High-Efficiency Off-Line CV and CC Flyback Controller with Primary-Side Regulation (PSR)


Product details


Control method Primary-side regulation Duty cycle (Max) (%) 99 Frequency (Max) (kHz) 85 UVLO thresholds on/off (V) 21/7.7 Features PSR, DCM Operating temperature range (C) -40 to 125 Rating Catalog open-in-new Find other Flyback controllers

Package | Pins | Size

SOT-23 (DBV) 6 5 mm² 2.9 x 1.6 open-in-new Find other Flyback controllers


  • Efficiency Performance Exceeds DoE Level VI and EU CoC V5 Tier-2 External Power Supply Standards
  • Primary-Side Regulation Eliminates Opto-Coupler and Secondary Feedback Components
  • Compatible with Synchronous Rectifier
  • Enables <30-mW No-Load Input Power
  • ±5% Output Voltage (CV) and Current (CC) Regulation
  • Enhanced Dynamic Load Response
  • Constant Current Output Under-Voltage Protection (CCUV) with Auto-Restart Response
  • Cable Compensation (300 mV at 5-V Full Load)
  • 85-kHz Maximum Switching Frequency
  • DCM Valley-Switching Operation
  • Clamped Gate-Drive Output for MOSFET
  • NTC Resistor Interface
  • Resistor or External HV Depletion-Mode FET Start-Up
  • Fault Protections: Input Low Line, Output Over-Voltage, Over-Current, and Short-Circuit
  • SOT23-6 Package
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The UCC28704 Off-line flyback controller is a highly integrated, 6-pin primary-side regulated PWM controller for designing high efficiency AC-to-DC power supplies with low standby power consumption to comply with global efficiency standards. The controller has ultra-low current consumption at start-up to enable designs with <30-mW no-load input power and save standby mode energy consumption. Intelligent primary-side sensing and control enables 5% output voltage and current control without using an opto coupler or secondary-side feedback circuits.

UCC28704 incorporates an enhanced load transient response technique which helps minimize the output capacitor, reducing the overall system size and cost. The controller also eliminates the need for loop compensation components which simplify the design and debugging process for power supply designers. The converter output voltage and current is regulated to prevent overstress conditions that may damage the load or connectors. Similarly, the CCUV shutdown feature monitors for an output under voltage fault to protect connectors from over heat or burn out from soft shorts, which greatly enhance overall system reliability. Board or component over temperature protection is facilitated with an NTC interface pin.

UCC28704 can be readily used with TI secondary-side synchronous rectifier (SR) controllers at 2-A or higher output current levels for higher conversion efficiency or more compact designs.

For all available packages, see the orderable addendum at the end of the datasheet.
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Technical documentation

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Type Title Date
* Data sheet UCC28704 High-Efficiency Off-Line CV and CC Flyback Controller with Primary-Side Regulation (PSR) datasheet (Rev. A) Feb. 17, 2016
Application note Minimize Standby Consumption for UCC287XX Family Aug. 01, 2019
Application note Selecting Electrolitic Bus Capacitor for Universal Input Jul. 17, 2018
Technical article Making a solar inverter more reliable than the sun Aug. 01, 2017
Technical article Powering the IoT Jan. 26, 2017
Application note Design UCC28704 With UCC24636 (PSR+SR) Jan. 12, 2017
Technical article Biasing an SR controller IC in USB smartphone charging applications Dec. 08, 2016
Technical article USB Type-C: charging a new world Oct. 04, 2016
Application note Troubleshooting TI PSR controllers Oct. 03, 2016
User guide Using the UCC28704EVM-724 10-W USB Adapter Jan. 26, 2016

Design & development

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

Hardware development

document-generic User guide

The UCC28704EVM-724 is a 10-W off-line isolated power supply providing 5-V output on a USB-A port. The converter output voltage and current are regulated to 5% accuracy without using an optocoupler or secondary-side feedback circuits. The EVM demonstrates a low-cost solution to comply with (...)

  • Universal AC input range (85-V to 265-V AC), 5-V/2-A isolated output
  • 5% output voltage (CV) and current (CC) accuracy with primary-side regulation (PSR)
  • 83% average efficiency and <60-mW standby power performance exceeds DoE Level VI and EU CoC V5 Tier-2 EPS standards
  • 80-mV p-p output voltage ripple at (...)

Design tools & simulation

SLUM541.ZIP (88 KB) - PSpice Model
SLUC603B.ZIP (391 KB)
SLUC605A.ZIP (1238 KB)

Reference designs

Many TI reference designs include the UCC28704 Use our reference design selection tool to review and identify designs that best match your application and parameters.

CAD/CAE symbols

Package Pins Download
SOT-23 (DBV) 6 View options

Ordering & quality

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