Current-mode PWM controller for isolated and non-isolated topologies
The UC3843AD8G4 is a current-mode PWM controller from Texas Instruments, designed for step-up, step-down, and step-up/step-down converter topologies including boost, buck, flyback, and forward converters. Its single transistor-driver output drives an external power switch, keeping the power stage off-chip and flexible for different power levels. The part operates from a 7.6V to 30V supply rail and switches at frequencies up to 500 kHz, which lets the designer shrink the magnetics and output filter relative to lower-frequency controllers.
A maximum duty cycle of 96% means the controller can keep the switch on for nearly the whole period, which is critical in boost converters that need a high step-up ratio and in flyback converters that must hold the primary current long enough to deliver energy at low input voltage. The 96% ceiling also gives headroom for transient response without hitting the duty-cycle clamp.
Switching frequency up to 500 kHz — magnetics and EMI trade-off
The oscillator is set by an external RT/CT network, and the controller can run up to 500 kHz. At that frequency the transformer and output inductor shrink significantly, but the switching losses in the external MOSFET and the core losses in the magnetics increase. The designer balances frequency against efficiency; many production designs run in the 100–250 kHz range to keep the thermal budget manageable.
That means it is still a standard production item, not subject to a last-time-buy notice.
This part is intended for benchtop power supplies, office equipment, appliance control boards, and other indoor electronics.