Constant converter drives white LEDs

Posted on Jun 4, 2012

Figure 1 shows the LT1618 driving a 1W, white Lumileds ( LXHL-BW02 Luxeon LED. You need no external op amps for this compact approach. The LXHL-BW02 has a forward voltage of 3.1 to 3.5V for 250 mA of current. Although the maximum dc rating of the LED is 350 mA, you can pulse it up to 500 mA for a camera flash. R4 is set for a 250-mA torch or dimming operation. The IADJ (current-adjustment) pin provides the ability to dim the LED during normal operation by varying the resistor setting or injecting a PWM signal. Access to both the positive and the negative inputs of the special internal constant-current amplifier allows you to place the sense resistor anywhere in the converter`s output or input path and provide constant output or input current.

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