Simply adding a diode and potentiometer to a 555 timer operating in the asynchronous mode yields a pulsewidth modulator ... Wide-Range Pulse-Width Modulator Uses 555 Timer. Sept. 15, 2005.

Beyond the basics, the 555 can be used for timing sequence generators, pulse position modulation, time delays, ramp generators with the addition of a current source, and a multitude of other ...

For pulse density modulation if X is too big – say, if you have a minimum time increment of 1 microsecond, and your period is 256 microseconds, and X is greater than 128 – the line idles ...

Most switch-mode power supplies rely on a PWM (pulse-width-modulated) output that is controlled via voltage feedback. A 555-timer IC can inexpensively perform PWM. The circuit in Figure 1 shows how to ...