PMP8930.2, Primary-Side Regulated Flyback with 85 - 265VAC Input, high output energy storage for long hold up output voltages

PMP8930.2, reference design uses UCC28710 primary-side regulated flyback controller to generate a 20V output from a universal AC input. a bulk capacitor with slow-charge-fast-discharge circuit is placed at flyback output to provide long hold up time for following step-down DC-DC stages. TPS54335 is used as controller and power stage for main 4V or 12V output. valley switching of UCC28710 allows this low-cost design to achieve a maximum load efficiency of 83%, no load losses are less than 70mW