Offline switcher with 800 V MOSFET — one part, three topologies
The STMicroelectronics VIPER115HSTR is an offline switching regulator from the VIPER™ family that integrates a power MOSFET with an 800 V breakdown rating and a PWM controller in a single 10-SSOP package. It handles buck, buck-boost, and flyback topologies, so a single BOM line can serve multiple offline converter designs — useful when you are kitting for several board variants off one reel.
The 12 W output power rating sets the practical design limit for a non-isolated flyback or buck in this package. Above that the junction temperature and inductor size push you to a bigger package or an external switch. The 120 kHz switching frequency is a middle ground — fast enough to shrink the magnetics compared to 65 kHz designs, but not so fast that the MOSFET switching losses dominate the thermal budget. The 80% duty cycle ceiling gives enough on-time for a buck from a 375 VDC rail down to a 12 V output without skipping cycles. Built-in fault protection — current limiting, overload, overvoltage, and short circuit — means the BOM does not need an external supervisor IC or crowbar circuit. That saves two passives and a bit of board area, which matters when you are laying out a compact 10-SSOP design. The start-up voltage is 16 V, and the Vcc range runs from 4.5 V to 30 V once the auxiliary winding takes over. That wide supply range gives flexibility for the bias winding design — you can set the auxiliary voltage anywhere in that band without an extra linear regulator.
No lab bench needed for assembly; a standard reflow profile works.