7135 drivers with higher voltages revisited

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Rufusbduck
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At one time I was a Boy Scout and some vestiges of the motto still cling to my behaviour. I feel compelled to admit that one xml and 8 additional 7135 have given their all for the sake of knowledge. All was going well, I had 8 chips soldered into a piece of cu being controlled by my special controller board(no 7135’s, just atmel and 7805)powering 4 xml’s. With 10 series nimh’s I was getting all modes and 1.4A on high(Vbatt < Vf). I added 2 more nimh’s for a no load voltage of 15.3V and used a 1/2 ohm 2W resistor in series with the leds and measured 2.08A on high and the chips were still cool so I removed the resistor from the circuit. I started on low mode, all fine, chips cool, the med, still good, chips cool, when I went to high first one xml went out then the modes still functioned but at very low levels. I believe when the xml went, the remaining voltage to the 7135 chips jumped up to ~5V and they went poof! Here is a picture of the driver setup showing the chips loaded with the ground post and Vdd wire in place
And here with the pwm controller added(I cut off the portion of the board that had 2 empty 7135 pads)

So far in all of the tests the controller portion has worked perfectly and has survived each time. On the first sink I added some extra cu after the chips were loaded. In this case I forgot to solder the ground wire to the sink in advance of loading the chips and this may have proven costly. Soldering to the pins after the chips are loaded is no problem but any soldering done on the sink needs to be finished first before the chips go on. In any case, my reflow skills need improvement(as does my memory). I do not know for sure if this has any relavance but some of my “failure analysis” has noted a lack of current control in the 7135 chips afterwards. I have removed the wires and cookies(cooked chips, lol) on the sink and will try to reload them this week. I may just be making excuses as I am reluctant to call this idea “busted” but this is certainly a setback.

Three Tanna leaves to give him life, nine to give him movement. But what if he eats the whole bag?

Scott

Techjunkie
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The thing that appealed to me most about your end goal was that it could add some flexibility to a simple, affordable solution. At this point, it is no longer simple, and the heatsinking makes it less affordable. I’m compelled to ask, is it just the challenge of it, or is there some reason for a strong preference for a 7135 based solution instead of DC-DC buck circuit?

Rufusbduck
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Probably just stubborn and don’t want to quit yet. Here are the reasons I started investigating these boards: I’ve used the KD super P7 driver but they suck for efficiency. Sharkbucks cost twice as much as the KD driver and don’t work they way I would like and the B-flex and Der Wichtel are cost even more and are too big. The Sharkbucks is the only 3A buck driver close to the size of a 105C but if I can make this work it will be small, close to 90% avg efficiency, still cheap($4/chips, $3/ board, $.50 regulator, $3 resistors, and the sinks are made from scrap cu) so similar to KD but more efficient and in spite of the trials and tribulations I’ve gone through it is still simple to do.
If you are willing to have an on-on-on-off switch with 2 resistors(1.2 ohm, .6ohm), you can use a 3A 7135 board with just the voltage regulator addition to drive 4xml in series. That part is done and proven. I’m being stubborn about the resistors(don’t want them) and my testing is to see how much heat sinking is practical for ME. I’m not yet adept at reflow and this has cost me some chips and aggravation but I’m not quite ready to cash it in yet. Who knows, it may end up that it works fine but I’m just doing it wrong.

Three Tanna leaves to give him life, nine to give him movement. But what if he eats the whole bag?

Scott

Rufusbduck
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sixty545 wrote:

Sorry, I have not read the whole thread carefully but the way I understand this, in a PWM situation the voltage across the 7135’s can switch between 0V and 16.8V.
Have you considered that the 7135 are only specified to 7V max ?

Well, this could easily be remedied by a zeener diode across the 7135’s (z6.3V or like) to limit the voltage so I think that your circuit is sound enough.

If it is the case that these spikes are the/a problem rather than my at present poor reflow skills then the Zener diode might provide a solution. Would a resistor also be needed to limit the current. I don’t really like the idea of a resistor permanently part of the drive circuit this way.

Would a capacitor be able to capture this power and bleed it off through a resistor during the Zener-inactive cycle.?

Could the Zener output be connected to the Vdd trace of a separate 7135 with another 3.3V Zener back to the 7135 output turning wasted power into light?
The duty cycle migh need reprogramming to maintain desired light output levels.

If it seems I am easily diverted you’re right but please remember that I have a definite goal in mind. I just want to learn things along the way.

Three Tanna leaves to give him life, nine to give him movement. But what if he eats the whole bag?

Scott

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to be honest, after using both 7135 based and Taskled drivers, if you’re going to be spending $40+ in LEDs and similar on a battery, $3-40 on a decent driver is a pretty good investment. The programmable UI, temp and undervolt warnings and amazing customer service are easily worth the premium over a $5 driver. If you’re really strapped for space, why not an Lflex with the 4 XM-Ls run in 2S2P with the driver set at 3.5A for 1.75A per LED? That’s right in the middle of the XM-Ls efficiency curve and any housing that won’t fit a b3flex also won’t dissipate the 40W plus that 4 XM-Ls @3A will generate.

I can see the appeal in forging your own path, but sometimes it’s worth ponying up the extra and spending that time relaxing or using the light instead Wink

Rufusbduck
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It’s not really about the money at this point. I have 2 quad xpg lights that have Maxflexs installed, 2 tri xre lights that use the KD super P7 driver, and another with a B3flex partly awaiting LEDs. Lflex is an option even though it has the same heat issues as 7135 based drivers(uses an fet instead I think) but all of Georges’ flex drivers use a momentary switch that requires separate wiring of limited length. The XML example is more likely to end up in a dive light where heat is not a problem. In the end , I’m doing this because I want to and my curiosity has not succumbed to my attention span.

Three Tanna leaves to give him life, nine to give him movement. But what if he eats the whole bag?

Scott

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Here are the latest results from this set up:
12V battery(10-sub c nimh cells in series).
3-XML U2 LEDs in series.
1-DX 7612 board with 7135 chips removed and 1-78L05 installed.
8-7135 chips stripped from 7612 board and 1A 1-mode boards and reflowed to custom (lol) heat sink.
1-Judco switch with 2-1ohm resistors in series.
On low using both resistors I measured .102A, 13.45Vbatt,13.43V after resistors, 7.3V across the 3 emitters, and 5.6V across the 7135’s.
On medium with 2 resistors I measured 13.40Vbatt, 12.29 after resistors, .707A, 7.6V across emitters, and 4.1V across 7135’s.
When I switched to high I read 2.37A but the resistors began to smoke so I switched back to low.
It has been running continuously on low since then which is when I began typing this post(~1 hr) so I don’t think pwm voltage spikes are a problem at this output level.
The resistors were both supposed to be .5 ohm resistors but some readings don’t seem to be consistent with that value. Also a cheap DMM. Of necessity I’m getting better at both stripping and reflowing chips but I (and you as well, sorry to say) will be waiting for the full power test until I have higher wattage resistors in place. I’m going to run it on medium for awhile and let you all know the outcome of that after work tomorrow.

Three Tanna leaves to give him life, nine to give him movement. But what if he eats the whole bag?

Scott

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interesting results, looking forward to the High results with the beefier resistors. Looks like the 7135s are getting the right voltage on medium but a rather low Vf – is that normal for that current draw (0.7A)?

I hear what you’re saying about the pull of curiosity! You’re clearly not doing this out of necessity Smile

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The goal at the outset was for 4 LEDs powered by 4 Li-ion and though I’m very pleased with how the 7805 is working I’m not overly confident about the 4×4. 2s2p I think is very plausible and 3×3 would be great. What to me makes this idea questionable is if you forget where a switch is set you could blow all the 7135’s by accident. Even if I can make it work, this represents a serious flaw. Oh well, one set of chips a week is less than popcorn money. To some I’m sure this seems a pointless exercise but it has been good practice and has taught me how to make a custom heat sink for the chips allowing installation in odd places. In any case it ran without incident on medium for another 20 minutes by which time Vbatt had dropped to 9.3V(recovered to 11.1V).

Three Tanna leaves to give him life, nine to give him movement. But what if he eats the whole bag?

Scott

Rufusbduck
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Also, the voltage measurements may be suspect since I am measuring a pwm signal which may not correspond to a current vs Vf curve. I use a lot of big words but I really don’t know s**t. Time for a beer.

Three Tanna leaves to give him life, nine to give him movement. But what if he eats the whole bag?

Scott

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I’m going to try this mod on 4 LEDs 2s2p with 8.4 V. Since the 78L05 requires ~2V overhead I ordered some LD2981 very low dropout regulators from Mouser which will stay in spec down to full discharge. Also ordered were some smt 0805 1 and 2.2 micro farad ceramic caps.

Three Tanna leaves to give him life, nine to give him movement. But what if he eats the whole bag?

Scott

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I think I may have discovered a relavant tidbit. When I tried this with the pack fully charged to 14.3V the chips died(gates lock open and can’t be dimmed). Remember, on low and medium I was measuring 7.3v – 7.6v across the emitters so the fresh pack was exceeding 4V across the chips even with the resistors. Even though the chips don’t even get warm on low and medium, they poof at to high an input V. I went over the 3 nimh/1 Li-ion per led limit. If this is the case, then 4 LEDs on low-med at ~10v and high at ~13.2v would stretch the ability of a resistor to both lower the voltage sufficiently for safe operation on low-med and maintain voltage s above Vf on high. At this point 2s2p might prove more reliable which is the reason for the Mouser order. For my next magic smoke, I’ll reload the sink with fresh chips and run the test again with 9 nimhs. For the record, I still haven’t spent enough on toasted chips to buy even half of 1 quality Taskled or Shark driver.

Three Tanna leaves to give him life, nine to give him movement. But what if he eats the whole bag?

Scott

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It may appear that you are talking to yourself, believe me when I say Ive followed this with interest even though I dont understand it. I may learn something if I'm lucky. Keep it up and good luck with the outcome.

 

djozz quotes, "it came with chinese lettering that is chinese to me".

                      "My man mousehole needs one too"

old4570 said "I'm not an expert , so don't suffer from any such technical restrictions".

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Thanks, it does seem that way but I notice that some are reading( or at least looking at) this thread. Watching someone muddle through isn’t how textbooks are written but at least it’s genuine. Posting just the end result would be better as a “How Too” guide and I hope to get to that point but this is more of a journal.

Three Tanna leaves to give him life, nine to give him movement. But what if he eats the whole bag?

Scott

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I follow your so-called "muddling through" with scrutiny every day Rufusbduck

And I start to see some relevance to it too so keep it up. You are doing a hell of a job and I hope you will nail it in the end. Sure makes for some exciting reading Smile

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I appreciate the vote of confidence. Heading home tomorrow to muddle some more. I have an XTE quad pcb with a 2s2p jumper option that I will set up on a cu cap to be ready when the new regulator chips come. This will use 2 sets of 4 chips each controlled by one Atmel chip(equivalent to 1-1.4A master and 1-1.4A slave). Testing for this will be later in the week.

Three Tanna leaves to give him life, nine to give him movement. But what if he eats the whole bag?

Scott

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I’m still following and it’s still interesting! Always cool to see an experiment in process, even if I only partially understand what’s going on and almost definitely wont benefit from the outcome Smile

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I just spent the last 1 1/2 hrs typing and my iPod just dumped it all $&@%#*€¥. I’ll repost tomorrow but suffice to say it works just fine in all modes with no added resistors.

Three Tanna leaves to give him life, nine to give him movement. But what if he eats the whole bag?

Scott

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Your being polite, not. I know the feeling well.

 

djozz quotes, "it came with chinese lettering that is chinese to me".

                      "My man mousehole needs one too"

old4570 said "I'm not an expert , so don't suffer from any such technical restrictions".

Old-Lumens. Highly admired and cherished member of Budget Light Forum. 11.5.2011 - 20.12.16. RIP.

 

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Got home at night and loaded the heat sink with 8 new chips reflowed with Kester solder paste and reattached the mcu board, put 2 series 1/2 ohm 2W resistors in parallel with a 1 ohm 2W resistor to increase my wattage allowance. I used 14awg stranded power cord wire for my current measurements but the connections were made with just alligator clips. I recharged the batteries between each series of measurements all taken in the same order so although the voltage and current numbers don’t coincide, they do correlate. Using 3 XML LEDs in series powered by a 12V(9s4p nimh 4/5 subc) battery pack 12.2V no load and 8 × 7135 on a custom heat sink slaved to an Atmel Tiny13A(DX 7612 w/o 7135’s) with a 78L05 voltage regulator I took the following measurements:
With .5 ohm resistance,
Low .128A_v resistors 65mV_v emitters 7.36V_v driver 4.56V_v battery(loaded) 11.99V
Med .763A_v resistors 391mV_v emitters 7.85V_v driver 3.28V_v battery 11.48
High 2.6A_v resistors 1.26V_v emitters 9.11V_v driver 100.03mV_v battery 10.12V(recovered to 11.3 )
With no resistors (drum roll please), went to sleep and charge battery overnight…
Low .148A_v emitters 7.32V_v driver 4.82V_v battery 12.15V 21C at sink
Med .875A_v emitters 7.86V_v driver 3.85V_v battery 11.61V 24C
High 2.78A_v emitters 9.18V_v driver1.48V_v battery 10.55V(recovered to 11.84V) stable at 37C
When I put the thermocouple on one of the led sinks the temp did not stabilize before 70C at which point I terminated the test.
I think this calls for a BooYah! For any one that skipped the middle of this post I succeeded in running 3 XML’s in series with modes from a 12V supply to a maximum ~2.8A

Three Tanna leaves to give him life, nine to give him movement. But what if he eats the whole bag?

Scott

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Congrats on finally making this works! I just wish I could understand what you did. 

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Uses a voltage regulator chip (same size and package as 7135) to protect processor from higher voltage battery.
Uses the forward voltage of the LEDs to protect the 7135 chips from the higher voltage battery.
Good for modding lights that have series batteries( 3C,3D Maglights).
Good for lowering current from remote packs like bike lights or lower current switches
A battery pack with less sag will likely still need a resistor but I did everything in my power to push it. I don’t have any more cells to throw at it.

Three Tanna leaves to give him life, nine to give him movement. But what if he eats the whole bag?

Scott

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nice job! If you still have any energy left, give yourself a pat on the back Smile

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Current eta on the new LDO chip for the 8.4V 2s2p xte mod is Monday. I think I will use my 380mA chips for this one now that I know things work. There will be 8 chips in two sets of four(1.5A) with each set pushing two series Leds so each led will be safely driven at max. The heat sink is ready and the 7612 board is stripped with the traces cut and the excess board cut off. It will look similar to this but with two output wires(black one).
A next logical step might be to see if improved heat sinking would allow this mod with the 7135 chips remaining on the board. I have seen various attempts with potting but none that involve direct soldering to the board.

Three Tanna leaves to give him life, nine to give him movement. But what if he eats the whole bag?

Scott

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The new chips came today. These are very low dropout voltage regulator chips. They do the same thing as the 78L05 in lowering the input voltage to the Atmel Tiny13A to 5V but will operate down to a 2s battery voltage of 5.5V. The max input voltage is 16V so these are not an option for a 4s battery pack. The 78L05 has a dropout voltage of 2V and would only work down to 7V, good enough for >3s but not 2s. I should be able to play with one on Sunday. One disadvantage of the new chips is that they require input and output capacitors so the Mouser order also has some insanely small 0805 caps. More carrot juice please.

Three Tanna leaves to give him life, nine to give him movement. But what if he eats the whole bag?

Scott

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So I open up the box from Mouser and everything’s there, the new low dropout voltage regulator chips, the capacitors…(omg, ever try and solder a piece of coarse salt?). I actually knew how small they were because I sized them to sit end to end across the three pins of the regulator. Anyway, no need to worry about board space.
Skipping over all if the pita soldering the set up is similar to the previous one with these differences: Instead of three XML’s in series there are four XTE chips on a 25 mm quad pcb wired 2s2p. As before there are eight 7135 chips slaved to the modified mcu board but the outputs are split into two groups of 4 chips each. The battery pack is two Keygos 26650 4800mAH(right!) wired 2s. I kept the same set of resistors as before to allow me to ramp up the test to full Vbatt. I first used a 1 ohm 4watt resistor(effective) and everything was fine. I measured the voltage drop across the resistor, each string of emitters, the driver, and the battery under load. I did this at low, medium, and high. I ran this series of tests twice more with a 1/2 ohm resistor and no resistor and as one might expect the emitter voltage increased in each series as the voltage across the resistor dropped. On the last test with no resistor and the driver on high the drop across the 7135’s measured 87mV(no load Vbatt was 7.95V by then) and the only thing getting hot was the LEDs. The highest drop across the driver(mcu+7135’s) was 3.25V on low with 1 ohm resistor. I’d have to conclude that this mod passed with flying colours. The next step will be to take one of my 3A Illumination Supply boards and run this test with the new regulator and the chips left on board. It’s almost 2am so pics of the setup will have to wait.

Three Tanna leaves to give him life, nine to give him movement. But what if he eats the whole bag?

Scott

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It works just fine leaving the 7135 chips on the board. Or , I should say, the second one works just fine. The first one died a fiery death under my iron so I hit the poor defenseless bugger with a hammer. Made ME feel better anyway. As I said, it works just fine using a voltage regulator chip for the mcu and up to 3 LEDs in series with an equal number of Li-ions(4 LEDs if 2s2p). I suppose various combinations like 3s2p or 2s4p using slaves shoul work as well. The main thing I’ve found is that virtually no heat is generated by the driver on low or medium and on high the heat generated by the LEDs far exceeds that generated by the 7135 chips.

Three Tanna leaves to give him life, nine to give him movement. But what if he eats the whole bag?

Scott

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Sweet! You've really come a long way since you started out with this Rufusbduck

Congratulations on the progress Smile

~ Ledsmoke ~

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Rufusbduck wrote:
...(omg, ever try and solder a piece of coarse salt?)...

I cringed a bit seeing this.  I don't even like soldering the 7135s.

Thanks for the great read.

http://wardogsmakingithome.org/index.html

War Dogs, Making it Home - Rescue Dogs for Returning Vets

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Chicago X wrote:

Rufusbduck wrote:
…(omg, ever try and solder a piece of coarse salt?)…

I cringed a bit seeing this.  I don’t even like soldering the 7135s.

Thanks for the great read.


I solder the two caps end to end across the three legs. That puts one across the input and one across the output of the VR chip. Getting them to stay put till I solder them is the biggest pita. I’m thinking of making a cradle to pre install the caps on the pins before the chip goes on the board. The rest of the mod is otherwise pretty easy. I haven’t posted in this thread recently as since this part works, I’m working on the next part which is a battery fuel guage similar in size to a 16mm pcb. Maybe even use it to replace the tailcap switch pcb and show the charge level. I think I understand the circuit well enough. The question is do I A) have boards made and populated(expensive), B) have boards made but populated by me(less expensive, more pita but I can make them for different voltage at no added cost), C) make the boards myself using photoresist on either presensitized(better for small traces) or regular pcb material. Feel free to chuckle if you think I’m in over my head.

Three Tanna leaves to give him life, nine to give him movement. But what if he eats the whole bag?

Scott

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