This reference design is a 15-W bias power supply with two isolated outputs (12 V/1.125A and 3.3 V/0.3A) and a total standby power consumption of 4 mW under a 220-V AC input. The controller uses primary-side regulation (PSR) and detects a wake-up signal from the UCC24650 secondary-side voltage-droop monitor for improved transient response to large load steps. This reference design demonstrates how the UCC28730 can provide ultra-low standby power without sacrificing start-up time or output transient response with an internal 700-V start-up switch: dynamically controlled operating states: and a tailored modulation profile. The UCC28730 uses frequency modulation: peak primary current modulation: valley switching: and valley skipping in its control algorithm to maximize efficiency over the entire operating range.