Let's also assume I'm using a 4 ohm speaker.
With these parameters in mind I input 5v and 4ohms into the ohm's law calculator, and I get:
Ohm's Law Calculators and Formulas6.25W and 1.25A
Now look at the charts on page 5 of the amp's datasheet. The numbers I see there don't match up. In fact, there's two sets of numbers for different total harmonic distortions. How can this be? If I have a 5v supply and a 4 ohm impedance, how can the output, according to these graphs, be either 2.75W or 2.25W?
And why is it these values are so low compared with what ohms law seems to say the power should be for 5v flowing through 4 ohms of impedance?
To keep it simple you are comparing a DC power calculation to a AC (audio is a ac signal) power calculation. As the total supply voltage avalible is only 5vdc, the theoretical maximum audio power available where the whole peak to peak waveform can 'fit' within a 5vdc limit is: 5vpp = 2.5v peak = 1.767 volts RMS, and then audio watts would be (ExE)/R or (1.767X1.767)/4 ohms = 3.12 watts rms. As the chip's amplifier is not 100% efficient the 2.75 watt figure says it's running at 88% efficiency, not bad at all.
Lefty