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Maxim > Design Support > Technical Documents > Application Notes > Battery Management > APP 5287
Maxim > Design Support > Technical Documents > Application Notes > LED Lighting > APP 5287
Maxim > Design Support > Technical Documents > Application Notes > Power-Supply Circuits > APP 5287
Keywords: LED, low voltage, lithium, battery, single cell, high brightness, emergency lighting, LED driver
APPLICATION NOTE 5287
Simple Low-Voltage High-Brightness (HB)-LED
Solution for Li+ Battery-Operated Systems
By: Keith Welsh, Senior Member of the Technical Staff
Apr 11, 2012
Abstract:
High-brightness
(HB) LEDs are a good solution for battery backup lighting applications, most notably
emergency lighting. However, it can be a challenge to combine highly efficient LED light sources with high-
capacity, single-cell Li+ batteries. This application note presents a practical solution using the MAX16834 HB
LED driver to power a series of HB LEDs from a low-voltage source.
A similar version of this article appeared in the March 2012 issue of Electronics magazine.
Overview
High-brightness (HB) LEDs are now available for a wide range of lighting applications. The light output, often
referred to as "luminous efficacy" and measured as lumens output per watt consumed, now exceeds that of
even fluorescent lighting systems. Reliability and intrinsically safe operating voltages make HB LEDs a good
solution for battery backup lighting systems like those found in emergency lighting.
With the advances in LED devices have also come improvements in battery technology. Energy densities for
the highest capacity lithium-ion (Li+) cells now exceed ~750kJ/kg. Nickel manganese hydride (NiMH) cells have
lower energy density at around 200kJ/kg. (For comparison, note that petrol is about 44MJ/kg.) A single-cell Li+
battery has a terminal voltage of around 3.7V. Consequently, unless multiple cells are placed in series, which
introduces design challenges such as power sharing, a user will often prefer to work with a single-cell solution.
The challenge today is to marry highly-efficient LED light sources with high-capacity, single-cell Li+ batteries
where the available supply voltage is only 3V to 4V. This application note presents a practical solution using the
Maxim MAX16834 HB LED driver to power a series of HB LEDs from a low-voltage source.
Successive Boosts of the Supply and LED String Voltages Are
Inefficient
Consider the common topology of a boost configuration such as the standard MAX16834 HB LED driver
evaluation (EV) kit, the MAX16834EVKIT (Figure 1).
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