Current-mode PWM controller for isolated and non-isolated topologies
The Texas Instruments UC3843NG4 is a current-mode PWM 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 an external transistor with a single output, rated for switching frequencies up to 500 kHz and a maximum duty cycle of 97%.
Duty cycle and frequency — sizing the magnetics
The 97% maximum duty cycle gives the UC3843NG4 headroom for wide step-down ratios in buck or flyback designs without pulse-skipping at low input voltage. The 500 kHz switching ceiling lets you shrink the transformer or inductor core size compared to 100 kHz controllers, but the trade-off is higher switching losses in the external MOSFET — budget for a gate driver if the total gate charge exceeds 50 nC.
Supply rail and temperature — where it fits
The Vcc range of 12 V to 28 V covers standard 12 V and 24 V industrial buses, plus the auxiliary winding output of a flyback converter.
Through-hole PDIP — board integration
Housed in an 8-pin PDIP (0.300" width, 7.62 mm body), the UC3843NG4 is a through-hole part. It suits prototyping, low-volume production, or designs where hand-assembly is preferred.