The advanced PWM controller, FAN501, simplifies isolated power supply design that requires CC regulation of the output. The output current is precisely estimated with only the information in the primary side of the transformer and controlled with an internal compensation circuit, removing the output current-sensing loss and eliminating external CC control circuitry. With an extremely low operating current (250 µA), Burst Mode maximizes light-load efficiency, allowing conformance to worldwide Standby Mode efficiency guidelines. Compared with a conventional approach using external control circuit in the secondary side for CC regulation, the FAN501 can reduce total cost, component count, size, and weight; while increasing efficiency, productivity, and system reliability.