LED thermal management: Is it just me or is it getting hot in here?
It’s clear that LED technology is producing the proverbial ‘paradigm shift’ in the lighting industry, partially in debt to changing regulations that seek to enable greater energy efficiency in lighting applications of course but also in other important markets such as automotive. In the lighting sector alone, according to a recent market report, the worldwide industrial and commercial LED lighting market is expected to reach US$86,087.9 million by 2019, with an annual growth rate of over 30 per cent from 2013 to 2019. And Europe is leading the way it seems, again largely thanks to governmental initiatives and regulations.
The longer-term benefits offered by LEDs for both the commercial and consumer world have been well made: less energy and heat expended, digital controllability, better durability and lifetime and therefore extended time between bulb replacements and achieving near-zero-maintenance. Cost is king, of course, but new semiconductor technologies mean increasingly energy efficient and price-competitive solutions are coming to market. However, this does not mean our work is done. Advancements in design and semiconductor process technologies have meant the availability of increasingly high power LEDs for a myriad of applications. Even though they are more efficient than the traditional alternatives, still a majority of the power supplied to LEDs turns into waste heat, so thermal issues are not going away anytime soon, and especially if they are space-constrained board-mounted devices. A key element of LED lighting design is therefore the thermal management to ensure reliable operation, better performance and extend device lifetimes.
Heatsinks are obviously the classic ‘passive’ way to deal with hotspots and other thermal issues – in conjunction with heat pipes taking heat to a remote heatsink, where dictated necessary by a design, and/or insulated metal substrate solutions – essentially boards that integrate a metal core usually comprising a copper- or aluminium-based alloy and a dielectric polymer layer with a high thermal conductivity for lower thermal resistance.
Fischer Elektronik, for example, has developed a range of heatsinks that targets LED applications (left). In addition to a number of star-type heatsinks that are suitable for all current LED types with different diameters, contours and lengths, the range include round and pin heatsinks, miniature cooling aggregates and case elements for accommodating LED-line modules. In addition, modified heatsink variants and versions specially adapted to customised LED applications can be made to meet design specifications. The LEDs are fastened using double-sided, thermally conductive adhesive, screw fastening or solderable surface coatings.
Another company is Aavid Thermalloy, which produces LED heatsinks (right) made of copper and aluminium. These low-cost and lightweight devices offer low thermal resistance and are available in various configurations and formable into different shapes to suit the application space, and even a complete housing heatsink including the socket for the LED is possible.
Figure 3: SynJet heatsinks from Nuventix (now part of Aavid Thermalloy) remove more heat with less air.
Pin Fin, Star and ModuLED heatsinks from MechaTronix have been developed for easy integration with products from the world’s leading high-power LED manufacturers. A Pin Fin aluminium heat sink has a long pins extending from its base to maximise its surface area, and hence the cooling effect. Cooling efficiency is maintained even when the LED lamp is at an angle, making these heat sinks particularly useful in spotlights where the beam angle is adjustable.
Figure 4: MechaTronix Pin Fin and Star heatsinks are both designed to maximize heat dissipation from the smaller possible heat sink form factor
2-piece MechaTronix Star heat sinks marry an extruded, star-shaped body to a solid base plate and come in a choice of base plate sizes from 50mm to 134 mm. Made from anodised aluminium, they’re available in clear and black versions, both with pre-tapped holes to accommodate popular LED fixtures. The company’s ModuLED coolers are optimised to balance conduction, convection and radiation cooling. As with Pin Fin heat sinks, the cooling performance remains almost unchanged with 50 degrees of tilt on the LED fixture. Available with baseplates from 47mm to 134mm diameter, ModuLED coolers come with a matrix of mounting holes that allow fast and easy attachment of a wide variety of LED engines, thereby minimising inventory requirements.
Figure 5: ModuLED heat sinks for directional lighting come with a matrix of mounting holes to suit a wide variety of LED engines
An alternative and highly innovative approach to thermal management, and also suitable for many different applications, is to use graphite heat sheets. This solution comes from ARX, a company very much at the forefront of developing materials for thermal management solutions. While also being a maker of thermal management products such as heatsinks and fans, these award-winning highly flexible and robust lightweight sheets are made from compressed pure graphite that are up to 1.5mm thick and can provide superior heat dissipation to metal heatsinks in the x and y plane directions, conducting heat far more effectively than traditional materials such as copper and aluminium. In addition, flexibility of the material means it can be formed to channel heat away from hotspots.
A final thermal management aid is to use fans, usually fitted inside an enclosure. The more advanced fans will deliver further efficiencies and save power by only operating when ambient temperature is above a maximum pre-set level. And while we’re on the subject of heat, it’s worth looking at a white paper that examines the thermal management of the power supplies that drive LEDs, available here from Excelsys Technologies, a leading maker of high-efficiency and low-profile power supplies for applications in the industrial, medical, lighting, communications and military sectors.
Overall, given the ever-rising capabilities, performance and power demands of LEDs, it is becoming increasingly apparent that thermal management should not be thought of as a mere postscript in the LED application design process. If you have any questions about this article or you would like assistance in choosing thermal management products for your next design, contact our regional technical specialists by clicking on the Ask an Expert button to the right of this blog.