Current-mode PWM controller for isolated and non-isolated supplies
The Texas Instruments UC3843ANG4 is a current-mode PWM controller designed for step-up, step-down, and step-up/step-down converter topologies including boost, buck, flyback, and forward converters. It delivers a single transistor-driver output with positive output configuration, capable of isolation through an external transformer, and includes frequency control for adjusting the switching regulator's timing. Switching frequency reaches up to 500 kHz, allowing smaller magnetic components at the cost of tighter layout and higher switching losses.
96% duty cycle — what it buys in flyback and boost designs
The 96% maximum duty cycle lets the controller maintain regulation through wide input-voltage dips without dropping pulses, a practical advantage in offline flyback converters with bulk-capacitor hold-up requirements. Supply range spans 7.6 V to 30 V, covering the bias rail from a 12 V auxiliary winding or a regulated 24 V bus without an extra linear regulator.
Through-hole 8-DIP — prototyping ease, board-density trade-off
Housed in an 8-DIP (0.300", 7.62 mm) through-hole package, the UC3843ANG4 is straightforward to hand-assemble and rework, but the 0.100-inch pitch consumes more board area than a surface-mount alternative.