Product details


Topology Full-Bridge, Half-Bridge, Push-Pull Control mode Voltage Duty cycle (Max) (%) 50 Supply voltage (Max) (V) 22 UVLO thresholds on/off (V) 16.5/10.5 Features Error Amplifier, Green Mode, Light Load Efficiency, Multi-topology, Soft Start, Soft Switching Operating temperature range (C) 0 to 70 Rating Catalog Frequency (Max) (kHz) 500 Gate drive (Typ) (A) 1 open-in-new Find other PWM controllers

Package | Pins | Size

PDIP (N) 16 181 mm² 19.3 x 9.4 SOIC (DW) 16 77 mm² 10.3 x 7.5 open-in-new Find other PWM controllers


  • Controls Zero Current Switched (ZCS) or Zero Voltage Switched (ZVS) Quasi-Resonant Converters
  • Zero-Crossing Terminated One-Shot Timer
  • Precision 1%, Soft-Started 5V Reference
  • Programmable Restart Delay Following Fault
  • Voltage-Controlled Oscillator (VCO) with Programmable Minimum and Maximum Frequencies from 10kHz to 1MHz
  • Low Start-Up Current (150µA typical)
  • Dual 1 Amp Peak FET Drivers
  • UVLO Option for Off-Line or DC/DC Applications
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The UC1861-1868 family of ICs is optimized for the control of Zero Current Switched and Zero Voltage Switched quasi-resonant converters. Differences between members of this device family result from the various combinations of UVLO thresholds and output options. Additionally, the one-shot pulse steering logic is configured to program either on-time for ZCS systems (UC1865-1868), or off-time for ZVS applications (UC1861-1864).

The primary control blocks implemented include an error amplifier to compensate the overall system loop and to drive a voltage controlled oscillator (VCO), featuring programmable minimum and maximum frequencies. Triggered by the VCO, the one-shot generates pulses of a programmed maximum width, which can be modulated by the Zero Detection comparator. This circuit facilitates "true" zero current or voltage switching over various line, load, and temperature changes, and is also able to accommodate the resonant components' initial tolerances.

Under-Voltage Lockout is incorporated to facilitate safe starts upon power-up. The supply current during the under-voltage lockout period is typically less than 150µA, and the outputs are actively forced to the low state.

UVLO thresholds for the UC1861/62/65/66 are 16.5V (ON) and 10.5V (OFF), whereas the UC1863/64/67/68 thresholds are 8V (ON) and 7V (OFF). After VCC exceeds the UVLO threshold, a 5V generator is enabled which provides bias for the internal circuits and up to 10mA for external usage.

A Fault comparator serves to detect fault conditions and set a latch while forcing the output drivers low. The Soft-Ref pin serves three functions: providing soft start, restart delay, and the internal system reference.

Each device features dual 1 Amp peak totem pole output drivers for direct interface to power MOSFETS. The outputs are programmed to alternate in the UC1861/63/65/67 devices. The UC1862/64/66/68 outputs operate in unison alllowing a 2 Amp peak current.

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Technical documentation

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Type Title Date
* Data sheet Resonant-Mode Power Supply Controllers datasheet (Rev. B) Sep. 13, 2007
Application note U-122 A New Family of Integrated Circuits Controls Resonant Mode Power Sep. 05, 1999
Application note U-138 Zero Voltage Switching Resonant Power Conversion Sep. 05, 1999

Design & development

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CAD/CAE symbols

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PDIP (N) 16 View options
SOIC (DW) 16 View options

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