ZHCSBB1D July 2013 – March 2018 UCC28740
The UCC28740 is a flyback power-supply controller which provides high-performance voltage regulation using an optically coupled feedback signal from a secondary-side voltage regulator. The device provides accurate constant-current regulation using primary-side feedback. The controller operates in discontinuous-conduction mode (DCM) with valley-switching to minimize switching losses. The control law scheme combines frequency with primary peak-current amplitude modulation to provide high conversion efficiency across the load range. The control law provides a wide dynamic operating range of output power which allows the power-supply designer to easily achieve less than 30-mW standby power dissipation using a standard shunt-regulator and optocoupler. For a target of less than 10-mW standby power, careful loss-management design with a low-power regulator and high-CTR optocoupler is required.
During low-power operating conditions, the power-management features of the controller reduce the device-operating current at switching frequencies below 32 kHz. At and above this frequency, the UCC28740 includes features in the modulator to reduce the EMI peak energy of the fundamental switching frequency and harmonics. A complete low-cost and low component-count charger-solution is realized using a straight-forward design process.