Looking for a specific DC CC driver for LEDs

theatrus said:
Looks like I fitted it with the LM3409HV, which puts the next limit on the FET (60V) and the input filter capacitors (50V). The input filter capacitors are the most concerning. Running at 60V should be ok for short periods of time - it would need to be restrapped for 100V caps (at a much higher relative cost) and larger footprint of those for long term operation.

Current limit is set with a 0.080 shunt which is ~ 3A. Going to ~5A is easy. This design still requires swapping the shunt (a 2010 footprint SMT part) to increase current. If it was re-strapped for 5A operation, you can use the analog (0-1.2V) dimming port to drop the peak current to other levels, which is a design I'm messing with right now.
Click to expand...

So.. Since the chip's peak voltage is probably 48V at 2.5A, if I try running 3A through it, it would probably run up to 50V and might damage the LED? What's the easiest way to walk up the current on your board without a PWM?

If needed, I can get my Arduino up to it, but I just wanted to get the board up and running first.
 
The peak current delivered currently is 3A, average current will be less.

The easiest way to actually control peak current is to provide a 0-1.25V input to the Iadj pin which is broken out on the board (not on a header) (*with a several K series resistor to avoid an alternate ground path if the main ground is disconnected and it's not an isolated supply - ask me how I figured this out :-D*)

A 1.5A AA battery and a potentiometer would be a great way of tweaking it and doing a very gradual ramp.

This is superior to the PWM approach as the actual peak current will be limited and not just the duty cycle of the full 3A peaks.
 
karimwassef said:
Another interesting consideration:

If I had just assumed the part was as spec'd and set the output voltage to 34V, it would have only pulled 0.7A and generated ~25W.

If I has set my current source to 3A, it would have run to ~45V and generated ~135W.

One of the complexities here may be that using these chips require individual re-characterization to determine where they can run. That's ok for a DIY, but probably worthless for general industrial use.
Click to expand...

That's why these chips are only $5, no one could use them for any decent commercial application without first testing and "rebinning" each one.

As you probably know with LEDs being a diode the forward voltage drop limits the current to the chip(s). As voltage is increased so is current across the LED.

I don't have an explanation for the very odd behavior you noted on your white LED multichip test, something is wrong, either the LED or the driver is behaving badly.

Normally a driver limits the current to its "set point" by regulating the voltage up or down as needed within it's designed range in order to maintain the set current output to the LED. When the attached array is trying to exceed or draw less than the drivers designed voltage range at the set current then all sorts of strange things can happen (probably explains all the strange things you were seeing).

Simplest way to bench test and "bin" your chips that are out of expected range would be using a nice simple adjustable voltage supply. If you had a meanwell CLG or HLG 'A' model with sufficient amperage and voltage range that would be an ideal testing power supply as it can be used to provide both voltage limiting or current limiting with in a pretty broad range. They are a bit pricey but really handy to have around for such tinkering.

It is highly unlikely that a multichip using 10x series/parallel configuration should ever reach 50 volts without well exceeding the current it's rated to handle (typically 350mA per string, added up for each parallel string in the array (sometimes 700mA but pretty uncommon)).
 
I'm with zachts that the numbers don't make a whole lot of sense as there is a significant normal ohmic component to them. Something in the system is influencing the shape of that curve outside of expectations.

I'll have some time to characterize my $10 RB LED soon which can hit 100W at 34Vf (still out of spec, but not a whole mile out of spec). I can run it on two ganged HP 6644A supplies (60V/3.5A) with remote sense.

Welcome to China Shenzhen Market Specials :)
 
theatrus said:
I'm with zachts that the numbers don't make a whole lot of sense as there is a significant normal ohmic component to them. Something in the system is influencing the shape of that curve outside of expectations.

I'll have some time to characterize my $10 RB LED soon which can hit 100W at 34Vf (still out of spec, but not a whole mile out of spec). I can run it on two ganged HP 6644A supplies (60V/3.5A) with remote sense.

Welcome to China Shenzhen Market Specials :)
Click to expand...

Wait... yours has the same characteristic??
 
zachts said:
That's why these chips are only $5, no one could use them for any decent commercial application without first testing and "rebinning" each one.

As you probably know with LEDs being a diode the forward voltage drop limits the current to the chip(s). As voltage is increased so is current across the LED.

I don't have an explanation for the very odd behavior you noted on your white LED multichip test, something is wrong, either the LED or the driver is behaving badly.

Normally a driver limits the current to its "set point" by regulating the voltage up or down as needed within it's designed range in order to maintain the set current output to the LED. When the attached array is trying to exceed or draw less than the drivers designed voltage range at the set current then all sorts of strange things can happen (probably explains all the strange things you were seeing).

Simplest way to bench test and "bin" your chips that are out of expected range would be using a nice simple adjustable voltage supply. If you had a meanwell CLG or HLG 'A' model with sufficient amperage and voltage range that would be an ideal testing power supply as it can be used to provide both voltage limiting or current limiting with in a pretty broad range. They are a bit pricey but really handy to have around for such tinkering.

It is highly unlikely that a multichip using 10x series/parallel configuration should ever reach 50 volts without well exceeding the current it's rated to handle (typically 350mA per string, added up for each parallel string in the array (sometimes 700mA but pretty uncommon)).
Click to expand...

So I ran it for a couple of days with no deviation in performance: 44.1V and 3.03A = 134W. I could go up and down the voltage and current without issue. It's only when I pushed the voltage over 48V that I saw degradation.
 
karimwassef said:
So I ran it for a couple of days with no deviation in performance: 44.1V and 3.03A = 134W. I could go up and down the voltage and current without issue. It's only when I pushed the voltage over 48V that I saw degradation.
Click to expand...

At a certain point no amount of cooling will prevent damage occurring on the diodes, it would be like trying to run a 20,000 btu window AC unit plugged into an extension cord made of 18 gauge wire........the damage and degradation happens even at low current, just very slowly, the harder you push the diodes the faster the degradation occurs until instantaneous failure occurs at a certain threshold.
 
sure.. the question is where that point is.

Keep in mind that this is 100W chip that was able to run at 180W... is 120W viable for 12 months? 160W?

I need to talk to some engineers at work about relating accelerated testing to failure to real use reliability (1 hr to failure at 180W = 10,000 hrs to failure at 120W ... or something like that).
 
karimwassef said:
sure.. the question is where that point is.

Keep in mind that this is 100W chip that was able to run at 180W... is 120W viable for 12 months? 160W?

I need to talk to some engineers at work about relating accelerated testing to failure to real use reliability (1 hr to failure at 180W = 10,000 hrs to failure at 120W ... or something like that).
Click to expand...

Something like that but "failure" isn't exactly always dead with LEDs, it's usually a loss of 30% initial intensity, at least when looking at manufacturer ratings under the test parameters. look at it this way, if you wan't 180 watts for 6 months you are way better off running two 100 watt chips at only 90 watts. they will retain much higher out put after that 6 months. the one chip running at 180 watts might still be lit up after 6 months but it will be a tiny fraction of it's original brightness, how much less depends on far too many factors to speculate without reliable spec sheets, especially when talking about pushing the chips well over their "rated" limits.....run three of them at 60watts each and they may well last a life time, or at least longer than you care to resist swapping them out for something new and more exciting........

Sure, just for fun I've pushed 350mA ebay special diodes to over 1.5 amp current for hours at a time with no catastrophic failure, but that kind of abuse exponentially reduces output and efficiency, so much so that the little sacrificial diode of my experiment would no longer illuminate with the 2xAA battery tester after a couple hours, It still lit up with the driver but I forget how high the Vf had gotten, it was a long time ago..........
 
If I can keep the LED backplane chilled at 50F (10C), I would only have to worry about the thermal gradient to the semiconductor inside.

I did mention that I'm using liquid cooling with chilled fluid.. didn't I? :)

<a href="http://s1062.photobucket.com/user/karimwassef/media/F7C67B19-617F-43B9-89DA-AD1AEF79B1EE_zps2btckmf2.jpg.html" target="_blank"><img src="http://i1062.photobucket.com/albums/t496/karimwassef/F7C67B19-617F-43B9-89DA-AD1AEF79B1EE_zps2btckmf2.jpg" border="0" alt=" photo F7C67B19-617F-43B9-89DA-AD1AEF79B1EE_zps2btckmf2.jpg"/></a>

<a href="http://s1062.photobucket.com/user/karimwassef/media/909058BE-A2F0-4551-8DD1-EDDB0FFCD4E6_zpsecf5ahlz.jpg.html" target="_blank"><img src="http://i1062.photobucket.com/albums/t496/karimwassef/909058BE-A2F0-4551-8DD1-EDDB0FFCD4E6_zpsecf5ahlz.jpg" border="0" alt=" photo 909058BE-A2F0-4551-8DD1-EDDB0FFCD4E6_zpsecf5ahlz.jpg"/></a>

<a href="http://s1062.photobucket.com/user/karimwassef/media/2FA7A93C-0095-44C8-AE6D-376AAA66F8B5_zpsufqh4iy7.jpg.html" target="_blank"><img src="http://i1062.photobucket.com/albums/t496/karimwassef/2FA7A93C-0095-44C8-AE6D-376AAA66F8B5_zpsufqh4iy7.jpg" border="0" alt=" photo 2FA7A93C-0095-44C8-AE6D-376AAA66F8B5_zpsufqh4iy7.jpg"/></a>

<a href="http://s1062.photobucket.com/user/karimwassef/media/393F1028-EFD8-43BB-9515-447EAF9FED18_zpsto6ybiwa.jpg.html" target="_blank"><img src="http://i1062.photobucket.com/albums/t496/karimwassef/393F1028-EFD8-43BB-9515-447EAF9FED18_zpsto6ybiwa.jpg" border="0" alt=" photo 393F1028-EFD8-43BB-9515-447EAF9FED18_zpsto6ybiwa.jpg"/></a>

It's a two stage chiller actually. The first brings the water down to room temperature. Then the Peltier chiller drops it lower.

Still need to experiment, but that's a whole other thread.
 
Last edited:
theatrus said:
This may help. Tj will be elevated of course:

http://www.ledjournal.com/main/wp-c...Understanding-Power-LED-Lifetime-Analysis.pdf

Add in the fact that these currents are all rated (not overdriven) and from qualified LEDs, not ones found in the dumpster.
Click to expand...

Great paper - my conclusion is that keeping the junction temperature under 100C should allow me to run at any forward current I want. :D

Now all I need is the thermal impedance from the copper back to the junction.
 
karimwassef said:
Great paper - my conclusion is that keeping the junction temperature under 100C should allow me to run at any forward current I want. :D



Now all I need is the thermal impedance from the copper back to the junction.
Click to expand...


Due to thermal resistances this isn't possible. Even with it immersed in liquid N2 ;)

Good luck finding a real C/W reading - we don't even know who made these. If you were on the ground in Shenzhen (fabulously interesting place) and had a native mandarin speaker with you there is some hope of finding the data sheet.
 
Actually, I have plenty of friends and colleagues who match that description. I also like Shenzhen- great seafood and only a short ferry ride away from HK.

A tad industrial though :)

I doubt that these particular chips deviate much in terms of thermal properties from normally good chips. They're rejects from the same lines - unusable by industry but should be adequate for my uses.

I'll start by finding published C/W for these kinds of chips - maybe a distribution can help. I also have a Chinese contact in one of the factories, but he may not have this kind of data.

If I get no leads, we could cross-section one to get a measure of the thickness and materials in the construction. Maybe cross section a few. Well, not the expensive ones I plan to use in my final setup- those are $160 a chip. :)
 
ghjgh said:
don't see one there, but it sure looks like you want something similar to those that I posted to put out 3x the mA they do.
43.gif

37.gif

39.gif
Click to expand...

? Don't follow.

Someone decided to overclock CPUs and GPUs and it created a world of DIY chilled computing applications. There was once a time where even thinking of doing that was laughable.
 
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