amplifieraudiocurrentoperational-amplifierpower supply
So I plan on using the VS1053 Codec connected to a class D Amp (2 x 2.8W channel) with two 3W 4 Ohm speakers. If I supply 5V to this setup, what would the current draw be at full use?
Codec: https://www.adafruit.com/products/1381
Amp: https://www.adafruit.com/products/1712
Speakers: https://www.adafruit.com/products/1669
At 100% efficiency, the power drawn from the battery will be exactly the same as the power output to the speaker.
Real amplifiers are never 100% efficient, but a class D amplifier can be pretty efficient. TI claims > 88% for the chip used in the amplifier you are looking at.
You should really look at the tas5630 datasheet.
Here is power wasted vs. power output. It is nearly a straight line. Notice a few watts are drawn all the time, even with zero output:
Another graph to study carefully is this one. Maybe two car batteries in series (for 24V) is not enough voltage to get your desired power output:
The power rating of a speaker indicates the maximum power it can accept without damage. A speaker of an equal or higher power rating than the amplifier is a good idea, otherwise the amplifier at maximum volume is likely to damage the speakers.
The volume will depend on the sensitivity of the speakers. Although sensitivity varies between speakers of different construction, sensitivity is not directly related to a speaker's power rating. Meaning, a 3W speaker will not necessarily sound "louder" than a 6W speaker connected to the same amplifier. There's no particular reason to look for a 3W speaker unless you are trying to cut costs.
Best Answer
According to the docs the efficiency is reasonably high, I believe 89% for 8Ω is mentioned.
If you want to be able to drive the speakers at full power continuously:
Total power [Watt] = number of channels × power per channel
P = 2 × 2.8 = 5.6 W
Supply current drawn for the speakers alone would be:
Current [Ampère] = Power [Watt] / Voltage[Volt]
I = P / V = 5.6 / 5 = 1.12 A
Accounting for efficiency, you are looking at 1.12 / 0.89 = 1.26A. This is with 8Ω load, efficiency with a 4Ω load will be worse.
The datasheet for the amp states another 5.5 mA supply current.
The datasheet for the codec lists power draw of up to 60 mA.
Total current draw would be at least 1.35A at full load.
However there are quite a few assumptions here and you really want some headroom for unforeseen things. Maybe you want to add a indicator LED? I did not account for an SD card or another microcontroller to control things. In practice you mustn't aim for a power supply that can't do at least 1.5A and I'd probably pick a 2A power supply as it is good practice to not push a power supply to its spec'd limits.