In order to minimize component count, stocked items in my junk box, and to improve efficiency as well as have software control of the power supply, I wanted to do away with inefficient, standalone linear regulators and instead use spare PWM pins on the microcontroller to generate voltages instead.

I have written a library which creates a simple feedback loop, where you specify the target voltage, and the microcontroller alters the PWM duty cycle to create the requested voltages.

More details are available on my blog.