High-efficiency flyback controller with optocoupler feedback

The UCC28742 off-line flyback controller, from Texas Instruments, is a highly integrated, six-pin secondary-side regulated PWM controller for efficient AC-to-DC power supplies. It is an isolated-flyback power-supply controller that gives Constant-Voltage employing an optical coupler to enhance transient response to large-load steps. This device processes information from optocoupled feedback and an auxiliary flyback winding for high-performance control of output voltage and current. The device uses advanced control algorithms to deliver high operating efficiency and performance. The drive output interfaces to a MOSFET power switch. DCM with valley-switching decreases switching losses. Modulation of switching frequency and primary current-peak amplitude (FM and AM) retains the conversion efficiency high across the complete load and line ranges. The controller has a maximum switching frequency of 80kHz and always keeps control of the peak-primary current in the transformer. A minimum switching frequency of 200Hz promotes the attainment of low no-load input power.