What the 48% duty cycle ceiling means for your converter
The UC3845BN: Its defining parametric constraint is the 48% maximum duty cycle, which limits it to forward and flyback converters operating below the 50% mark — ruling out half-bridge and full-bridge architectures that need >50% duty on each output phase. Switching frequency runs up to 500 kHz, letting you shrink the transformer and output filter magnetics compared to 100 kHz-class controllers. The single transistor-driver output and the absence of synchronous rectification keep the bill of materials lean for sub-100 W offline supplies.
Supply range and operating temperature
The Vcc supply range spans 7.6 V to 30 V, which lets you bias the controller directly from a rectified AC rail through a dropping resistor — no separate regulated start-up supply needed.