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.
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
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.
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.
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
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 4x4. 2s2p I think is very plausible and 3x3 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).
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.
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.
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.
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.
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.
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 :-)
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.
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
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.
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 x 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
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.
