A PWM controller has a line voltage input that allows using an input resistor for both start-up and power-limit compensation, thus saving the power consumption, easing the PCB layout, and shrinking the power supply size. In the integrated circuit, a mirrored-resistor used for the power limit compensation...http://www.google.com.au/patents/US6611439?utm_source=gb-gplus-sharePatent US6611439 - PWM controller for controlling output power limit of a power supply
