Current-mode PWM controller in 8-SOIC
The Texas Instruments UC3843DR-8 is a current-mode PWM switching controller designed for step-up, step-down, and step-up/step-down converter topologies including boost, buck, buck-boost, flyback, and forward converters. It drives a single transistor output and operates as a positive, isolation-capable controller—the standard architecture for offline flyback supplies using optocoupler feedback. Switching frequency reaches up to 500 kHz, allowing smaller magnetics than lower-frequency siblings. The 97% maximum duty cycle gives headroom for low-dropout flyback designs where the on-time dominates the period. No clock sync and no synchronous rectifier drive, so this is a conventional controller for cost-sensitive or mid-complexity power stages.
That is the commercial band — office equipment, appliance PSUs, indoor wall adapters.
8-SOIC (3.90 mm body width) surface-mount package.