Tiny converter drives four white LEDs

25 September 2002 Opto-Electronics

Linear Technology's LT1937 is an 84% efficient, constant current white LED driver packaged in an SC-70 or a ThinSOT (profile under 1 mm). 1,2 MHz switching frequency enables extremely small externals, namely a 22 µH inductor and 0,22 µF output capacitor. The LT1937 has been optimised to drive up to four white LEDs on 3,2 V supply (6 LEDs from 5 V supply). Efficiency and <1 mA shutdown current provide optimal battery time, while input voltage range 2,5 V to 5,5 V makes it ideal for use in single cell Li-Ion and multicell Alk/NiMH battery devices. 1,2 MHz constant switching architecture minimises both input and output noise. The device delivers constant current to series-connected LEDs, ensuring uniform brightness. High accuracy feedback voltage (95 mV+ 9 mV) contributes to high efficiency and provides good brightness control even when partially dimmed to current levels of 6-8 mA.

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