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Sydney Evans | August 2011

2011 coolingZONE Summit Preview: Interview with Norbert Engelberts


norbert engelberts, director of advanced thermal solutions europe, will be presenting at the 11th coolingzone international business and technology summit, october 5-6, 2011 in cambridge, ma. norbert previously headed the thermal design and environmental testing group for bell labs lucent technologies (now alcatel-lucent). he has an extensive experience in the thermal management of led based lighting solutions for a variety of applications, including automotive, street lighting, led replacement lamps.

“thermal design and management of high power leds” will explain what options currently exist for cooling leds and why thermal management is important for the design of lamps based on leds. through specific case studies, engelberts will show how the right engineering design creates a more efficient product at a lower cost.  

we had the chance to sit down with norbert and ask him a few questions about led cooling solutions, why it is so important, and what he hopes attendees will take away from his presentation.

coolingzone:  how did you become interested in this problem of thermally managing led as an engineer?

norbert:  the market was requesting help and we ended up doing some consulting with led distributors and led oem’s.  so the question on “how to cool” led really bubbled up from the market.  the led providers in the market eventually realized they had a problem.  led’s are comparable to semiconductors in that they run hot.   my practical and research expertise as an engineer in thermal management of semiconductors and systems was readily applicable to the led space.

also, here in europe, there was a real push to use high power led’s since they provided similar light output for less power consumption. still, the thermal management challenges to make those lights commercially viable were real.

coolingzone:  was europe’s adoption of led driven partially by the move to consume less power in lighting?

norbert: yes that’s true.  another important motivator was a rule from the eu that consumers could no longer purchase 75 w or 100 w incandescent light bulbs.  retailers were prohibited from selling them.

coolingzone:  this brings me to an interesting question, you noted how led’s are thermally and electrically like a semiconductor.  given the move from incandescent lighting to led lighting, do engineers and lighting professionals still have their minds wrapped around incandescents vs. led?  if so, does that mean that some solutions to cooling led come from the wrong “direction” to try and frame and solve the thermal problem?

norbert:  yes that is happening, though over the past ten years we are seeing far less of this kind of design approach.  early led lighting designs were not very effective.  the designs either didn’t work at all once a product was shipping or the product only worked for a few thousand hours then failed.  so there was a good deal of trial and error until a solution worked best.   also, the led suppliers are also starting to put more effort and education into the thermal management of led.  the education is usually focused on explaining to the oem community that there are thermal issues at all and that it can’t be ignored.

now remember, one key difference driving thermal management of led lighting is the temperatures that the lights need to operate at in order to produce white light.  an incandescent bulb’s main lighting element is the filament.  a filament in an incandescent light acts as a resistor.  electrical power to the filament gets extremely hot, at least 2000 degrees c or greater.  the thermal radiation from the filament includes significant amounts of visible light.[j1]  led on the other hand is a semiconductor and the maximum temperature it has to run at is around 200 to 250 degree c  although the amount of power is much less, the thermal requirements are much more stringent.

coolingzone: your talk is going to focus on “the required approach” to developing a thermal management solution.  is there only one way or a best way to approach the problem of thermal management in led?  or is it best to take trial and error?

norbert:  you have to look from three perspectives to insure you have the right approach.  first, look at the problem from an analytical model.  second, do some cfd and get a computational read on your solution.  third, perform experiments with your proposed solution.    with these three methods you can create good thermal designs, and you come up with thermal designs that are correct the first time.   the best approach is not this, “try this or that” and see what happens. 

coolingzone:  seem like this three part methodology would lead to a faster result as well would it not?

norbert:  right.  and you know from the first time you are doing right because all the variables that can differ you can include in your solution methods so you can consider which is superior.

cooolingzone:  norbert you note in your talk that you will be focusing on junction temperature vs. total power dissipation.  is this a classic problem prevalent in many thermal management designs?
norbert:  junction temperature is key. and while focusing on the junction temperature of the led is important, a thermal engineer cannot forget about the junction temperature of the led driver.   if you have an led light,  you have a driver as well.  the driver junction temperature can often be more critical than that of the led.

coolingzone:  given the wide array of applications for led lighting, are commercial off the shelf led heat sinks useful or do most led lighting applications require a customized approach?

norbert:  to some extent, an off the shelf solution can be helpful, at least to start your design. but in most cases a custom approach has to be used.  for example, if a light fixture is part of an led light design, then the fixture itself might form part of the cooling solution.  certainly an off the shelf solution would never work.

coolingzone:  that brings me another question around what pcb type to use.  can fr4 still be used, given its limitations in thermal management or should mcpb’s be the default option?

norbert:  the reason why metal core solutions are used is to help with applications that have a fixed light source that is truly concentrated and the heat needs to be spread. the best way to do that is through a local solution, so, a design based on mcpb is a good choice.   fr4 is still being used in led lighting applications but you need to carefully design it.  you need to make use of thermal via’s.   the power of led’s is increasing. we started with 1w and now we are pushing 50w on led and in those applications you need to carefully consider the design. 

coolingzone:  norbert, as we wrap up our conversation here, what is the key message you hope attendees to your talk at coolingzone 2011 take away from your talk?

norbert:  that thermal management is important to make a successful led design, that you have to build thermal management into your design from the first architecture discussions, and there are tools that will help you come up with the right thermal management solution.

to attend norbert’s presentation, “thermal design and management of high power leds”, at the coolingzone summit, please register at https://www.coolingzone.com or email [email protected]


 [j1]source: http://www.megavolt.co.il/tips_and_info/lightbulb.html

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