[wind_magic]

PWM is not a great new invention designed to do anything special, it's just the way that processors create a specific voltage from a higher voltage. Computers are digital so they have to use tricks to create specific voltages. An older analog system might have complicated networks of components or transformers to create 9 volts from 12 volts for example, but computers do it with tricks. The trick is that the digital circuit switches the 12 volts on and off extremely fast. It changes the width of these pulses (thus - Pulse width modulated!) as kind of a duty cycle. So for example if the pulses were as wide as the spaces between them then that is about a 50% duty cycle, so the 12 volts will average out to be around, well, whatever, 6 volts I guess. And if the pulses are longer the voltage is higher, whereas if the spaces are longer the voltage is lower. If it's just one big pulses that never turns off, that's DC 12 volts. If it's just one big space that never turns on, that's DC 0 volts. So basically PWM is just a digital way of turning a voltage like 12 volts into any voltage from 0-12 volts without having to spend a pile of money on a bunch of complicated expensive components. It's a trick that computers use instead of using expensive digital to analog converters and things like that.

That you might get some tertiary benefit from using PWM to charge batteries is just a terrific side effect if it is true. PWM is just how basically any processor creates voltages these days. And it has downsides too, turning that voltage on and off can create frequencies that interfere with radios and all kinds of stuff, so you have to be careful when you design it. Using a more expensive circuit like a digital to analog converter and running that through an amplifier is much less noisy and accomplishes the same thing (at a greater price). Stereo systems could use PWM to create the voltages necessary to reproduce music on speakers, but it would sound like crap, that's why the more expensive digital to analog (DAC) converters are used in stereo systems and places where all that noise generated by PWM would be considered ugly and bad.