What this offline flyback switch does in a power supply
The STMicroelectronics VIPER27HDTR is a monolithic offline flyback switching regulator from the VIPer™ plus family, integrating an 800 V avalanche-rugged power MOSFET and PWM controller in a single 16-SOIC package. It delivers up to 20 W of isolated output power at a fixed 115 kHz switching frequency, with an 80% maximum duty cycle. The built-in startup circuit reduces external component count, and the 8.5 V to 23.5 V supply range allows it to operate directly from the rectified mains or a bias winding. Fault protection includes current limiting, over-temperature shutdown, and over-voltage protection, making it suited for robust power supplies in industrial, consumer, and auxiliary bias applications.
20 W output and 800 V breakdown — sizing the supply
The 20 W power rating is the continuous output capability in a typical flyback topology with adequate transformer design and thermal management. At 115 kHz switching, the transformer can be smaller than a 60 kHz design, but the higher frequency increases core losses and makes layout critical to keep EMI under control.