What the UC1861J is and where it fits
The UC1861J is a current-mode PWM controller from Unitrode (now Texas Instruments) designed for isolated and non-isolated DC-DC converters. It supports boost, flyback, forward, half-bridge, full-bridge, and push-pull topologies — a flexible part for a single-ended or dual-ended power stage. Two outputs drive external transistors with a fixed 50% maximum duty cycle, and the 50 kHz to 500 kHz switching range suits traditional ferrite magnetics. The 16-pin ceramic DIP (CDIP) package and -55°C to 125°C operating temperature range target military, aerospace, and downhole applications where hermetic sealing and extended temperature are mandatory.
Package and mounting — ceramic DIP matters
The UC1861J comes in a 16-lead ceramic DIP (CDIP-16, 0.300" body width, 7.62 mm pitch). Through-hole mounting is the only option — no surface-mount variant exists for this order code. The ceramic package provides a hermetic seal and better thermal cycling endurance than plastic DIP, which is why it shows up in avionics and satellite power supplies.
Temperature grade and environment
Rated for -55°C to 125°C ambient. The 22 V supply rail is the maximum Vcc.
Sourcing and lifecycle
It is RoHS non-compliant (leaded solder finish), so verify your BOM's RoHS exemption or accept the non-compliant status for military/hermetic programs where lead-bearing finish is often required.