Sepic -> sallen key lp -> PID -> pwm feedback
This circuit use PID to control the duty cycle of a SEPIC.
A fraction of the output is buffered, then uses a Sallen Key filter, then a PID controller, which is used to drive the control pin of a 555 which is running in monostable mode. The 555's output is applied to the gate of the MOSFET.
This version uses a comparator to generate the PWM rather than a 555.
