App note: LED diagnosis in automotive applications


App note from OSRAM about different approaches on LED string diagnostic in automotive. Link here (PDF)

One requirement especially in automotive applications is the diagnosis of failures in functions and systems. Therefore light functions realized with LEDs like break light, daytime running light, low and high beam may require a diagnostics function. This application note describes some items which have to be taken into account, when a diagnostic function for a LED string or a multi LED module has to be realized.

App note: Thermal management basics and its importance for LED luminaire performance and cost


Article about thermal management on LED luminaire from TT Electronics. Link here (PDF)

LED luminaires are being marketed today as an alternative lighting technology that reduces power consumption and maintenance costs for commercial and residential installations. Thermal management has a significant impact upon the lifetime, performance and cost of an LED luminaire. Without proper application of thermal management design principles, the potential benefits of solid state lighting and its ability to be successfully marketed will be reduced.

App note: Improve flicker performance of direct AC driven LED fixtures with self valley fill


Application note from ON Semiconductors on LED lighting flicker caused by its own AC supply by adding an improved self valley fill circuit. Link here (PDF)

To provide power to LED loads from AC input, SwitchMode Power Supplies (SMPS) are generally used since LED need to be driven by regulated current. Consequently, LED lighting solution have to inherit the design complexity of a typical SMPS which includes designing the magnetic component, handling of Electromagnetic Interferences (EMI) as well as implementing Power Factor Correction (PFC). Direct-AC Drivers (DACD) for LEDs provides a new way to drive the LED load from an AC input with much simpler system architecture while satisfying EMI and power factor (PF) requirements with minimal effort. However, its drawback is flickering of light output at the zero crossing of AC line voltage due to loss of current to the LED load.

Though flicker is not always obvious, it can still cause headaches for a small percentage of people exposed to flickering lights for long periods. This is a major issue for offices, schools, stores and other brightly lit commercial and industrial spaces where people spend a lot of time.

App note: Controlling LED lighting using triacs and quadracs

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Solid State device and circuits for controlling LEDs lighting, replacing conventional incandescent lamps, an App note from Littlefuse. Link here (PDF)

Light Emitting Diodes (LEDs) are fast becoming the most popular lighting option. Industry forecasts anticipate the market will continue to expand at an annual rate of 20% from 2011 to 2016, with the greatest growth coming in the commercial and industrial lighting sectors. As incandescent lamps have been made largely obsolete, given the U.S. government’s mandate to save energy, they have frequently been replaced by LEDs due to their long life (typically 25,000 hrs.) and the ease of adapting them to many different socket and shape requirements. However, LED lighting control presents a few problems not encountered with incandescent lamps. For example, with much less current from the LED load, normal types of triacs may be challenged in terms of latching and holding current characteristics.

Triacs make up the heart of AC light dimming controls. Triacs used in dimmers have normally been characterized and specified for incandescent lamp loads, which have high current ratings for both steady-state conditions and initial high in-rush currents, as well as very high end-of-life surge current when a filament ruptures.

Because they are diodes, LEDs have much lower steady-state current than incandescent lamps, and their initial turn-on current can be much higher for a few microseconds of each half-cycle of AC line voltage. Therefore, a spike of current can be seen at the beginning of each AC half-cycle. Typically, the current spike for an AC replacement lamp is 6–8 A peak; the steady-state follow current is less than 100 mA.

Designing an AC circuit for controlling LED light output is very simple when using the new Q6008LH1LED or Q6012LH1LED Series Triacs because only a few components are required. All that is needed is a firing/triggering capacitor, a potentiometer, and a voltage breakover triggering device.