TL2845D — current-mode PWM controller for isolated and non-isolated topologies
The TL2845D is a fixed-frequency current-mode PWM controller from Texas Instruments, built for step-up and step-up/step-down conversion in boost, flyback, and forward converter topologies. It drives a single transistor output at switching frequencies up to 500 kHz, with a maximum duty cycle clamped at 48%. The controller operates from a 7.6 V to 30 V supply rail and is specified over the -40°C to 85°C industrial temperature range. Housed in a 14-SOIC package, it includes frequency control and positive output configuration — no synchronous rectification, no clock sync. This is a workhorse part for off-line and DC-DC supplies where current-mode control and a hard duty-cycle limit are design requirements.
The 48% maximum duty cycle is a deliberate clamp typical of the UCx84x family. In a forward converter, this forces the use of a reset winding or active clamp to reset the transformer core within the off-time. In a flyback, it limits the volt-second product and keeps the core from saturating at high input voltage. The 500 kHz switching ceiling lets you shrink the magnetic components, but the duty clamp stays the same — plan your turns ratio and reset scheme around this hard limit.