Constant-Voltage, Constant-Current (CVCC) Flyback controller with Secondary Side Regulation (SSR)


Product details


Control method Secondary-side regulation Duty cycle (Max) (%) 99 Frequency (Max) (kHz) 100 UVLO thresholds on/off (V) 21/7.75 Features SSR, HV Start-up, DCM Operating temperature range (C) -40 to 125 Rating Catalog open-in-new Find other Flyback controllers

Package | Pins | Size

SOIC (D) 7 29 mm² 4.9 x 6 open-in-new Find other Flyback controllers


  • Less than 10-mW No-Load Power Capability
  • Optocoupled Feedback for CV, and
    Primary-Side Regulation (PSR) for CC
  • Enables ±1% Voltage Regulation and ±5% Current Regulation Across Line and Load
  • 700-V Startup Switch
  • 100-kHz Maximum Switching Frequency Enables High-Power-Density Charger Designs
  • Resonant-Ring Valley-Switching Operation for Highest Overall Efficiency
  • Frequency Dithering to Ease EMI Compliance
  • Clamped Gate-Drive Output for MOSFET
  • Overvoltage, Low-Line, and Overcurrent Protection Functions
  • SOIC-7 Package
  • Create a Custom Design Using the UCC28740 With the WEBENCH® Power Designer

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The UCC28740 isolated-flyback power-supply controller provides Constant-Voltage (CV) using an optical coupler to improve transient response to large-load steps. Constant-Current (CC) regulation is accomplished through Primary-Side Regulation (PSR) techniques. This device processes information from opto-coupled feedback and an auxiliary flyback winding for precise high-performance control of output voltage and current.

An internal 700-V startup switch, dynamically controlled operating states, and a tailored modulation profile support ultra-low standby power without sacrificing startup time or output transient response.

Control algorithms in the UCC28740 allow operating efficiencies to meet or exceed applicable standards. The drive output interfaces to a MOSFET power switch. Discontinuous conduction mode (DCM) with valley-switching reduces switching losses. Modulation of switching frequency and primary current-peak amplitude (FM and AM) keeps the conversion efficiency high across the entire load and line ranges.

The controller has a maximum switching frequency of 100 kHz and always maintains control of the peak-primary current in the transformer. Protection features keep primary and secondary component stresses in check. A minimum switching frequency of 170 Hz facilitates the achievement of less than 10-mW no-load power.

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Technical documentation

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Type Title Date
* Data sheet UCC28740 Constant-Voltage Constant-Current Flyback Controller Using Optocoupled Feedback datasheet (Rev. D) Mar. 23, 2018
Application note Practical Feedback Loop Design Considerations for Flyback Converter Using May 20, 2020
Application note Minimize Standby Consumption for UCC287XX Family Aug. 01, 2019
Technical article Choosing the right flyback controller for your design Aug. 24, 2018
Application note Selecting Electrolitic Bus Capacitor for Universal Input Jul. 17, 2018
Technical article How to minimize time to market in your USB Type-C™ and USB Power Delivery designs Mar. 26, 2018
Technical article Brush up on the latest motor design considerations for appliances Oct. 26, 2017
Technical article Powering the IoT Jan. 26, 2017
Application note Agency requirements for stand-by power consumption w/ offline and PoL converters Jan. 26, 2016
White paper Control Challenges for Low Power AC/DC Converters Oct. 02, 2015
White paper Control Challenges for Low Power AC/DC Converters (PPT) Oct. 02, 2015
User guide Using the UCC28740EVM-525 Jul. 02, 2013

Design & development

For additional terms or required resources, click any title below to view the detail page where available.

Hardware development

UCC24630 65W AC/DC Adapter
document-generic User guide

This is a high efficiency 65W AC/DC design using UCC24630 Synchronous Rectification Controller for a Universal input (85Vac to 265Vac) to 19.5V @3.33A output exceeding CoC-5 Tier2 and DOE Level VI performance requirements for external power supplies.

  • 91.49% @115V AC, 89.81% @230V AC 4-point average efficiency 
  • 83.14% @120V AC, 82.24% @230V AC 10% load efficiency
  • 59mW No load Power consumption at 230V AC
  • Fast turn-on time
  • <80mV output voltage ripple
  • AC line input UVLO protection
document-generic User guide

The UCC28740EVM-525 evaluation module is a 10W off-line discontinuous mode (DCM) flyback converter that provides constant-voltage (CV) and constant-current (CC) output regulation. It uses optical coupler feedback for tight voltage regulation and improved the transient response to large load steps (...)

  • Universal AC input, 5V/2.1A output
  • <20mW no load power
  • Avg. efficiency > 80%
  • Opto-Coupled Feedback for Constant Voltage Regulation and Fast Dynamic Response
  • Primary Side Control for Tight Constant Current Performance (± 5% Output Current Regulation)
  • Internal 700V Start-Up Switch to Start up the Supply (...)

Design tools & simulation

SLUM672A.ZIP (122 KB) - SIMPLIS Model
SLUC487B.ZIP (317 KB)

Reference designs

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CAD/CAE symbols

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SOIC (D) 7 View options

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