48% duty-cycle ceiling sets the flyback transformer turns ratio
The TL3844BDR-8 is a current-mode PWM controller from Texas Instruments, built for boost, flyback, and forward topologies. Its 48% maximum duty cycle is the hard limit that governs the transformer turns ratio in a flyback — push past that and the core resets incompletely, saturating on the next cycle. The single transistor-driver output drives an external MOSFET or IGBT directly, with no internal switch. Switching frequency runs up to 500 kHz, which lets the magnetics shrink — a 200 kHz design needs roughly 2.5× the core cross-section of a 500 kHz one for the same throughput. The 10 V to 30 V supply range covers the standard bias rails from a 12 V auxiliary winding or a 24 V industrial bus.
No clock sync, no synchronous rectifier — keep it simple
The TL3844BDR-8 omits clock synchronisation and synchronous rectifier drive. That means the switching frequency is set by a single RT/CT network, and the output stage drives a diode rectifier — simpler BOM, lower parts count, but the rectifier losses are higher than a synchronous FET at low output voltages. That is fine for indoor power supplies, adapters, and telecom rectifiers, but not for an engine-bay or outdoor enclosure without active cooling.