UC3861DW | Texas Instruments

Resonant-Mode Power Supply Controlle, UC3861DW, Texas Instruments

The UC3861DW is an integrated circuit optimized for the control of Zero Current Switched (ZCS) quasi-resonant converters. It features on-time–programmed one-shot pulse steering logic, making it well-suited for ZCS applications. This device is part of a broader family that offers variations in undervoltage lockout thresholds and output configurations; however, the UC3861DW specifically supports on-time control for ZCS topologies. Key control blocks within the UC3861DW include a high-performance error amplifier used to close the overall system loop, and a voltage-controlled oscillator (VCO) with programmable minimum and maximum frequencies.

The VCO triggers a one-shot that generates pulses of controlled maximum width, which can be further modulated by a Zero Detection comparator. This setup enables accurate "true" zero current switching, even under varying line, load, and temperature conditions, and accounts for tolerances in resonant components. An integrated undervoltage lockout (UVLO) feature ensures safe startup during power-up. During UVLO, the supply current is typically less than 150 µA, and both outputs are actively held low to prevent undesired switching.

Features

• Zero-Crossing Terminated One-Shot Timer
• Programmable Restart Delay Following Fault
• Low Start-Up Current