Ok, thanks maybe i will just try making a normal one ubt.. can it be programmed?
The short answers is yes and unless your a electronic's wizard and have the parts laying around and a few hours to debug it i would almost get a deticated IC for this or a prebuild board or kit. but far be it for me to tell you what todo.
you'll need to also google SG3526 and consider that an option
basically what your wanting to do here is...
set one of your two 555's built into the 556 is in astable operation, the other one is in monostable. the astable sets the frequency of the pwm, the mono the % of the pulse that is on. you're going to use that pulse to turn a Power MOSFET on and off.
you'll only need a pot on R1 for the monostable (you're adjusting the time the pulse is on, not the frequency)
here's where to start.