Magazine article from our research archive:

Optical feedback extends white LEDs' operating life.

Bjoy Santos, Intersil Corp, Milpitas, CA

Edited by Brad Thompson and Fran Granville

Regardless of its color, an LED's light output varies as a function of forward current and ambient temperature. As Figure 1 shows, an LED's light output can vary by as much as 150% over its operating-current range. In response, a designer's first attempt to solve the problem focuses on driving the LEDs with a constant current. The most common white-LED-driver circuits use an inductor-based dc/dc boost-converter topology similar to the circuit in Figure 2 . A current-feedback controller ensures that the voltage across current-sensing resistor R1 remains constant. As a result, the ...

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