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Thread: High current (SST-90) driver

  1. #1
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    Default High current (SST-90) driver

    Hi everyone,

    I have been ghosting this board for quite a while, and learning a lot, for which I am grateful. I finally think I may have something to contribute.

    There seems to be a shortage of high current drivers for the newest high power LEDs. As a result of a recent conversation, I have designed a driver capable of up to 10A. I'm an engineer by profession and have built several LED drivers, but in the area of flashlights I'm a hobbyist. Since I don't need this driver myself, the question of whether it's worth building is more a question of whether folks would use it than whether I could make money. I'm posting now to see whether people would be interested in this driver if I built a few of them.

    The characteristics would be:
    Max current:10 A (or less if desired)
    Max input voltage: 12V (16V available at higher cost).
    Dual-level output: Selectable high/low output, via SPDT switch
    Adjustable output: "high" output adjustable from 1A to 10A and "low" output adjustable from 1A to 2.5A by adding series resistors, 10A/2.5A with no resistors.
    Size: 1.0 inch diameter by 0.35 inch thick
    Heatsink: This is a linear regulator, so it will require heatsinking to protect from overheating. Connection to heatsink would be by one screw, #4, #6, 2.5mm or 3mm, or by thermal epoxy. Heatsink compound recommended if using screw.

    This would be a 0-mode driver, meaning it's on whenever you apply power. There's no 'clicky' switch interface. The High/Low switch could have a center off position if you want to turn it off that way. The switch is low current, so it could be a miniature or subminiature switch, not necessary to handle the output current. The driver would be compatible with PWM boards I have seen.

    This driver was originally intended for driving a single SST-90 at 7A from a 4-cell Ni-MH battery pack. Though it could be use over a wide range, it would be most efficient when the input voltage is 0.4 to 1.0 volts above the output voltage. With proper heatsinking , the driver could handle up to 30W dissipation, up to 100 watts output. Higher power levels could be made available if necessary.

    If there's enough interest, I will make some of these, available at around cost, in the appropriate B/S/T area. If not, then I'm sorry to bother you.

    D

  2. #2
    Flashaholic The Dane's Avatar
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    Default Re: High current (SST-90) driver

    As of now demand is high and supply is nill, so work on mate

    Be aware that another similar project is ongoing and ahead of you by sector_cleared

    Dont go spoiling a perfectly good thread with too many facts.
    Henrik
    Creator of The Axe and the BigM*g and i'm sure more silly projects will follow

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    Flashaholic SUBjohan's Avatar
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    Default Re: High current (SST-90) driver

    Actualy there is antoher one in progress:
    By FPPF

    I am verry intrested in a driver wich allows me to driver 2 SST90's in series from a 4 series Li-Ion pack (nominal 14,8V max 16,8V).

    For me dimming should be ideal via a potentio meter.

    Greetz Johan

  4. #4

    Default Re: High current (SST-90) driver

    Interested! I can't contact you via PM. Can you email me sku@expandku.com

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    Default Re: High current (SST-90) driver

    Quote Originally Posted by DIWdiver View Post
    "I will make some of these, available at around cost..."

    D
    Appoximately how much would that be?

  6. #6

    Default Re: High current (SST-90) driver

    Theres a market for a 10A and a 5A if the price is right....

  7. #7

    Default Re: High current (SST-90) driver

    mhh, i linear regulator for a single sst-90 with a maximum input voltage at 12 volts? are you shure?

    my calculations: the sst-90 have 4.0 volts forward voltage at 10 amps, so the regulator must must destroy 8 volts at 10 amps = 80 watt?!?

    if you have 4 eneloops then they have 4.8 volt under load maybe a little less. 0.8 x 10 amps = 8 watt also to much for a portable flashlight.

    just my two cents...

    markus

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    Flashaholic* Aircraft800's Avatar
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    Default Re: High current (SST-90) driver

    Besides the other drivers in design now (mentioned above), I would be definitely be picking one of these linear regulators up. I have a 4 NiMh project already to go, but never finished it because of all the low resistance mods I did would the LED at full charge. I just didn't want to risk it with a $50 LED.

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    Default Re: High current (SST-90) driver

    Quote Originally Posted by mash.m View Post
    mhh, i linear regulator for a single sst-90 with a maximum input voltage at 12 volts? are you shure?

    my calculations: the sst-90 have 4.0 volts forward voltage at 10 amps, so the regulator must must destroy 8 volts at 10 amps = 80 watt?!?

    if you have 4 eneloops then they have 4.8 volt under load maybe a little less. 0.8 x 10 amps = 8 watt also to much for a portable flashlight.

    just my two cents...

    markus
    Hi markus,

    More or less, you are correct. The SST-90 all by itself is far to much heat for a hand held "flashlight" for regular use. The SST-90 already draws something like 4V x 10 A = 40 watts, so far above the more practical 15 - 20 watts max for heat generation.

    With a linear regulator adding 10 Watts of heat per volt of battery voltage above the LED Vf, this adds up fast.

    The 4 - 5 NiMH cells might be a practical use of this linear approach, but even 2 x Li type cells would force the user to wear gloves just with the driver's heat.

    As a practical matter, a quality, efficient, reliable, inductor based current mode driver will have a hard time coming to market for much under $75-100 in hobby quantities, at least based on my simple spreadsheet of parts list and pricing. Anyone wanting to play with SST-90s with other than direct drive or resistor limiting for under $ 30 - 40 worth of even a crude driver will have few other options, at least IMHO.
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    Default Re: High current (SST-90) driver

    I would pay 70 bucks for a good one.

    If you build it, they will come.

  11. #11
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    Default Re: High current (SST-90) driver

    Quote Originally Posted by Sun View Post
    I would pay 70 bucks for a good one.

    If you build it, they will come.

  12. #12
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    Default Re: High current (SST-90) driver

    Quote Originally Posted by Sun View Post
    I would pay 70 bucks for a good one.

    If you build it, they will come.
    At $70, I would make a killing (which would be cool, but is not my goal). They will be a lot less than that. I'm about ready to order prototype boards and parts.

    Can you define good? I expect these will provide full current down to about 4.0V input, 3.6V output. They won't be well protected against surges, transients, ESD, or reverse battery voltage, so they won't be good for automotive applications (intended for battery applications) and could fail with careless handling, but should be pretty rugged once installed in a system. With sufficient heatsinking, they should survive shorted output for any duration.

    D

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    Default Re: High current (SST-90) driver

    Quote Originally Posted by SUBjohan View Post
    Actualy there is antoher one in progress:
    By FPPF

    I am verry intrested in a driver wich allows me to driver 2 SST90's in series from a 4 series Li-Ion pack (nominal 14,8V max 16,8V).

    For me dimming should be ideal via a potentio meter.

    Greetz Johan
    4s Li-Ion would be a lot of extra voltage for a linear driver, all of which would be wasted as heat. For that pack you'd be better off with one of the swithching drivers under development by other members.

    For two LEDs in series. a 7s NiMH or 3s LiIon pack would be better with a linear driver. Even a 2s LiIon would be okay (and much more efficient), if it were acceptable that light output would begin to drop near end of battery life.

    Dimming with a potentiometer would work well with my driver. 500K audio taper would be best, I think.

    D

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    Default Re: High current (SST-90) driver

    Quote Originally Posted by KuKu427 View Post
    Interested! I can't contact you via PM...
    I'm not sure why you can't PM me. I can't log into PM area either. Is that something that gets approved after you turn out to be a good member? I didn't see anything that suggested that in the rules.

  15. #15
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    Default Re: High current (SST-90) driver

    Good for me would mean adjustable in some way thru the range, 5 to 12V input, high efficiency, setup/recall power up,& pwm input.

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    Default Re: High current (SST-90) driver

    Quote Originally Posted by DIWdiver View Post
    I'm not sure why you can't PM me. I can't log into PM area either. Is that something that gets approved after you turn out to be a good member? I didn't see anything that suggested that in the rules.
    Hi DIWdiver, I think you are right about there being some minimum number of posts / time for PMs to work.

    Your idea is good for what it is, a linear driver. It will take some education for people to understand what this means, and the importance of balancing the input voltage, LED Vf, and thermal management. I routinely use resistors to manage LEDs (as well as more advanced drivers) but I understand the trade off. Sometimes, a resistor really is a good way to go.

    Possibly a good place to start is to tell them to limit the battery voltage to no more than 2 volts higher than the LED Vf. I can just imagine someone attempting to use a 12 volt battery voltage with an LED with 4 Volts Vf, and then complaining about run time and heat generation at 10 amps.

    Good luck with your project and please keep us updated.

    BTW - this would be a good thread to have in the "electronics and battery" section, along with with several other current regulation circuits threads in this section. Perhaps a mod will consider this?
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    Flashaholic The Dane's Avatar
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    Default Re: High current (SST-90) driver

    A boost driver would be nice
    Driven by a single LiFePO4 cell that can deliver lots of current


    http://www.batteryspace.com/lifepo44...arate32wh.aspx
    Dont go spoiling a perfectly good thread with too many facts.
    Henrik
    Creator of The Axe and the BigM*g and i'm sure more silly projects will follow

  18. #18
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    Default Re: High current (SST-90) driver

    Quote Originally Posted by Sun View Post
    Good for me would mean adjustable in some way thru the range, 5 to 12V input, high efficiency, setup/recall power up,& pwm input.
    Unfortunately, "High efficiency, 12V input", and "one LED, linear driver" are mutually exclusive.

    Being a linear driver means that the input and output current are the same. The input voltage is dropped across a lossy element (like a resistor) to reach the desired current. A linear driver differs from a resistor in that the lossy element (a transistor) is constantly adjusted to keep the current constant. In a resistor, the value is fixed, so the current changes with input voltage changes.

    To calculate the efficiency of a linear driver is very simple, and the equation will reveal a serious drawback of this type of driver:

    Eff = Vout/Vin

    From this you can easily see that the efficiency tanks as the input voltage goes up.

    However, if you carefully match the input and output voltages, the efficiency can be quite good. For example, this driver was intended to be run at Vin of 4.0-4.8V and Vout of 3.6V (that's a 4-cell NiMH pack running one SST-90 at 9A). When the battery is fully charged, the efficiency is

    Eff = 3.6/4.8 = 0.75, or 75%

    That's not great, but not terrible. But watch what happens as the battery voltage falls. The efficiency rises to

    Eff = 3.6/4.0 = 0.9, or 90%

    On average, you'd expect something in the low 80's for percent efficiency. That's pretty respectable for a simple driver like this. But if you were to use 2 LiIon cells, efficiency would range from 43% to 49%. Not many users would be happy with that! In that case you'd really want a switching driver like some others are working on. With those you'd expect efficiencies of 85% and higher all the time. However those are more complex and likely more expensive.

    As far as your other desires, there isn't anything to set up in this driver. There is a toggle switch input to turn on high or low setting. Settings can be adjusted down with an external resistor. A PWM input could be implemented, but I didn't include that. I could tell you how to do it externally if needed.

    D

  19. #19
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    Default Re: High current (SST-90) driver

    Quote Originally Posted by The Dane View Post
    A boost driver would be nice
    Driven by a single LiFePO4 cell that can deliver lots of current
    Yeah, that would be nice. Maybe in a while, if nobody else does it, and if my experience with this one is happy. However you'd need two LEDs in series to use a boost convertor off LiIon (because the output can never be less than the input voltage). Otherwise it would need to be buck-boost, which is more complex and less efficient.

    You could boost off one or two NiMH cells...

    D

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    Default Re: High current (SST-90) driver

    Quote Originally Posted by DIWdiver View Post
    I'm not sure why you can't PM me. I can't log into PM area either. Is that something that gets approved after you turn out to be a good member? I didn't see anything that suggested that in the rules.

    PM now works.

    D

  21. #21
    Flashaholic The Dane's Avatar
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    Default Re: High current (SST-90) driver

    Quote Originally Posted by DIWdiver View Post
    Yeah, that would be nice. Maybe in a while, if nobody else does it, and if my experience with this one is happy. However you'd need two LEDs in series to use a boost convertor off LiIon (because the output can never be less than the input voltage). Otherwise it would need to be buck-boost, which is more complex and less efficient.

    You could boost off one or two NiMH cells...

    D
    A LiFe is only 3.3V and directly from the charger never more than 3.7V at rest. So under discharge the boost ville be from 3.3V to 3.7V and by the time 11A are used the cell will sag to @3.2V.
    No problemo
    Dont go spoiling a perfectly good thread with too many facts.
    Henrik
    Creator of The Axe and the BigM*g and i'm sure more silly projects will follow

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    Default Re: High current (SST-90) driver

    simple linear regulator, two modes (I'd prefer low / high) sounds good.

    simple reliable and accessable alternative to people running DD could fit a niche

    If losses are low enough, possible secondary application would be for those running from 3xnimh, basically introducing low mode. (though this could be an expensive alternative to a 3way switch and resistor.)
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    Default Re: High current (SST-90) driver

    Wanted to pipe in and say I think the low setting should be about 3.2-4.2 amps. I have built two 3D Mag mods using both the SST-50 and the SST-90 emitters. I have found that 4.2 amps is a good compromise taking heat and output into consideration. In a 3D Mag running both these emitters at 4.2 amps you can still tolerate the hand temperature after an hour run. 75%-80% efficiency would be great. The perfect SST-90 driver IMO would be a 2 mode with a low setting of 4.0-4.2 amps and a high setting of 9.0 amps driven by 5 -12 volts. You could also make two circuits. One 5 - 9 volts for flashlight builds and a 12 volt model.

    On a side note I have noticed that at 4.2 amps and all other factors being equal the hot spot of my SST-50 build although smaller is slightly brighter than my SST-90 build? Now the SST-90 does seem to put out more overall light. Its hotspot is almost twice as large as the SST-50's at 4.2 amps. I am also sure at higher currents the SST-90 would spank the SST-50. The SST-90 has much more spill.

    Great thread can not wait to see how it develops!

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    Default Re: High current (SST-90) driver

    3.2A is low? wow.
    While OP said adjustable, I do like the reference 1A, something almost useable for physical tasks, like tying your boot, while you're out looking for whatever 9A is used for.
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    Default Re: High current (SST-90) driver

    Hi all,

    Parts should be here for prototype build over the weekend. I'm picking up a borrowed 20A power supply tomorrow for testing. I'm probably more excited than any of you!

    At the moment I'm thinking of offering it in 4 versions. Hi/Lo settings would be:
    5A/1.25A
    5A/5A
    10A/2.5A
    10A/10A

    The reason for offering high and low modes the same is that then the user can pick his own low mode by simply adding a resistor to one of the switch terminals. Note that the switch and external resistor are very low current.

    If there's some consensus on a setup other than those 4, I might offer that instead or in addition.

    I expect the driver to regulate nicely and predictably down to about 10% of the max setting (5 or 10A). Somewhere below that the behavior would get flaky.

    D

  26. #26
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    Default Re: High current (SST-90) driver

    Is there a way to have the output adjustable by resistor change on the board? I also am leaning toward running the ssr-90 at 4.2A.

  27. #27

    Default Re: High current (SST-90) driver

    Quote Originally Posted by DIWdiver View Post
    Hi all,

    Parts should be here for prototype build over the weekend. I'm picking up a borrowed 20A power supply tomorrow for testing. I'm probably more excited than any of you!

    At the moment I'm thinking of offering it in 4 versions. Hi/Lo settings would be:
    5A/1.25A
    5A/5A
    10A/2.5A
    10A/10A

    The reason for offering high and low modes the same is that then the user can pick his own low mode by simply adding a resistor to one of the switch terminals. Note that the switch and external resistor are very low current.

    If there's some consensus on a setup other than those 4, I might offer that instead or in addition.

    I expect the driver to regulate nicely and predictably down to about 10% of the max setting (5 or 10A). Somewhere below that the behavior would get flaky.

    D
    10A and 5A... would allow driver to work with SST-50 and SST-90

  28. #28
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    Default Re: High current (SST-90) driver

    Quote Originally Posted by Sun View Post
    Is there a way to have the output adjustable by resistor change on the board? I also am leaning toward running the ssr-90 at 4.2A.
    Yes, you could change a resistor on the board. The one that's large and easy to change is readily available in only a few values, which would give max currents of 10, 8, 6.7, 5, 4, 2.9 and 2.5A (I could go lower but that would be silly - who wants such a puny light?).

    There are two other resistors, one for high and one for low, that can be used to set the current anywhere below the max value. Unfortunately, these two are tiny - only 0.06" x 0.03", so you have to have good eyes and good hands.

    Info will be available with the boards.

    D

  29. #29
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    Default Re: High current (SST-90) driver

    So I tested the prototype yesterday. It works pretty well. I ran it for a while at 6V input, 3.6V output, 10A. It seemed to handle that okay.

    There are two problems, both easily solved:

    I was in a hurry to order the boards so they'd be here for the weekend, and didn't notice that the copper areas didn't fill, so several high-current connections were missing. That was easily solved with some foil and wire. I'll make sure the next boards are right!

    To keep the price low, I spec'd a FET that seemed adequate, but not overkill. In practice, it's a bit wimpy. That's always a problem with FETs - the specs say what it will do in ideal laboratory conditions, and you have to figure out how much worse they will be in real life. This one wouldn't give the full 10A at less than 4.7V input, and I melted two of them by pushing the power dissipation too high. It also doesn't seem to transfer heat to the heatsink very well. Tomorrow I'll order some beefier FETs and I should be testing again at the end of the week.





    As you can see, the tab of the transistor is between the board and the heatsink. This allows direct contact to the heatsink, while a single screw secures the board and the transistor; it also raises the board off the heatsink a little. This gives room for the components to be on the back of the board, and allows the wires to stick through the board a little.

    The prototype board is square (because it's cheaper that way). The final board will be round. You can see the circle that will eventually be the board edge.

    The large potentiometer that is mounted on the heatsink is a current control. I happened to have a 1 Megohm pot available, and it adjusts the current from 10A down to 0.6A. A 500K pot would get you down to 1.1A and give better resolution at the high end.

  30. #30
    Flashaholic* Aircraft800's Avatar
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    Default Re: High current (SST-90) driver

    Nice to see progress so quickly! Thanks for the update!

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