800 V breakdown, 20 W flyback — the design-fit anchor
The VIPER26HDTR is an off-line flyback switcher from ST's VIPer™ plus family, integrating a 800 V avalanche-rugged power MOSFET and controller in a single 16-SOIC package. The 20 W output power ceiling tells you the practical design space: auxiliary supplies in appliances, metering, industrial control, and IoT gateways that need an isolated rail from the rectified mains. The 800 V breakdown gives enough headroom for universal input (85–265 VAC) flyback designs without an external clamping snubber on the drain. The 115 kHz fixed switching frequency is a deliberate choice — high enough to shrink the transformer core, low enough to keep switching losses manageable in a SO-16 package. You size the flyback transformer for 115 kHz, not a range.
Protection set and supply range for the BOM
Built-in current limiting and over-temperature shutdown eliminate two external comparators or a supervisor IC. The Vcc operating range is 11.5 V to 23.5 V, with a 13 V startup threshold — the startup resistor and bulk capacitor are sized for that window. The output isolation is configurable as either — you can design a non-isolated buck or an isolated flyback by selecting the feedback winding and optocoupler. The 70% duty cycle limit is typical for flyback in continuous conduction mode; the transformer turns ratio and output voltage set the actual duty.
The base product number is VIPER26; the 'H' variant specifies the 20 W / 800 V rating tier within the VIPer™ plus family. Sourced per RFQ — confirm the BOM quantity and preferred distributor channel at quote time.