Current-mode PWM controller for flyback and boost converters
The onsemi UC3843AD-F is a current-mode PWM controller designed for step-up, step-down, and step-up/step-down topologies including boost, buck, flyback, and forward converters. It drives a single external MOSFET through a transistor driver output, with the switching frequency programmable up to 500 kHz. The 96% maximum duty cycle is the key parametric for flyback and boost designs where the output voltage must be significantly higher than the input — it determines the transformer turns ratio and the minimum input voltage the converter can regulate down to. The 7.6V undervoltage lockout threshold means this controller requires a bias rail above 7.6V to start; a 5V-only system will need a separate bias supply or a different controller with a lower UVLO.
14-SOIC surface-mount package and temperature grade
Housed in a 14-SOIC (0.154" width, 3.90 mm body) surface-mount package, the UC3843AD-F is suited for automated PCB assembly.
The part is — verify the reel or tube quantity with your distributor when ordering production volumes, as the Bulk option may ship as loose parts in a bag rather than on a tape-and-reel carrier.