- #1

zsolt2

- 20

- 2

## Homework Statement

Hi all.

I need a bit help with the following.

Estimate the power developed in the 8 Ω speaker of the circuit of FIGURE 2 for a 1 kHz sinusoidal input signal of 100 mV peak. All capacitors may be assumed to act as a short circuit at the frequency of operation.

Compare your estimate with that derived from a PSpice simulation.

(I uploaded a picture of the circuit)

## Homework Equations

Gv common emitter= Rc/Re , Gv emitter follower ~1 , power developed (Vrms^2)/R

## The Attempt at a Solution

The gain of the first stage(common emitter):

as the 47 ohm resistor is not bypassed the gain becomes 0.1x1000/47=2.127V

As the question is only wants an estimate the second stage (emitter folower) can be estimated to have a gain of 1. So the peak voltage in the speaker is ~2.127V

to get the power developped I need the rms voltage which is 1.5V

and the power is 1.5^2 /8 =0.281= 281mW

But when I look at the PSpice simulation it differs:

the voltage by the output of the first stage is ~1.5V and the voltage in the speaker is a peak ~1.4

and the power developed in it is 245mW peak and 150mW rms

Can you help me where am I wrong?

Thank you!