Built another DIY led driver!
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Old 10-28-2011, 04:02 AM   #1
O2surplus
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Built another DIY led driver!


I'm experimenting with a teensy-weensy, tiny IC that works as a buck controller for driving high current leds. The chip is the LM3409HV. It can control LED loads up to 75 VDC and 5000 ma of current, so you can see the potential for such an led driver designed around this chip. I recently designed and had a PCB produced for this chip. I still have to adjust some of the component values as the first one tested produced 2700ma with a 27 volt input ( My target was 2000ma). Here's a photo of the first driver. Notice how tiny that little IC is. Its dwarfed by nearly every other component on the board! Let me know what ya'll think.
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Old 10-28-2011, 10:10 AM   #2
doncityz
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The actual driver is that UA7805 IC. The tiny IC is a PWM wave generator only (for switching purposes). Using PWM controller to power up LEDs is a good idea - since efficiency is superb. But, take care of the temperature of that UA7805. Any semiconductor leg will need to be operational at below 90 deg C (im guessing that is the burn point of the PCB - rough guess). And the junction temperature of the internal, well, usually should be aimed to be less than 150 deg C. As for me, when in doubt, slap a heatsink on it, and you're good to go lol...

On a second note, that UA7805 is already heatsinked to the silver track of the pcb. Probably it is enough.. not sure. just follow the circuit rating, you should be ok with it.
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Old 10-28-2011, 02:00 PM   #3
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In it's most basic sense, it is a PWM driver, but it really is a lot more than that. The LM3409HV is an external FET LED driver. Functions just the same as an internal FET driver, like an LM3404 (very common NI driver). The external FET allows much higher current and voltages. The driver IC still has all the smarts for current sensing, frequency adjustment, and fault monitoring.
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Old 10-28-2011, 03:05 PM   #4
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Evilc66

You nailed it right on the head - It's a lot more than just a PWM driver. The combination of a very smart control IC and an appropriately chosen FET, make for a really efficient LED driver. Not that I would, but theoretically, this driver design could drive 5 strings of 18 XPG's @ 1000 mA per string- in a parallel wiring scheme. That's a lot of LEDs for a driver that only costs around $25 to build. Of course my little board would probably melt down trying to drive a load like that, but with proper design and component choices, it is possible.
The UA7805 is a 5 volt regulator that is only included in this particular design to provide power for a Nueventics "Synjet" Led heat sink cooling system. The "Synjet" cooler only pulls about 80mA while in operation, so it's current demands will be very light on the 5 volt reg. In any case, The regulator has plenty of "thermal vias" under it to wick the heat generated by the regulator to the bottom plane of the PCB. The "Synjet" is another "smart" component in the lighting system, as it will respond to the same PWM signal as the LM3409, thus it will speed up or slow down it's operation speed based on the dimming signal from the Led driver dimming controller.
I'll be experimenting with this little driver over the weekend and I'll post my results. If I can get it to behave predictably, I'll post the info so people can create their own.
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Old 10-28-2011, 05:57 PM   #5
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does that mosfet get hot at all?

Maybe a GPU Memory sink ontop will allow it to handle more amperage?

how do you adjust voltage? i dont see a pot?

so im to assume you have to wire up a 75V array?

75 / 3 = 25 LED array?
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Old 10-29-2011, 03:17 AM   #6
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So do you mean, that Q1 is the actual current driver?
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Old 10-29-2011, 04:01 AM   #7
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Quote:
Originally Posted by doncityz View Post
So do you mean, that Q1 is the actual current driver?
Yes-Q1 is a P-channel MOSFET. The MOSFET is responsible for handling the actual current load of the circuit. The "brains" behind it is the LM3409 buck controller( it's the tiny IC with the 10 pins )
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Old 10-29-2011, 05:22 AM   #8
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Quote:
Originally Posted by O2surplus View Post
Yes-Q1 is a P-channel MOSFET. The MOSFET is responsible for handling the actual current load of the circuit. The "brains" behind it is the LM3409 buck controller( it's the tiny IC with the 10 pins )
It looks really small though to able to handle 5 Amps. That's crazy. Does it get too hot to touch at 2700mA?
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Old 10-29-2011, 08:16 PM   #9
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Quote:
Originally Posted by doncityz View Post
It looks really small though to able to handle 5 Amps. That's crazy. Does it get too hot to touch at 2700mA?
I have to admit- I wasn't paying to much attention to the MOSFET when the driver was running. I'm assuming it would get pretty warm too (It's rated for 3.5 amps) but letting the smoke out of a $46 BridgeLux was my main concern. I only ran the driver long enough to get some voltage and current readings, and will try again after I adjust some component values to bring the current down to an in spec level.
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Old 11-30-2011, 03:35 AM   #10
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O2, have you had an opportunity to change your component values? Also, what configuration of synjet are you experimenting with?
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Old 11-30-2011, 04:23 AM   #11
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O2, have you had an opportunity to change your component values? Also, what configuration of synjet are you experimenting with?
Yep, I got it sorted out. I just mailed out 10 of these little guys to a member for his new lighting system. I managed to get the maximum current down to around 2150mA, which is within specs for the LED he'll be using. He'll be using the "Synjets" to cool heat sinks designed specifically for the LEDs he's chosen. I don't want to give away too much info as he's going to do a build thread on this forum, when he's done with the build. It's gonna be a game changer.
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Old 11-30-2011, 04:43 AM   #12
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That sounds promising.
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Old 12-15-2011, 02:46 PM   #13
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Well folks- here's the newest design.It features Analog Maximum Current adjust-ability and PWM dimming. I designed this on to operate off a 48 Vdc supply and output up to 4.5 amps. I'm sure (with the proper fuses and load balanced led strings) this little driver could run 48 XPG's at 1000ma (4 strings x 12 ) or 1 string of 12 XML's at 3000 ma. Not too shabby- IMHO, for a driver that costs around $20 to build. I'll post up the EAGLE files and a BOM if anyone's interested in building their own.
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Old 12-15-2011, 03:02 PM   #14
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I want to build my own, but I'd need handholding throughout the whole process.
I think I'll wait till after I've put my arduino PWM controller together...
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Old 12-15-2011, 03:57 PM   #15
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That is exactly what I need. Amazing.
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