Flyback controller for offline AC-DC
The BM1P061FJ-E2: The ROHM BM1P061FJ- is an offline flyback PWM controller designed for isolated AC-DC converter stages. It integrates current-limiting and over-voltage fault protection, and supports either output isolation configuration.
Switching frequency and duty cycle
Switching at a fixed 65 kHz, the BM1P061FJ- operates at a maximum duty cycle of 75%. The 65 kHz rate is a common sweet spot for flyback transformers in the 10-60 W range — high enough to keep magnetics small, low enough to avoid excessive switching losses in the external MOSFET.
Supply range and start-up behaviour
The controller's Vcc range is 8.9 V to 26 V, with a start-up threshold of 13.5 V. The 13.5 V start-up ensures the bias rail is well above the UVLO before the PWM begins switching, preventing hiccup on a slowly rising bulk capacitor.
Protection and isolation flexibility
On-chip fault protection covers current limiting and over-voltage — enough for basic offline supplies without an external supervisor. The output isolation is configurable as either isolated or non-isolated, so the same controller can serve a flyback with an optocoupler feedback path or a simpler primary-side regulated design.