Flyback controller with 120 kHz switching and 94 % duty cycle
The BM1050AF-GE2 from ROHM Semiconductor is an offline flyback switching controller designed for isolated power supplies. It operates at a fixed 120 kHz switching frequency with a maximum duty cycle of 94 %, which sets the transformer turns ratio and the output voltage regulation range for a given input bus. The controller requires an external power switch — the internal switch(s) field is marked No — so the MOSFET selection is a BOM decision that governs the peak current capability and the overall converter efficiency.
Supply range, fault protection, and temperature grade
The Vcc supply range of 8.5 V to 24 V covers the common bias rails from a 12 V auxiliary winding or a 24 V industrial bus. The 13.5 V start-up threshold ensures the controller begins switching once the bulk capacitor has charged above the undervoltage lockout release point. On-chip fault protection includes current limiting and over-voltage protection — the current limit cycle-by-cycle prevents transformer saturation during a shorted output, while the OVP monitors the output through the auxiliary winding and stops switching if the reflected voltage exceeds the threshold. The 24-SOP package with a 5.40 mm body width fits a standard SOIC footprint for reflow assembly.