Audio Amplifier System Design

Thread Starter


Joined Jun 19, 2012
Pondering a high-level system design question here, thinking out loud.

I am designing a product that needs to deliver 3~5 Watts of audio power to an 8/4 Ohm speaker load.
The product runs from 24 VDC, the audio source is from a 3.3 V MCU via DAC or PWM.
The MCU requires 300 mW at 3.3 V supply.
Cost / physical size are the main design drivers here.

Option #1 - Use a switch mode regulator to create a +5V supply capable of delivering ~ 1 amp, with a small linear regulator to get 3.3V for the MCU.
Use a class-D amplifier to drive the speaker.
This idea seems like it would be efficient, but expensive.
a) Lowest power dissipation heatsink-less design.
b) No big Electrolytic coupling caps required.
c) Energy efficiency.
a) High BOM cost.

Option #2 - Use a tiny 3.3V switching regulator for the MCU, run a linear audio amp from the +24V
This option seems cheapest but very inefficient, heat sink problems might negate the savings?
a) Lower BOM cost
b) Simplicity?
a) Custom heat sink- hard to realize with SMD parts.
b) Poor efficiency.
c) Big DC blocking cap for half-bridge amplifier configuration.

What would you do?

EDIT- this is a high volume product concept- think chip level solutions.
Last edited:


Joined Jun 5, 2013
You could also make your own class D amplifier by using a MOSFET bridge controlled by the micro. The micro would use PWM at about 100KHz to switch the MOSFETs with the direction and duty cycle following the audio source.

But you won't get 3.5W RMS into 8 Ohms, unless you go higher than 5V. The theoretical max is:

P = V^2 / R = 5 * 0.707 / 8 = 2.5W