Boost Converter Drives 1A White LEDs

White LEDs are brighter and more powerful than ever. High-power white LEDs, because of their extreme luminous density and ultra-compact size, are replacing conventional bulbs in flashlights, headlamps, streetlights, and many automotive applications—anywhere a conventional bulb might be found. Some new white LEDs, such as Lumileds’ Luxeon series, improve on conventional bulbs in several characteristics, including greater luminescence, improved response time, and increased durability with decreased size and cost.

The challenge in using white LEDs in portable applications is powering them with the wide input voltage range that batteries present, such as 3.3V to 4.2V from a lithium-ion. LEDs require constant current to maintain constant luminosity. The battery-LED DC/DC converter must both step up and step down the source voltage to a 3.0V to 3.6V LED forward voltage range at a constant LED current such as 1A.

The LT3436EFE 800kHz boost converter in Figure 1 provides 1A driving current for the Luxeon III series white LED LXHL-PW09 from a lithium-ion battery. The Luxeon III white LED has a forward voltage range from 3.0V to 3.6V. By tying the LED from the output of the boost converter back to the input, as opposed to ground, the boost converter is capable of both stepping-up and stepping-down its input voltage to the LED. The effective output voltage of the converter is a boosted voltage of VIN plus VLED as shown in the schematic.

Figure 1. LT3436EFE boost converter drives Luxeon III 1A 3.6V white LED with 70% efficiency.

The LT1783 1.25MHz SOT-23 rail-to-rail op amp provides the current-sense capability and regulates the diode current to 1A when the LED ON switch is closed. When the switch is open, the LT3436 consumes only 6μA in shutdown.

Luxeon is a trademark of Lumileds Lighting


Keith Szolusha

Keith Szolusha

Keith Szolusha 是位于加利福尼亚州苗必达的ADI公司(前凌力尔特公司)LED驱动器应用经理。他于1997年和1998年获得马萨诸塞州剑桥麻省理工学院的电子工程学士和电子工程硕士学位,专攻技术写作。