UCC28740DR

The UCC28740DR from Texas Instruments is a constant-voltage, constant-current flyback controller designed for isolated power supply applications. It combines optocoupled secondary-side regulation for precise voltage control (+/-1%) with primary-side regulation for current control (+/-5%). The internal 700V startup switch and dynamically controlled operating states support less than 10mW no-load power. Valley-switching and frequency dithering optimize efficiency and EMI performance. The SOIC-7 package enables compact charger and adapter designs.

The UCC28740DR implements a quasi-resonant flyback control scheme. The 700V startup switch charges the VDD capacitor from the rectified AC input. Once VDD reaches the run threshold, the controller begins switching the external MOSFET. Constant-voltage regulation uses an optocoupler feedback path where the FB pin current determines switching frequency and peak primary current. Constant-current regulation uses primary-side sensing through the VS pin, which monitors the auxiliary winding voltage during the flyback period. Valley-switching detects the MOSFET drain voltage resonant ring and turns on at the voltage minimum to reduce switching losses. Frequency dithering spreads the switching harmonic spectrum for easier EMI compliance.

• USB Type-C and PD charger power supplies
• Industrial limited power source AC-DC converters
• EV service equipment (Level 1 and 2 charger) power
• Set-top box and networking equipment power
• Appliance and white goods auxiliary power