LED Automotive indicator selection and construction help - Page 1
Forum section: electronics / projects

author: agilly1989
author_rank: Contributor
timestamp: November 29, 2013, 04:22:30 am
content: Hello allI'm currently in a little bit of a pickle and need a little help. I have been tasked by my Uncle and my Dad to design some replacement LED indicators for their vintage car. The main problem I think I have is the lack of skills in LED light driving.The car is an old 1920s (?) Essex that has a 6v electrical system. So I'm thinking of using a cheap LM317 as a CC source powering 2 x 39lm LEDs (Cree XLamp ML-E MLEAWT-A1-R250-0002E7http://au.element14.com/cree/mleawt-a1-r250-0002e7/high-brightness-led-warm-white/dp/1855586) in parallel.Now the questions I have for the forum are:1. Would these LED's be adequate for an indicator lamp?2. Does the LM317 CC source follow voltage? as example, I might design this for a 6v system, but what design aspects would come into play if he decides to upgrade to a 12v system?

author: mariush
author_rank: Super Contributor
timestamp: November 29, 2013, 05:08:57 am
content: Just use a proper led driver, like this one for example:http://uk.farnell.com/micrel-semiconductor/mic2287cyd5-tr/pwm-wled-driver-1-2mhz-sot23-5/dp/1663103RL2.5-10v input , up to 500mA output current ... just put two white leds in series and this controller will have no problems doing 150mA or whatever current you want to set. Read the datasheet, it's easy...or if you want cheaper (less external parts), one bcr320u/bcr321u for each led (or put the two leds in parallel)... these parts can do up to 250mA :http://uk.farnell.com/infineon/bcr321u/ic-led-driver-0-5w-leds-6sc74/dp/1791066RLhttp://uk.farnell.com/infineon/bcr320u/ic-led-driver-0-5w-leds-6sc74/dp/1791065RL

author: agilly1989
author_rank: Contributor
timestamp: November 29, 2013, 05:14:11 am
content: Thanks mariushSo I should find a LED driver for the 12v or so (if he was to upgrade) and since the LEDs are 4 pole (2 leds in 1 package) should I run all of the leds in series (like configure the LED for series and then put them both in series OR should I put the LED in parallel mode and then run them in series?

author: mariush
author_rank: Super Contributor
timestamp: November 29, 2013, 05:52:11 am
content: I didn't check the datasheet for those leds, I just looked at the description on the page and noticed forward voltage = 3.2v and current = 150mA.If you want to make everything compatible with 12v, the first chip (mic2287) is out. That chip is designed to use a low voltage (2.5-10v with an absolute maximum of 12v which won't work for you, because a 12v car battery may give you up to 14v and would damage the chip).The chip would then boost the voltage as much as needed until the current going through the led(s) on the output reaches the amount you set. The idea would be to configure the chip to 150mA, you would set two leds with 3.2v in series on the output (so you'd have a 6.4v 150mA led) and then the chip would boost the 6v input voltage to 6.4v and light up the leds.This chip only works in boost mode, so it's not easy to use such chip to light up just a couple of leds that don't need so much voltage.The other two chips (bcr320/321) are however designed differently... you power the leds directly from the input voltage and after the leds you put this chip and the chip will only let a particular amount of current to the ground.So with such chip, it doesn't matter if the input voltage is 6v or 12v (the chip supports up to 25v input voltage), you just put one or more leds in series and then after the leds you put this chip and configure it to only let 150mA (or whatever value you want) go through.Naturally, with this chip, the input voltage must be higher than the voltage dropped on the leds and the chip itself ... so you can't use a 6v input voltage and put two leds in series (as these would need 6.4v to light up).The led you linked has the leds connected in parallel , so you have a forward voltage of 3.2v and max current of 150mA ... so in the picture above you just have to have the input voltage higher than 3.2v and the resistor near the chip to about 5-6 ohm (which gives you 150mA):Note that there's some other gotchas you can deduct from the graphs in the datasheet, like the chip is only capable of 100mA when you give it at least 5v... but in your case, it's not an issue, you're gonna have at least 6 volts.That's pretty much it... at least I think I got it right and I'm not writing something stupid.. it's 8 am here and I didn't sleep this night so I may be missing something obvious or making some mistake.

author: Six_Shooter
author_rank: Regular Contributor
timestamp: November 29, 2013, 05:53:59 am
content: Are you talking about LED replacements for exterior indicators or on the dash? I'm assuming turn signals here, but wondering if your terminology is a little different, because a 1920s car would not have OEM turn signals.

author: agilly1989
author_rank: Contributor
timestamp: November 29, 2013, 05:58:37 am
content: @mariush Would the Panasonic AN30888A-VF (found herehttp://au.element14.com/panasonic/an30888a-vf/led-driver-boost-buck-buck-boost/dp/2291453) be a better choice being a 3v to 20v input voltage driver?@Six_Shooter they are external turning signals and I'm only guessing that its 1920s

author: Six_Shooter
author_rank: Regular Contributor
timestamp: November 29, 2013, 06:09:48 am
content: This is actually very easy to do with only LEDs and a resistor (or few) per light. Running a pair in series and adding a current limit resistor will do the job. Better yet using 4 or 6 in a series/parallel to have more light will work just as well.If you take after some of the LED replacement lights that are made for tractor trailers, they use a small inductor to provide an inductive load that will work with conventional flasher units.

author: agilly1989
author_rank: Contributor
timestamp: November 29, 2013, 06:20:40 am
content: The problem is when and if my uncle upgrades the car from a 6v to a 12v system and since a lamp designed for a 6v system would burn out on a 12v system because everything increases (or decreases) as a ratio.Even if I chose to use 12v replacement bulbs they probably wont work (or would be super dull) on a 6v system so I'm trying to make his life as simple as I can by designing my lamp for 6v to 12v (basically 5v to 15v taking in account a flat battery on a 6v system and the system voltage of a running 12v system).Good idea though Six_Shooter but it would only really work on one system not both.

author: Zero999
author_rank: Super Contributor
timestamp: November 29, 2013, 07:05:44 pm
content: Quote from: mariush on November 29, 2013, 05:52:11 amHow about adding a buck converter to give 5V before the circuit?QuoteI love the simplicity of that IC. Not very modern ICs are as basic as something you can build from a single transistor and a couple of resistors and diodes.QuoteI agree with two LEDs on the output you won't get the rated output current with 6V in but it won't abruptly stop working. It'll be dimmer but may still be usable depending on the type of LEDs used. A 6V system will typically run at 7V with the engine running and 6.3V when stopped so it may be acceptable.

author: dannyf
author_rank: Super Contributor
timestamp: November 29, 2013, 07:21:10 pm
content: QuoteYou probably have to try.QuoteA LM317 would be more than enough, and I would use 1 lm317 to drive each of the leds - just to be safe.QuoteYou will need to consider the power dissipation on the LM317 (and the resistors, to a lesser extent). Assuming that you run the leds at 100ma per led - very bright, in my view. At 6v, the power dissipation on the LM317 would be (6-3.2)*0.1 = 0.3w - not a big problem, even with a small heatsink.At 12v, the power dissipation on the LM317 is (12-3.2)*0.1 = ~1w -> you have to use a fairly reasonable heatsink here.The power dissipation on the current-setting resistor will be 1.2v * 0.1a = 0.1w -> I would use a 1/4w or 1/2w resistor here.

author: strangelovemd12
author_rank: Regular Contributor
timestamp: November 29, 2013, 07:56:01 pm
content: Wouldn't six_shooter's solution be cheap enough to just wire for 6v and 12v, and tell your uncle not to forget to flip a switch over when he upgrades?

author: agilly1989
author_rank: Contributor
timestamp: November 29, 2013, 08:36:49 pm
content: what I might do is make a led tester just to see how bright the leds I chose actually are.4 AA batteries, a CC source (just to make sure I don't burn the cheap led out) and a way to hook up the led to the circuit.. maybe some leads and alligator clips.Thanks for the help so far guys

author: Corporate666
author_rank: Unknown
timestamp: November 29, 2013, 09:44:36 pm
content: Why would you want to use the MLE-AWT white LED for a turn signal? I am assuming you use yellow turn signals in Oz? Using a white LED behind a yellow lens is a bad idea - it is very inefficient, all you are doing is generating white light and then blocking almost all of that light except a narrow band of the yellow range.You would be better to use a yellow LED from the get go. Something like a Cree XBDAMB LED or a Lumilds LXM2-PL01 LED.Second, if you want something that will run on 6V or 12V, I would probably determine how likely the switch to 12v really is. I manufacture automotive electronics and everyone with a 6V system has a plan to move to 12V. But what is the point of upgrading to LED's shortly before moving to a 12V setup? I don't see the point of that... he should either stick with the 6V or upgrade to 12V then move to LED's. It sort of sounds like a case of "design gone wild" where every possible outcome is being accounted for - but designing for 6V and 12V just so it works for 6V for a short period of time is needlessly complex, especially for an aftermarket replacement that is being done by choice and not out of necessity.Having said that, if the 6V/12V thing is really necessary, I would design for 12V and make a 6V->12V boost module that you put inline while he is still running on 6V. There are just too many differences between 6V and 12V to make an LED system that runs on both without serious compromises.As for the LED's themselves... you can't test them with some AA batteries, even with a constant current setup. Any surface mount LED that runs above around 20mA uses the copper pads on the PCB for heat sinking - that incudes the Cree ML-E. If you solder wires to the LED directly, it will overheat in a matter of seconds when you run it at 150mA. To see its brightness, you really need to solder it to a PCB with large copper pours and appropriate heat sinking.I would say that even if you used the amber version of the Cree ML-E, two of them is seriously inadequate for a turn signal. You should be shooting for at least 200-300 lumens per signal of amber light (not white) minimum. I would go for 3 or 4 Cree XB-D's running at 350mA at a minimum, or maybe 10 ML-E's in amber running at 100mA or so. It's not really the best idea to run LED's at full current because they are much less efficient there - you can do it if you really need max brightness, but in a hobby project like yours where cost and size are likely not a huge issue, you should be more concerned with heat and longevity and err on the conservative side.As for the LED driver, look at the AP8803 from Diodes Inc. Super easy to use, wide Vin range, cheap, very reliable, etc. Make sure you put plenty of capacitance on the input, and a TVS at least for load dumps and transients.

author: agilly1989
author_rank: Contributor
timestamp: November 29, 2013, 10:03:09 pm
content: I recently talked to my uncle and he isn't planning to upgrade which makes my life easier.We do use amber/orange turning signals here in Australia, and the housing has an orange lens so I thought either white or amber/orange would do.I have next to no experience in lighting so I looked up some information, I saw that there was already a 12v 3W globe in the housing and what I saw from a google search was 16lm/W for an incandescent globe (48lm) so I worked off that :/ I was obviously incorrectSo I'm going to have to aim for 200-300 lumen in orange/amber light with good thermal design.Could I put an inductor on the input to "simulate" the effects of a incandescent so he wont need to change his blinker can?Thanks for the pointers Corporate666

author: Stonent
author_rank: Super Contributor
timestamp: November 29, 2013, 11:20:23 pm
content: I'd be tempted to use relays controlled by the 6V system that switch off and on 12V lights. Though once you get to this point you have to figure out how to keep the 12V system charged.What if we went about this from the other direction. Replace the generator / magneto (if not part of the engine) with a modern alternator and automotive regulator that charges 2 6V batteries in series. Use the full 12V for the lighting and tap off one of the batteries for 6V. Or use a standard automotive 12V battery with a high current 6V regulator.

author: Corporate666
author_rank: Unknown
timestamp: November 30, 2013, 01:36:16 am
content: Quote from: agilly1989 on November 29, 2013, 10:03:09 pmIs the move to LED's for extra brightness? Or reduced power draw? Or for the novelty of LED? Or all of the above?I am surprised the existing bulbs are only 3W - most blinkers in cars here use 1156 or 1157 bulbs which are 25W. If you are concerned about power draw, you could stick with the existing 3W draw, but the most efficient yellow LED's will get maybe 90 lumens per watt, so you would be lucky to get 250 lumens considering driver inefficiency, but that would be MUCH brighter than an existing 3W bulb, especially if the existing bulb is white (since it makes white light but most of that light is blocked by the yellow lens).So if you are going with the 6V system, I like the MLE LED's since they are still pretty efficient... the higher bins can achieve 90 lumens/watt at 150mA. I don't know how comfortable you are using surface mount parts, but a quick look at Digikey, and I would probably consider something like the Texas Instruments TL4242 boost LED driver.

author: Six_Shooter
author_rank: Regular Contributor
timestamp: November 30, 2013, 01:41:28 am
content: Quote from: Stonent on November 29, 2013, 11:20:23 pmWhy complicate matters?The 6V lighting would be pretty easy to deal with.The idea of using 2 6V batteries in series in a 6V vehicle has been used for many, many years, there are some compromises to the system though. The biggest benefit to doing that set-up is engine cranking. You use the 12V output of the batteries for starter motor, and run the rest of the car off the second battery (the one that has the direct connection to the chassis).

author: agilly1989
author_rank: Contributor
timestamp: November 30, 2013, 02:07:55 am
content: Quote from: Corporate666 on November 30, 2013, 01:36:16 amThe move is because its an old bayonet style lamp, and being able to find new replacement bulbs locally is hard. So, I suggested LEDs because they are more efficient and they last longer (especially when used at currents lower then their limit).2 photos of the housing belowhttps://www.dropbox.com/s/g8yu9ll9tdwd9vc/2013-11-30%2012.54.45.jpghttps://www.dropbox.com/s/1nu144bjnom1yo4/2013-11-30%2012.55.10.jpgI was going to design the board in such a way where the "heatsink tracks" would make their way to the mounting point on the housing, so that would help with the thermals a bit considering there would be fresh air flowing over the housing when the car is in motion.

author: Six_Shooter
author_rank: Regular Contributor
timestamp: November 30, 2013, 03:15:13 am
content: As I suspected those are add-ons at a much later date, likely due to legislation requiring all cars to have them. I know what some of you Aussie's go through to get your cars on the road, especially older and modified cars. I'm glad I don't have to deal with that.I'm going to STRONGLY suggest keeping this simple, I would forget about LED drivers or any active circuitry, it's simply not needed. You won't need to worry about any thermal conductance or provisions. I've also seen many LED conversion systems available that use active circuitry (such as the sequential tail light conversions) that fail in short time, for various reasons.The other thing to consider is that IF your family member ever does swap to a 12 volt charging system, modifying or replacing the LED conversion you are doing now will be the least of his worries, there's so many other components that will need changing that, these would just be one small part of the check list.Have you considered how you're going to get the turn signal flasher to function? Most flashers use the load of the bulbs on to heat up a bi-metal contact and is what causes the flasher to actually function. This is where a small inductor placed in parallel with the circuit is sometimes needed as I mentioned previously. You can get flashers for LED systems and for combination LED/conventional bulb systems as well.Many times the simplest solution is the best.

author: Corporate666
author_rank: Unknown
timestamp: November 30, 2013, 04:26:14 am
content: Quote from: Six_Shooter on November 30, 2013, 03:15:13 amIn general, I have to disagree with this....Consider a standard 12V system. Many people say "just pick the right value resistor and away you go".Ok, so let's say you have an LED with a forward voltage of 2.4V and If of 100mA. A car electrical system can vary from maybe 10.4 volts when off to 14.5 volts when running. So if you wanted to run a string of 4 LED's... what resistor value do you choose?4 LED's is Vf of 9.6, so let's say you choose an 8 ohm resistor. At your lowest voltage, you are getting 100mA and things are good. But when you turn on the ignition and the voltage goes to 14.5, now your LED's are running at 600mA and they blow up. If you choose your resistor value based on your maximum voltage of 15, that would be say 54 ohms for 100mA for your 9.6 forward voltage LED string. But now at 10.4 volts, you're only getting 15mA through your LED's... when you start the engine and the voltage rises to 14.5V, now 90mA is flowing through your LED's. That is a very big difference and will be very noticeable - it will make the LED's look much brighter when the engine is running.Now I realize you were not suggesting he just use a simple resistor, but in case you were, I have to say I disagree with that.And when you consider that a chip like an RT8472 is $0.25 and needs only a capacitor, diode and inductor to run and is constant current and offers PWM of voltage level dimming, I think there's little reason to go with that solution. Total parts cost is something like $0.65 exclusive of the LED, probably equal or cheaper than any linear solution, plus you get dimming and it's a switcher so much more efficient and less heat - and heat is always an issue with higher power LED's anyway, so there's no sense in making the heat issue even worse by burning power as heat with a linear solution.Active solutions are super simple, cheap and easy to implement. Plus it's the right way to drive LED's. There's no reason not to do it that way other than fear of the unknown, IMO.

author: Six_Shooter
author_rank: Regular Contributor
timestamp: November 30, 2013, 05:04:51 am
content: Quote from: Corporate666 on November 30, 2013, 04:26:14 amConsidering I've done this on MULTIPLE occasions, I know it works EXTREMELY well. You can do all of the math you want, but in practice the intensity of the LEDs varies little between engine off and running, most people would not notice the difference. If your 12V battery is resting at 10.4 volts it's dead and you need to replace it. A 12V car battery should rest at 12.6V fully charged with no load. In practice it will usually sit about 12.4 to 12.5 due to some parasitic drain for some of the on board electronics, and should never go over 14.4 volts when charging. If the voltage goes higher then the regulator is shot failing or failed and needs to be replaced. But we are talking about a 6V system here., resting voltage should be around 6.3 volts and should not reach much beyond 8 volts when charging, if it ever gets that high, I know my Grandfather's 40 Dodge that has a 6V system barely gets that high.You want dimming? Add a resistor and diode to the circuit to give dual brightness for running light and turn signal. You really need to look at the available LED replacement lights on the market, very few, if any actually use anything more than a resistor or two and sometimes an inductor (to simulate load), that I have used or seen."The right way" is subjective, since a correct way to have this work is to simply use a resistor that will limit current based on maximum voltage the system will attain, works very well as I have said.

author: agilly1989
author_rank: Contributor
timestamp: November 30, 2013, 05:53:52 am
content: I would honestly feel better and safer using a constant current source. Knowing the LEDs are running at the right voltage and current would make me more comfortable

author: Corporate666
author_rank: Unknown
timestamp: November 30, 2013, 09:14:03 am
content: Quote from: Six_Shooter on November 30, 2013, 05:04:51 amWell, there is a reason not a single OEM has ever used a simple resistor on an unregulated LED on any automotive application in the history of automotive applications - because it's shit design - period. There are lots of people who build unfused stuff that they run on mains and say it runs "fine", but that doesn't mean it's good design. And it's indisputable that adding heat to a system where you are trying to manage heat is a bad idea.When you are using LED's that require a custom PCB anyway because they use the PCB tracks for heat dissipation, there is really zero reason not to use the correct approach other than not being knowledgeable in the right way to do it. But it's not hard to do or expensive to do, so may as well do it the right way. It's more electrically efficient, it's more thermally efficient, it will make the LED's last longer, it will simplify thermal design and it's the reason LED drivers exist in the first place.When you are trying to be efficient and string LED's together to get a more reasonable Vf, it's even more important.The right way really isn't subjective. The SAE in the USA publishes documents which state the standards which should be met, and each country has their own. That doesn't mean the hobbyist needs to stick to the letter of the standard, but flaunting them with known shoddy design is a bad idea as well, especially when good design is so easy and trivial in comparison.I think you really need to look at what the reputable manufacturers like Koito, Stanley, Sylvania and such are manufacturing. I've opened up hundreds OEM LED headlights, tail lights and turn signals and I have never seen a single one that uses just a resistor right off 12V.

author: agilly1989
author_rank: Contributor
timestamp: November 30, 2013, 09:54:37 am
content: SO... Just so I get things straight...That RT8472 could run 2 x 2.5v 350mA Cree XP-C LEDs from a 6v source without issues?My Current BOM (Feel free to criticize it)6 x Cree Amber XP-C LEDs (XPCAMB-L1-R250-00401)3 x Richtek RT8472Total estimated lumen output at 350mA/LED is 330lm(Passive components to suit)Also, how would I calculate total current draw? I realize it'll be bugger all but it would be useful for correct fusing for the circuit

author: BravoV
author_rank: Super Contributor
timestamp: November 30, 2013, 10:23:06 am
content: Quote from: Corporate666 on November 30, 2013, 09:14:03 amHundreds !!Just curious how many 12 volt based led lights you've built ?

author: dannyf
author_rank: Super Contributor
timestamp: November 30, 2013, 02:04:37 pm
content: QuoteMost simple buck converters can be configured as a constant current drive (like 33063 for example, or even a 555). Or other dedicated led drivers are a fair bit more common than this particular one.

author: Corporate666
author_rank: Unknown
timestamp: December 01, 2013, 12:44:38 am
content: Quote from: agilly1989 on November 30, 2013, 09:54:37 amThe RT8472 is a great LED driver that I've used many tens of thousands of with excellent success in automotive applications, and it is incredibly cheap! But I don't think it would be well suited to your particular application - it is a buck (step down) driver, with a 5V to 30V input range, so you would be running really close to it's cut-out voltage and it won't be all that efficient, and you would only be able to drive one, maybe two LED's with it.Instead, I would probably go with the Texas Intruments TPS61165. With just 3 capacitors, an inductor, a diode and a resistor, you're good to go - it will accept 3V to 18V input and it is a boost regulator, so it will step the voltage up, allowing you to run pretty much as many LED's as you want. And if you ran, say, 10 LED's in a string, you will get into the 90-95% efficiency range so the driver circuit will run nice and cool. And not only is the driver cheap, TI will send you some for freeand their datasheets are awesome (IMO) and they basically give you a parts list and a PCB layout. You can run the LED's at lower current (like 100mA or even a bit less) for more efficiency as well as more even light distribution within your housing. Then you could just put the driver circuitry on the back of the same board, fill it with copper pours, do some testing to see what you can get away with for max drive current and you're good to go.The other nice thing about this setup is that LED current is set with a resistor so you can use a precision 10-turn pot if you like, or use a trimpot in conjunction with a normal resistor so you can adjust LED current precisely in small increments, and then test it in the housing while you let it blink on your bench for several minutes at a time and see what temperature it reaches.Keep in mind it's the LED junction temperature that matters - on the MLE's it's probably 150C but you won't want to get anywhere close to that - but even staying below 50C board temp, I bet you get massively more brightness than a 3W incandescent bulb.

author: agilly1989
author_rank: Contributor
timestamp: December 01, 2013, 12:55:12 am
content: That looks like a good and simple chipI will be doing Copper Fill on both sides of the board to help with heat dissipation and the housing will be part of the thermal-path as well (just to help), so thermals wont be too much of an issue AND since its an indicator, it'll be flashing, so its not on ALL the time.Thanks for the tips guysI'll post pictures when I make it

author: Corporate666
author_rank: Unknown
timestamp: December 01, 2013, 12:57:31 am
content: Quote from: BravoV on November 30, 2013, 10:23:06 amThanks for the vote of confidenceJust to clarify, the ones I have opened were not ones I designed myself, but I have designed dozens of automotive turn signals and tail lights that we have sold tens of thousands of and we don't just use resistors, but what do I knowThe other bad part about using resistors is that in the case of the LED cited - the Cree ML-E... all of these LED's are thermally limited. So a Cree ML-E may have a Vf of 2.4 and an If of 0.15A. So that's 0.36 watts. Some of that turns to light, but even in an efficient LED, about half of that will be heat - that is about 0.2 watts of heat to handle.In the proposed 6 volt system, 2 ML-E's in series would be 4.8V, so we have to drop 1.2 volts at 0.15A. That's an additional almost 0.2 watts of heat. Well, considering lighting designers biggest challenge is heat management and the 0.2 watts is quite a challenge to overcome, then adding another completely unnecessary 0.2 watts for absolutely no reason other than pure laziness makes no sense at all.Yellow LED's are the worst when it comes to degradation of light output from temperature. Page 7 of the Cree ML-E datasheet illustrates this perfectly - the amber ML-E loses90%of it's light output at 150C that is has at 25C. So keeping the LED as cool as possible is the #1 priority.Using resistors to control current which burn up the voltage as heat is a fabulously bad idea

author: agilly1989
author_rank: Contributor
timestamp: December 01, 2013, 02:51:19 am
content: Either I'm thinking straight or I just don't know but if I was to run 3x 100mA LEDs in series, would I need 300mA or 100mA or some other amount?

author: mariush
author_rank: Super Contributor
timestamp: December 01, 2013, 03:24:11 am
content: 3 in series = 3 x voltage, same current3 in parallel = 1x voltage, 3 x current

author: agilly1989
author_rank: Contributor
timestamp: December 01, 2013, 03:27:15 am
content: thanks mariushI thought that was the case.Just to make sure, if I was running 6 (2 sets of 3) it would be 3 x voltage and 2 x current, right?

author: agilly1989
author_rank: Contributor
timestamp: December 02, 2013, 03:28:38 am
content: I can see what you mean by TI having awesome data sheetsit basically tells you exactly how to configure it.It was a little confusing at start but I think I have got the equations right.

author: agilly1989
author_rank: Contributor
timestamp: December 02, 2013, 04:44:00 am
content: I am now confused :/ I'm working out the "Thermal Considerations" for the TPS61165 and the equation is as followsPD(MAX)= (125-TA) / R(JA)PD(MAX)= Maximum power dissipation limitTA= Maximum Ambient Temp = 80ocR(JA)= Thermal resistance Junction-to-ambient from the table = 210.1which gives me the answer for PD(MAX)as 0.21418372I don't know if that's a good answer or not

author: pickle9000
author_rank: Super Contributor
timestamp: December 02, 2013, 05:13:55 am
content: These are for flashlights, yes I know ebay sucks.http://www.ebay.ca/itm/Cree-XLamp-XM-L-XML-EasyWhite-LEDs-T6-7B-3200K-Warm-White-6V-16mm-Board-/321145897333?pt=Motors_Car_Truck_Parts_Accessories&hash=item4ac5c98175&vxp=mtr

author: agilly1989
author_rank: Contributor
timestamp: December 02, 2013, 05:40:24 am
content: It really doesn't matter about what LED (or LEDs) I use as long as they are amber or orange and can give off 300ish Lumens of output (total).The driving of said LEDs is the thing I'm mostly worried about. Making sure the driver is stable, efficient and suitable for this application. Having it in the enclosure on a hot Aussie day, the internal temp could hit 80oC or higher so making sure the components wont melt and let the magic black smoke out is a priority.Now... I'm no thermal design professional or anything, but I do know, the more metal connected to a hot device the better.More LEDs would probably be better (mainly for better light distribution) but it possibly wont matter as much because the lens is diffused... So yeaThe 6 Cree XP-C LEDs when running at 250mA (100mA less then the tested current) will still give 231lm which I'm happy with. Having them run at that temp will make them run a bit cooler hence last longer.