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EE Times-India > Optoelectronics/Displays

Providing protection to LED drivers

Posted: 21 Jul 2009     Print Version  Bookmark and Share

Keywords:LED driver  LED protection  backlight display 

LEDs often serve as the light source in a backlighted display, and they usually operate from a low battery voltage such as that produced by two NiCd cells or one Li-ion cell. An IC from Maxim (MAX1698/A) can simplify these applications by boosting the battery voltage to a level suitable for LEDs. The chip also regulates LED current, and includes brightness-control circuitry for dimming the LEDs. The LED array and IC should always remain connected.

If you disconnect the LED array from the IC, the loss of LED current in RFB allows the voltage at FB (pin 6) to drop below the internal current-controller threshold, causing the device to begin increasing its output voltage. Unfortunately, the MAX1698 (like many similar devices) cannot sense the disconnected-LED condition, so its output voltage increases to a level that can destroy the external MOSFET and Schottky diode. This problem is present for any boost converter; not just LED drivers.

View the PDF document for more information.

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