Class D Amplifier

I have been building audio amplifiers for one of my clients for a while now but we’ve been having some overheating issues so I decided to go high-tech, ditch the old-school linear amp and use a class-D amp.

A class-D amp works a little differently from a traditional analogue amp in that it generates a high-frequency square wave which is pulse-width-modulated. This square wave is then put through a low-pass filter to knock the corners off it and you end up with a wave the same shape as the input wave. This is very clever because a transistor is most efficient when it is either fully off or fully on. By avoiding the linear analogue section of the transistor’s range, the power efficiency is very much improved.

After some research I decided to use the TPA3113 from Texas Instruments. I wired this thing up according to the recommended application circuit and it works pretty well. TI claim this device has a power efficiency of 87% and no heatsink is required. I have yet to properly load-test it but my initial tests are very promising.

The only drawback with this part is it’s sensitivity to power supply noise. A little ripple in the input voltage can make for some very nasty buzzing noises so I’m going to have to add some DC filtering.

This picture is of the whole board. The chip on the right is the class-D amp, the other chips are… well, I haven’t got it all working yet so I’ll leave that for a future blog post.

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