Avoiding Hot Spots in LED Applications

The high efficiency of LEDs means they are being adopted for a wide range of applications, from digital signage and outdoor displays to illuminating anything from television studios to offices. If the systems are to be high quality, with consistent illumination, then the management of heat is critical.

With a pressure to reduce manufacturing costs, and the fact that many of these applications are in places where servicing the equipment can be difficult or expensive, many engineers use a single printed circuit board for both the LEDs and the electronics to drive them, which are mounted on the back. This reduces manufacturing cost, system size and makes repairs easy, as all that needs to be done is to swap out the board if a failure occurs.

The electronics on the back of the board need to drive the LEDs from a bus voltage of 12 V, 24 V or increasingly 48 V. If LED drivers are to be used, this voltage must be stepped-down to the 12 V, 5 V or 3.3 V that the drivers typically require, or a constant current must be generated to drive the bank of LEDs in a lighting application. Read our blog post about the PI354X family, which has been optimized for both tasks to learn more.

Putting the driving circuitry on the back of the board, however, presents a challenge. The power chain and drivers will dissipate heat, something that is a particular problem in LED applications. LEDs are sensitive to temperature, meaning both the wavelength and brightness of the LED will change as they heat up:  typically the wavelength increases by 0.1nm/°C-0.2nm/°C depending on the type of LED used; the light output will decrease with rising temperature.

The impact of heat depends upon the LED technology used, and the design of the LED. The output of blue LEDs might only fall a few percent with a 50⁰C rise in temperature, but the output from red LEDs can fall by 25% with only a 25⁰C temperature increase. The output of all LEDs, however, is affected by temperature.

In an application where the power chain is mounted on the back of the LED PCB, any power lost in the conversion and driving circuits will generate heat. If this is not managed correctly, it will be possible to see areas of the display or LED cluster that are less bright. For most applications this is not acceptable.

Although most LED driving applications strive for high efficiency, the need to ensure consistent brightness is often the biggest challenge for engineers developing for these applications. The PI354X family  is an ideal solution as they offer very high efficiency, significantly reducing the heat that has to be dissipated and making it much easier to achieve consistent brightness across the whole panel.

Tags: , ,

Comments are closed.

Find out more about our Cool-Power Buck Regulators subscribe to vicor newsletter Contact Us

Get Connected