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ed ro

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President

Ed Rodriguez was founder/CEO of Theta-J Corp(now the Clare division of IXYS Corp). In that role he developed the optical MOSFET solid state relay, now a global defacto standard in the telecommunications industry. He is a veteran of the power semiconductor, power supply and LED lighting technology industries.Early on, before becoming an entrepreneur, he was a product manager with Unitrode (now part of Texas Instruments.) Keynote speaker at 1986 MIT national conference on advanced power electronic technology, he has published dozens of feature articles in the leading technical trade magazines. He also has been noted in Forbes and Wall St Journal. He holds 22 patents with 8 pending, virtually all involving successfully commercialized products. In 2005 , he formed OptoThermal Technologies to focus on thermal management technologies related to high-power LED lighting.


ed ro

's contributions
  • 10.17.2013
  • Cooling high-power LEDs: The four myths about active vs. passive methods
  • Alex and Roy--- With all due respect-- this is an example of why thermal mgt issues are what they are. There's "theory" and "speculation". I see it every day on the web and with clients. Seems so simple an intuitive doesn't it? and then there is real world where one gets s few surprises and see what really works best and what doesn't... what details are actually. First Roy--- It turns out that the fan mounted blowing air PERPENDICULARLY into the fins is 50% more effective.and even 100% more !!!!! than blowing "across'" lateral) as is the common practice. Blowing INTO the fins is called "impingement cooling" and is FAR more effective because of greater turbulence with less air speed, allowing quiter operation. IBM and Intel have long used "impingement" cooling for CPU cooling , as I and others have as well, because of its remarkable effectiveness And contrary to what you might believe, the fact that air is blowing out only two sides rather than 4 sides(as in a pin pin sink), has no negative effect at all. What you see in the picture is probably the most effective practical cooler you could possibly create with air alone. If you were to actually test this, you would become a believer. Now for Alex---- This was simply a quickie photo, not an installed configuration, Naturally the fan needs to be mounted so that there can be air intake either from the sides or through a rear vent . I thought obvious but I guess not. Web site article format does not allow me to use more than "X" words, so I couldn't describe all the ins and outs of how it might be used Obviously, asshown, the fan could take in no air nor blow out any & I would have to have my head examined.
  • 10.08.2013
  • True or false: High-power LEDs don’t generate IR heat in the forward direction like a filament lamp
  • arioda-- Let me comment that in my application which started all this, I was using phosphor coated sheet made of PET. After my melting episodes I learned from vendor that the phosphor on that sheet has organic binders. Since 95% or all remote phosphor applications to date have only involved multiple, spread-out low power LEDs , the heat concentration just hasn't been there. so the issue was not apparent. But with 25,50 and 100 watt COB's, a different ballgame.For our own prototypes we are now switching to phosphor with inorganic binders and glass as the substrate--so there can be no melting.
  • 10.08.2013
  • True or false: High-power LEDs don’t generate IR heat in the forward direction like a filament lamp
  • fcasanellas----To answer your belief that all the heat “must be coming from the junction alone”. For all the devices (standard readily available products) in photo, I use A) the “safe” maximum operating power. That is lower than (B) the max power rating shown on data sheets. (A) is the level where most luminaire makers would agree probably should not be exceeded if good performance wanted.(B) is the level you “could” go to but performance would be degraded and you would be close to damage. In all cases my tests reflected operating the devices at about 25% (given in table as “power”) of the safe max operate power. In other words unit A was subjected to 25 watts, not its safe max power of 100 watts. So here’s the summary. In all cases the LED case measured less than 40C while material on or less than .060” from LED surface exceeded 100C.Junction temp Is derived from specified data sheet thermal resistance in conjunction with thermocouple measurement of LED substrate LED Power( W) Therm resistance(J-c) Junction temp A 25 0.20 45C B 13 0.6 48 C 25 0.25 46 D 15 0.8 52 E 6 1.7 50 F 10`` 0.8 48
  • 10.08.2013
  • True or false: High-power LEDs don’t generate IR heat in the forward direction like a filament lamp
  • Today, at client's facility in CT, we were testing a new active-cooled 600 watt high bay luminaire, using a circular LED array--on a circle diameter of 10 inches of 12 Bridgelux Vero arrays, each running at 50 watts. Standing in front of the sideways-positioned unit(the emission side) was like standing in front of a small electric space heater, although every layman" KNOWS that all the heat in an LED is transferred from the PN junction to the heat sink and then to air (except for that little bit of convective cooling by the metal surfaces along the way Those those of you much smarter than I have always known about all this radiated energy manifested in one degree or another as heat in the "forward" direction. It is of little consequence in units rated below 25 watts, But my client , a long established luminaire contract mfr learned quickly that at 600 watts, an acrylic "lens cover" quickly warped. With their not being EE's or physics majors they could ask " Just where would they have obtained the appropriate data?" ..... to tell them about magnitude of this heating effect ahead of time and how much of it there would be at 600 watts in the combined Vero arrays. They rightfully ask "where are the metrics on the LED data sheet or related app notes? The metrics are certainly there in spades for the "conducted" heat. Is it a fair question for them to ask how they might have known and understood the implications of this radiation heating?It should be emphasized that the radiated energy, regardless of how quantified ,shows up as a different heating effect depending on the material properties. Some bench testing makes that immediately obvious. So how does the non--EE/non physics major luminaire mechanical engineer deal with that variable?
  • 10.08.2013
  • True or false: High-power LEDs don’t generate IR heat in the forward direction like a filament lamp
  • Spolym-------Ahead of you on this one---I have measure the led surface gtemp with fast thermocoupple and fast IR sensor. If you turn off the power, the temp of the led surface drops like a rock in a few seconds. --but the temp of whatever it has heated while on DOES NOT DROP LIKE a rock. We are not worried at all here about how hot the LED surface gets but rather how hot that surface or its companion -radiated energy--causes something ELSE to get hot. Yes, you can turn it off , Yes, the thermocouple or thermometer may only be registering heat because of absorbed energy.. That is NOT the issue here.The issue is that the LED, when on. via its radiated energy, can cause potentially deleterious effects in nearby material of objects if one is unaware of the possible effects. It does not matter if that LED surface cools off in 2 seconds upon turnoff. If that radiated energy, while on, had melted or discolored a nearby acrylic lens over the LED, that item "REMAINS MELTED OR DISCOLORED" after the LED is off. The LED emitter in effect is acting somewhat like a high power radar antenna, which can cause permanent tissue thermal damage in a humans from 50 yards away, a fact known for over 60 years. As in this case, you can't really measure that "heat" directly or easily but you can quantify its effects. I realize that radiation experts can do the math and answer much of this in a few equations --but our problem here is reducing all this to simplistic terms useful to light fixture designers who have never heard of Dr. Max Planck.
  • 10.08.2013
  • True or false: High-power LEDs don’t generate IR heat in the forward direction like a filament lamp
  • To bring this all back to reason for info in the first place. It is clear this is all subject t to interpretation as to EXACT mechanisms occurring. I am not concerned that I get the mechanism (ie the theory) of what is happening) 100% right. I am also not concerned whether the equivalent heat is equal to 8% or 10% or 13 %..whatever.. of total power depending on the absorption characterisics of the material. . My point --!!!!! is that you will not find one word in the available tech literature about power LED arrays that even one percent of there energy can be manifested as heat anywhere other than in the PN junction and heat sinks. That would mean that 100% of users would assume !!!!!!!!! there is no conceivable way that a plastic sheet, with melting point of 100C. if placed on top of an LED array of junction temp 60C , could possibly melt. Well, it turns out they would be wrong,. --and that is my main point -that 99.9% of users are under a wrong impression because ALL --repeat--ALL LED makers have never specified or explained this mode of heating in any way and are extraordinarily remiss in that. So let's not debate the size of he raindrops or where they came from when all I'm trying to say is that if outsidce and you'r clothes are getting get wet , even though the LED makers say you can only get wet from jumping in the water, then maybe you should consider the possibility of a thing, everybody's been ignoring, called "rain" Heat that unexpectedly melts things..heat that supposedly exists in places where it is SAID NOT TO BE OR SPECIFIED IN ANY WAY , is very real heat of consequence, associated with 100% of power LED arrays and should be dealt with by LED makers,with metrics. in a way that is useful to users.
  • 10.08.2013
  • True or false: High-power LEDs don’t generate IR heat in the forward direction like a filament lamp
  • Your comments are right on-- But at same time, this stuff is "what I do" and shame on me if I had not anticipated everything you say. For that very reason, I made sure my very high temp observations occurred when A) i WAS RUNNING THE VARIOUS DEVICES AT LESS THAN 30-35 % OF FULL POWER --TO ELIMINATE THIS VERY QUESTION B) WAS MEASURING NOT THE HEAT SINK BUT THE SUBSTRATE TEMP ITSELF (BECAUSE I AM WELL AWARE OF THE INSIDIOUS THERMAL RESISTANCE WHICH CAN EXIST BETWEEN SUBSTRATE AND HEAT SINK BECAUSE OF LESS-THAN-PERFECT MOUNTING) and C) FAN COOLING THE HEAT SINK TO A FARE-THEE-WELL. In other words, I am 100% certain the junction temps were well below 60C and closer to 50. The junction itself is not a meaninful radiator of IR. Proof of that is evident in fact that there essentially is no meaningful heat emission in silicon power semiconductors of any type other than what is heading toward the heat sink. It is "IMPOSSIBLE" to demonstrate, for any silicon power device, that the top surface of the plastic package can ever be hotter than the junction. The heating effect in an LED is 100% the same as in any silicon power diode. So again, your comments on the possible high junction temp are good and very perceptive but simply not applicable in this case --and the IR from the PN junction--not present in any meaningful degree.
  • 10.08.2013
  • True or false: High-power LEDs don’t generate IR heat in the forward direction like a filament lamp
  • Doug--- I "think" I understand what you are saying but to be sure--- since the world of LED lighting technology is filled with misunderstandings of what is said or meant--- I think what you are saying is that the heating effects I have witnessed/measured--- in no uncertain terms--- with the high power 450nm LED array--very really heating--- is not due to any meaningful IR contribution, as was initially speculated--but rather entirely or almost entirely,absorption of that 450nm radiation, in various degrees of absorption, by the various material I put on it or very close to it (under1/4 inch). I am reaching this conclusion myself and further concluding, as one prior ,more knowledgeable responds stated, that the effect is just another variation of what happens when a one-wavelength laser melts appropriately energy absorbing metal from a distance. Can you agree with this.? By the way-- You mentioned how you have looked at high power 450 nm arrays and saw no IR. I would now tend to agree with you. The LED chip producers, who have been oblivious to these effects and have not published not one word on it , will ultimately need to have the proof provided to them "seven which ways". until they realize that as they spent 99% of their efforts over last 10 years on lumen-per-watt and packaging improvements, for sub-3-watt chips, they took their eye off the ball as they began to make high power COB arrays a couple years ago .
  • 10.08.2013
  • True or false: High-power LEDs don’t generate IR heat in the forward direction like a filament lamp
  • Captain--Thanks for your thoughtful response. What I am hoping is that individuals like yourself, whose experience or training has been heavy duty in this area--radiated energy-- (my own "academic" backgound in it is limited to my college physics eons ago and what I have "picked up" along way) In the thermal mgt and chip and power supply areas I have been into the nitty gritty (both theory and practice) and I think I know what's up. But as to how radiated light (visible or not) is absorbed and causes heat in this or that nearby material, I now need the comments of those who "really" know. I have created my own method of quantifying how much of the LED's total applied power manifests itself as measurable heat in the emitted-light direction (seems to be about 8%). But I am concluding that can vary as a function of the material's wavelength- specific absorption properties. So I then conclude I'd like to know if and how how that manifested absorption and heat might vary, with a 450nm blue 50 watt LED source when impinging on plastic... aluminum.. steel,... chocolate etc .That would close the loop for me.Can someone out there take me to school a little on this. We can do thhis off line if necessary. I consider this to be a big deal for future designeers of LED luminaires to understand and LDED chip makers have been AWOL on the subject since day one.
  • 10.08.2013
  • True or false: High-power LEDs don’t generate IR heat in the forward direction like a filament lamp
  • Thanks to all of you for your comments to date. Let me make one major point which perhaps has been not grasped here. There is no question there can be debate about what mechanisms exist in all this--- Infrared heat ?? absorption re-radiated energy-- Thousands of pages have been written,--all about the seeming fact that power LEDs create heat only in their PN junctions and that heat must be transfered to the air--via a heat sink or other cooling technique,or else the device destruction will occur. But the extraordinary fact is that all those assumptions and 99.9% of all those pages and all those talks--are incorrect. !! Why go looking for trouble when you have 20 other things to do--especialy when you don't have the expertise, time, equipment,patience or motivation. to invesigate something whose importance or value is not yet obvious to you or you company So to all of you users out there of 50 or 100 watt LED arrays I issue a challenge. Put the device on a a big fan-cooled heat sink.Power it up to 75% power but cool it so heat sink emp below 45C. After just 2-3 minutes try to touch the top of the LED with you finger---or--put a tiny drop of water on it. All the LED literaure in the world wil tell you that that nothing can fee hotter to the tought than the heat sink or the actual metallic subsrate. If the rare less than 40 C. in the first 5 minutes of the test you should be able to easily touch it and a tiny water drop "certainly" cannot boil off--Ya think? . SAfte rhtis little test , see if you think all the literature and all the conventional wisdom is correct. Terrific project for a grad student. Again--my major point is not to dissect the physics of all this but rather to point out where the industry has dropped the ball in being aware of something it is the alleged expert in.