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reference designUCC28740

Texas Instruments UCC28740

UCC28740 Constant-Voltage Constant-Current Flyback Controller Using Opto-Coupled Feedback

Overview

TopologyFlyback Converter
Input voltage85-265 V
Switching frequency0.14-106 kHz
Output 15 V / 2.1 A
IC revisionB

Description

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.

Features

  • Less than 10-mW No-Load Power Capability
  • Opto-Coupled 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

Remarks:

  • From Figure 1. UCC28740EVM-525 Schematic Inductor values L1=220uH, L2=1uH, and transformer T1=560uH is not considered.

Typical applications

  • Tablet computers
  • Standby Supply for TV and Desktop
  • Smart phones
  • White Goods
  • Cameras
  • USB-Compliant Adapters and Chargers for Consumer Electronics

More information

Products

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L(µH)
IR(A)
ISAT,10%(A)
RDC max.(Ω)
fres(MHz)
Version
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7447462221
SPECWE-TI Radial Leaded Wire Wound Inductor, 220 µH, 0.5 A
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Status Activei| Production is active. Expected lifetime: >10 years.
Product seriesWE-TI Radial Leaded Wire Wound Inductor
Inductance220 µH
Rated Current0.5 A
Saturation Current @ 10%0.57 A
DC Resistance1.2 Ω
Self Resonant Frequency4.8 MHz
VersionHeat Shrinking Tube 
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7508111111
SPECTransformer, 560 µH, –
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Status Activei| Production is active. Expected lifetime: >10 years.
Product series Transformer
Inductance560 µH
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