5W USB flyback design review

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. To achieve relatively low no load input power and regulate the output voltage and output current this device uses a control methodology known as control law. This control methodology uses a combination of primary peak current amplitude modulation (AM) and frequency modulation (FM) to regulate the output current and voltage. This application report reviews the design of the 5W adapter, UCC28700EVM-068, evaluation module using the UCC28700 power supply controller. The design calculations are based on typical values. In a production design the values need to be modified for worst case conditions. Also note there is a MathCAD design tool that goes along with this application note to make the power supply design process easier using this device.

View the PDF document for more information.

Originally published by Texas Instruments Inc. at www.ti.com as "5W USB Flyback Design Review/Application Report".