Flyback converter with integrated 800 V MOSFET
The VIPER26LN is a monolithic offline switcher from ST's VIPer™ plus family that integrates the PWM controller and an 800 V avalanche-rugged power MOSFET in a single 7-DIP through-hole package. It is designed for flyback converters delivering up to 20 W — think auxiliary supplies for motor drives, battery chargers, and industrial control boards where a discrete MOSFET-and-controller pair would eat board space and add BOM lines.
60 kHz switching, 70 % duty-cycle ceiling
The fixed 60 kHz switching frequency is a pragmatic choice: fast enough to keep the flyback transformer small, slow enough to avoid the snubber losses that 100 kHz+ designs wrestle with at 20 W. The 70 % maximum duty cycle gives enough on-time for universal AC input (85–265 VAC) without saturating the core — you size the primary inductance around that duty limit, not the other way around. Start-up is handled internally with a 13 V threshold, and the supply range from 11.5 V to 23.5 V covers the Vcc rail tolerance you get from an auxiliary winding without an external linear regulator.
Fault protection set — current limit and OTP
On-chip current limiting and over-temperature shutdown mean you do not need an external sense resistor or a thermistor for basic protection. The current limit is set internally; the OTP threshold is tied to the junction temperature, so the thermal pad on the PCB (the copper area under the 7-DIP body) directly affects the power level at which the part trips. Mind the dead-time on the feedback loop — the hiccup-mode restart after a fault cycles the bias supply, and the start-up resistor must be sized to recharge the Vcc cap within the hiccup period.