The UCC28740 isolated-flyback power-supply controller provides Constant-Voltage (CV) using an optical coupler to improve transient response to large-load steps. Constant-Current (CC) regulation is accomplished through Primary-Side Regulation (PSR) techniques. This device processes information from opto-coupled feedback and an auxiliary flyback winding for precise high-performance control of output voltage and current.
An internal 700-V startup switch, dynamically controlled operating states, and a tailored modulation profile support ultra-low standby power without sacrificing startup time or output transient response.
Control algorithms in the UCC28740 allow operating efficiencies to meet or exceed applicable standards. The drive output interfaces to a MOSFET power switch. Discontinuous conduction mode (DCM) with valley-switching reduces switching losses. Modulation of switching frequency and primary current-peak amplitude (FM and AM) keeps the conversion efficiency high across the entire load and line ranges.
The controller has a maximum switching frequency of 100 kHz and always maintains control of the peak-primary current in the transformer. Protection features keep primary and secondary component stresses in check. A minimum switching frequency of 170 Hz facilitates the achievement of less than 10-mW no-load power.
Less than 10-mW No-Load Power Capability
Opto-Coupled Feedback for CV, and Primary-Side Regulation (PSR) for CC
Enables ±1% Voltage Regulation and ±5% Current Regulation Across Line and Load
700-V Startup Switch
100-kHz Maximum Switching Frequency Enables High-Power-Density Charger Designs
Resonant-Ring Valley-Switching Operation for Highest Overall Efficiency
Frequency Dithering to Ease EMI Compliance
Clamped Gate-Drive Output for MOSFET
Overvoltage, Low-Line, and Overcurrent Protection Functions