48% duty cycle — the UC3845 differentiator
Its defining parametric constraint is a maximum duty cycle of 48%, which sets it apart from the UC3842 (96% duty) and UC3843/4 (100% duty) siblings. This lower duty ceiling is intentional — it guarantees adequate reset time in single-ended forward converters and prevents transformer saturation in flyback topologies operating in continuous conduction mode.
Switching frequency and supply headroom
The oscillator runs up to 500 kHz, allowing the designer to shrink the magnetic components — transformer and output inductor — at the cost of higher switching losses. The supply range spans 7.6 V to 30 V on Vcc, which covers most off-line bias rails and industrial DC buses. No clock sync input is provided, so the switching frequency is set by a single RT/CT network; multiple converters on the same board must either free-run or use an external clock injection circuit.