Design sample with 5W USB BJT flyback

In USB and isolated low power converter designs, quasi resonant and discontinuous conduction mode flyback converter topologies are a popular choice, due to their low parts count and relatively low cost. To reduce the cost even further, TI has developed a quasi-resonant/discontinuous current mode flyback controller with primary-side control. This removes the need for optocoupler and TL431 feedback circuitry reducing the cost of these low power designs even more. The control methodology uses a combination of primary peak current amplitude modulation (AM) and frequency modulation (FM) to regulate the output current and voltage please refer to data sheet for controller details. This design example is a theoretical design that shows how to use the UCC28722 in a 5W USB application. The calculations were used to design the UCC28720EVM-212 reference design. Note the UCC28722 is cost reduced version of the UC28720. To reduce the cost of the UCC28722 the internal start-up circuit was removed. This device requires a trickle charge resistor from the bulk input voltage during power up.

View the PDF document for more information.

Originally published by Texas Instruments Inc. at www.ti.com as "UCC28722/UCC28720 5W USB BJT Flyback Design Example".