The evaluation module is a 10W off-line discontinuous mode (DCM) flyback converter that provides constant-voltage (CV) and constant-current (CC) output regulation. It uses optical coupler feedback for tight voltage regulation and improved the transient response to large load steps and primary side control for accurate constant current regulation. The UCC28740 controller uses frequency modulation, peak primary current modulation, valley switching and valley skipping in its control algorithm in order to maximize efficiency over the entire operating range.
This evaluation module uses the UCC28740 Constant-Voltage, Constant-Current Flyback Controller Using Opto-Coupled Feed-Back in a 10 W converter to provide 2 A of constant charge current. The input accepts a voltge range of 85 VAC to 265 VAC. The output is designed for 5 V when in constant voltage mode and will deliver 2.1 A of constant charge down to an output voltage of less than 2 V. Depending upon the operating conditions, the control law algorithm will modulate the switching frequency or the peak primary current to satisfy the power transfer requirements.
As the load is increased from zero, the converter will transition through a frequency modulation mode where the peak primary current is held constant at one-quarter of its full-load peak value as the switching frequency increases from a minimum value to maintain energy transfer up to 32 kHz. When the load is increased to the level at which the switching frequency reaches 32 kHz, the controller will keep the switching frequency fix ed and modulate the peak primary current, increasing it from one-quarter its peak value up to its maximum full load peak current value; this area of operation is refered to as the amplitude modulation range.
Further increase in load demand will transition the controller into another frequency modulation mode where the peak primary current is constant at its maximum designed value and the switching frequency is increased as needed, up to the controller’s maximum 100 kHz switching frequency. Opto-coupled feed-back maintains a tightly regulated output with fast dynamic response to load transients. The controller will further enhance its efficient operation with valley switching. The UCC28740 also uses dithering of the gate drive helps to ease EMI compliance.
- USB-Compliant Adapters and Chargers for Consum er Electronics such as smart phones, tablet computers, and cameras
- Stand-by Supply for TV and Desktop
- White Good
- AC Input Range 85 VAC to 265 VAC
- DC Output of 5 V, 2.1 A
- No-Load Power Consumption less than 20 mW
- Opto-Coupled Feedback for Constant Voltage Regulation and Fast Dynamic Response
- Primary Side Control for Tight Constant Current Performance
- ± 3% Output Volage Regulation
- ± 5% Output Current Regulation
- Average Efficiency > 80%
- Output Over Current and Short Circuit Protection
- Output Over Voltage Protection
- Input Brown-Out Protection
- Auto Re-Start on Fault
- Quasi-Resonant Valley Switching
- Frequency Dither
- Internal 700V Start-Up Switch to Start up the Supply Directly From the Bulk Rail
- Evaluation Board