Current-mode PWM controller for single-ended topologies
The UC3845D8TR is a fixed-frequency current-mode PWM controller from TI, designed for boost, buck, buck-boost, flyback, and forward converters. It delivers a single transistor-driver output with a maximum duty cycle of 48% — the clamp prevents transformer saturation in single-ended designs. Switching frequency reaches up to 500 kHz, allowing smaller magnetic components and higher power density in the converter. The controller operates from a supply voltage of 12 V to 28 V, making it compatible with typical bias rails derived from auxiliary windings or linear regulators.
Duty-cycle clamp and frequency control
The 48% duty-cycle maximum is a hard limit — essential for flyback converters where the primary-side on-time must stay below 50% to reset the transformer core. Exceeding this risks saturation and primary-side switch failure. Frequency control is available as a control feature, allowing the oscillator timing to be set by an external resistor and capacitor. No clock-sync input is provided, so multiple converters must free-run or use external synchronization via the RT/CT pin.
Active production, 8-SOIC package
Supplied in Tape & Reel (TR) or Cut Tape (CT) options, in an 8-SOIC (0.154", 3.90 mm width) surface-mount package. The 8-SOIC footprint is widely second-sourced and easy to lay out on two-layer boards. Not suitable for extended industrial or automotive environments without thermal qualification.