800 V avalanche-rugged MOSFET — the offline flyback anchor
The VIPER17HD is an offline flyback converter from STMicroelectronics' VIPer™ plus series, integrating an 800 V avalanche-rugged power MOSFET and a PWM controller in a single 16-SOIC package. It targets universal-input AC-DC power supplies up to 10 W output, where the 800 V breakdown provides adequate derating margin for 85–265 VAC rectified bus voltages, including surge transients.
115 kHz switching — transformer sizing and EMI planning
The fixed 115 kHz switching frequency sits below the 150 kHz conducted EMI test band, simplifying the input filter design compared to higher-frequency controllers. At 115 kHz, the flyback transformer can be smaller than a 60 kHz design, which helps fit the 10 W output into a compact footprint. The 70 % maximum duty cycle supports a wide input-voltage range typical of universal offline supplies.
10 W in a 16-SOIC — thermal budget is the real limit
The 10 W power rating is the practical output ceiling for this 16-SOIC (3.90 mm width) package without an exposed pad. The junction temperature range extends to 150 °C, but the designer must account for the thermal resistance of the SO-16 package — adequate copper area on the PCB and airflow are needed to keep the junction within limits at full load. The integrated 800 V MOSFET eliminates the external switch, saving board space but concentrating the heat in one device.
Protection set and supply range
Built-in fault protection covers current limiting, over-temperature, and over-voltage — the three failure modes most common in flyback converters. The Vcc supply range is 8.5 V to 23.5 V, with a 14 V start-up threshold that allows direct operation from the rectified DC bus through a startup resistor. Output isolation is supported, so the part can be used in both isolated and non-isolated topologies.