Current-mode PWM controller for boost and flyback
The STMicroelectronics UC3844BD1013TR is a current-mode PWM controller designed for step-up (boost) and step-up/step-down (flyback) topologies. It drives a single external transistor and includes frequency control, with switching up to 500 kHz. The controller operates from a 10 V to 30 V supply and delivers a maximum duty cycle of 48%, which limits the off-time for transformer reset in flyback converters.
The 48% duty-cycle ceiling is the key parametric difference from the UC3842 family (which runs to 96%). In a flyback, the off-time must be long enough to reset the transformer core; 48% ensures the core resets every cycle without saturating. If your design needs more than 48% on-time, this part won't fit — you'd look at the UC3842 or a different controller. Switching up to 500 kHz lets you shrink the transformer and output filter, but the gate-drive losses and snubber design get tighter above 200 kHz. The 8-SOIC package handles the dissipation if you keep the total gate charge of the external MOSFET within the driver's capability.
Temperature grade and mounting
Not suitable for automotive under-hood or industrial extended-temp applications without a temperature-grade upgrade. Surface-mount in the 8-SOIC (3.90 mm width) package. The SOIC footprint is standard; the tape-and-reel option (TR) feeds pick-and-place lines, and the cut-tape (CT) option works for prototype or low-volume builds.