Television High Voltage Edge-Lit Topologies

Edge-lit configurations use external power supplies and NFETs to allow voltage power supplies to drive a larger number of LEDs (72 LEDs) per string and can sink up 1A (determined by NFET ratings). Atmel LED drivers can drive up to 16 parallel strings of LEDs and offer fault detection and management of open-circuit and short-circuit LEDs. These devices address the edge-lit and high-brightness LEDs which require higher power while enabling dimming via external pulse width modulation (PWM) signals or analog current control with an internal digital-to-analog converter (DAC).

Edge-lit topologies are the most popular backlight architectures in current LCD television applications because they are less expensive (requires fewer LEDs) compared to direct-backlight topologies. Edge-lit designs are also capable of offering zone (regional) dimming but are limited to larger tiles (coarse zones) and require expensive diffusers which use light guides to distribute light to desired zones. Edge-lit applications require an external DC-to-DC supply to boost the supply up to 250V to allow 72 LEDs per string. Television manufactures also implement LED string phase shift to reduce the overall RMS power requirements and minimize EMI noise by effectively driving one LED string at a time within a frame time period.

TopologyDescriptionAtmel LED Driver
  1. 15" to 32" Panels
  2. Global Dimming
  3. 2 Light Bars
  4. 1 to 3 Strings Per Light Bar
  5. Most Economical, Low NIT Output
  • 4 LED Strings
  • Up to 1A Per String (External FET)
  • Adaptive Power Scaling
  • ¼ Auto Phase Shift (MSL2042)
  • I2C Serial Interface
  1. 32" to 42" Panels
  2. Coarse 2-D Dimming
  3. No Scanning
  4. 4 Light Bars
  5. 2 to 3 Strings Per Light Bar
  • 8 LED Strings
  • Up to 1A Per String (External FET)
  • Adaptive Power Scaling
  • 12 Bit Phase Shift
  • Scalable
  • I2C Serial Interface
  1. 50" to 60" Panels
  2. Coarse 2D Dimming
  3. 8 to 16 Light Bars
  4. 2 to 3 Strings Per Light Bar
  5. Expensive Light Guides
  • 16 LED Strings
  • Up to 1A Per String (External FET)
  • Adaptive Power Scaling
  • 12-Bit Phase Shift
  • Scalable
  • SPI or I2C Serial Interface
LED Backlight ConfigurationProduct Number# of StringsMax String Current# of EOPower Supply Configuration
Edge-LitMSL20414DENR2External Current Sinks, External LED Supply

DENR=Determine by External NFET Ratings, EO=Efficiency Optimizer

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