $$\Z_{input}\$$. Then, I used $$\Z_{input}\$$ and $$\E_s\$$ to find $$\V_{in}\$$, since $$\V_{in} = V_{out}\$$ is the voltage at the load. Finally, I used that answer to find the efficiency as $$\P_L / P_{dc} \cdot 100 \$$.

I calculated an efficiency over 200%, which must be wrong. What am I doing wrong?