Current-mode PWM controller with topology flexibility
The UC3846J from Texas Instruments is a current-mode PWM controller designed for step-up and step-up/step-down conversion across boost, flyback, forward converter, half-bridge, and push-pull topologies. Its dual transistor-driver outputs and integrated clock sync make it a natural fit for isolated power supplies in telecom, industrial, and server applications where the 0°C to 70°C ambient range is acceptable.
500 kHz switching, 50% duty — what it means for the design
The 500 kHz switching ceiling allows smaller magnetics and reduced output capacitance, shrinking the bill of materials. The 50% max duty cycle is a hard limit — push-pull and half-bridge converters naturally fit within this window, but a boost or flyback requiring >50% on-time at low input voltage will need a different controller.
Supply range and control features
Operates from 6.95 V to 40 V on the Vcc/Vdd rail. Current limit, enable, frequency control, and soft start are on-chip. Synchronous rectification is supported.
Package and lifecycle — the sourcing reality
Housed in a 16-pin ceramic DIP (16-CDIP, 0.300" body), this is a through-hole part suited for high-reliability or legacy designs where a hermetic package is specified. The laser-etch on the top surface should show consistent font and date-code alignment with TI's plant marking — any re-marked or sanded surface is a red flag. Lifecycle status is active per the manufacturer, so no last-time-buy pressure exists for new designs. RoHS non-compliant, so verify your assembly process if lead-free requirements apply.