The LM3410 IC is a constant current LED driver useful in either boost converter or SEPIC design applications. A SEPIC (Single Ended Primary Inductance Converter) design allows the power supply’s output voltage to be set above, below or equal to its input voltage. In this application, the chip is configured as a boost-converter (i.e. the output voltage is greater than the input voltage).
The LM3410 is available in two fixed frequency variants. Using either the 525 kHz or 1.6 MHz clock version it is possible to build a very compact LED driver. The output stage can supply up to 2.8 A, allowing several high-power LEDs to be driven from a rechargeable Lithium cell or several 1.5 V batteries. The chip also features a dimmer input giving simple PWM brightness control.
The output current is defined by an external shunt resistor. To keep losses low the LM3410 uses an internal voltage reference of just 190 mV.
Power dissipation in the shunt resistor is therefore low. Using the desired value of LED current the value and power dissipation of the shunt resistor is given by:
R_Shunt = 0.19 V/I_LED
P_Shunt = 0.19 V*I_LED
A 10 µH coil (L1) will be sufficient for most applications providing it has a suitable saturation current rating. The Input and output capacitors should be 10 µF ceramic types with a low value of ESR. Many distributors including Farnell stock these components. The Diode should be a Schottky type (as in all switching regulators). The author has developed a PCB for this design; the corresponding Eagle files can be freely downloaded from www.elektor.com/090850. In summary, the most important features of the LM3410 are:
– Integrated 2.8 A MOSFET driver
– Input voltage range from 2.7 V to 5.5 V
– Capability to drive up to six series connected
LEDs (maximum output 24 V).
– Up to 88 % efficiency.
– Available is 525 kHz and 1.6 MHz versions.
– Allows both boost and SEPIC designs.
– Available in 5 pin SOT23 or 6 pin LLP outline.