Class D Amplifier (WIP)

Fall 2017
Circuit design, testing, debugging
Passion project

This project gave me the opportunity to explore some of the aspects of audio circuits and to gain experience debugging with an oscilloscope.

Overall Goals

As a music lover, I thought it would be fun to make an amplifier. When researching the different types, Class D interested me because it combines analog and digital circuitry and would also give me an opportunity to learn about signals.

You can find the schematic capture files, pcb layout files, and Gerber files here.

Schematic

I based my schematic off a few reference schematics, as it was my first time working with an audio circuit. Since all Class D amplifiers have the same stages of processing, most of the design was choosing compatible components and component values (resistors, capacitors).

Prototyping

Before creating a PCB, I prototyped the amplifier on a breadboard to determine if any tweaks had to be made beforehand. The first time I prototyped my design, I did not use a MOSFET driver for the power switching stage of the circuit. Instead, I used a half-bridge configuration. As such, there was no dead time, when the MOSFETs were on at the same time it was a short circuit and the second MOSFET was overheating.

I added a MOSFET driver to the circuitry, which required an inverter for the high- and low- side inputs of the driver. When I prototyped the amplifier, it did not play more than static.

Debugging

As with most electronics projects, it did not work the first time. As such, I debugged it on an oscilloscope.

I found that my audio in signal and my triangle waveform was outputting correctly, but my comparator wasn't outputting a signal. I believe it is because I use GND for the low power rail instead of a -5V. My plan is to create a negative voltage generator circuit and continue testing.

PCB Design

Once I was satisfied that my amplifier would work (via online simulation, not from breadboard prototyping —yet), I created a PCB layout, ensuring that like-stages were near each other to mitigate distortion of sound.

Takeaways

Overall, this project is giving me the chance to independently explore the circuit design and debugging process. This project is a WIP, so I will continue to update as I make progress.