Abstract: A control circuit includes a switch coupled to a transformer of a power converter for switching the transformer. A sampling circuit is coupled to the transformer to sample a reflected voltage of the transformer to generate a voltage signal. A switching circuit generates a switching signal to control the switch in response to the voltage signal. The minimum on time of the switching signal is changed in response to the change of an input voltage of the power converter. Because the pulse width of the reflected voltage is narrower at light load, the minimum on time of the switching signal helps the reflected voltage detection.

Abstract: A power supply system is introduced herein. The power supply system includes a power converter to supply a power source to an electronic circuit through an output cable of the power supply. A communication unit is coupled to the output cable of the power supply to develop a communication channel between the power converter and the electronic circuit in order to report the status of the power converter to the electronic circuit.

Abstract: The present invention provides a primary-side regulated PWM controller with improved load regulation. In every PWM cycle, a built-in feedback voltage samples and holds a flyback voltage from the auxiliary winding of the transformer via a sampling switch and generates a feedback voltage accordingly. A bias current sink pulls a bias current that is proportional to the feedback voltage. Via a detection resistor, the bias current will produce a voltage drop to compensate the voltage drop of an output rectifying diode as the output load changes. According to the present invention, the bias current can enable the PWM controller to regulate the output voltage very precisely without using a secondary feedback circuit.