need help finding/ designing a schematic 3A led driver

[poolman966554]

Hello everyone!
1st post here, and like the forum layout. lots of good info!
A little background, im 31 yrs old, love riding my sportbike, dirtbike, and my quad when work dont get in the way! Ive been 'tinkering' with electronics since i was about 10, that said, i have no real useful circuitry experience, but have 8 yrs in HVAC experience. in that time ive learned how to read (hvac equipment)schematics - pressure switch, and rollout switches, relays etc.. not the usual circuit symbols. But that has slightly changed..

I decided to try and 'build' a 12 xml led light bar for the cost of one. I was told on candlepowerforums(many times) i should use a driver, but insisted that using the $4 in resistors it was worth a shot..(the driver recommended was from Taskled.com - "hyperboost". unfortunately the the sales person said this was not for automotive use, parts too sensitive. I mentioned installing a TVS, he basically said its your $$. the drivers $40 + shipping.

Scenario: FOR STRICTLY OFF-ROAD USE ONLY!! lightbar is attached to a quad for plowing snow, with a winch to raise/ lower plow. This light is required as with plow raised, it covers my headlights. ATV running voltage is 14.4V idle and revved, drops to 12.8V under winch load. I 'think' it has a 15A alternator..
I currently have 3 parallel strings 4 xml's in series, with a .5ohm 10w resistor in each series. Ill add one very patient member from CPF insisted i install a TVS to save leds from winch load dump.
Works fine while bar was in room temps, but outside in 0' weather(non-heated shed), the leds barely pull 1.9A when i where i want 2.7ish..

So, the learning curve of playing with Fv of leds(with extreme temps), resistance and amperage piqued my interest. i have since researched, studied and built a single transistor fm transmitter for my work van(cd player broke) and works great!(works well with (2)18650's i series aswell)
schematic: https://imgur.com/BBljw0U
and just because i found a good deal on a lot of 20 max2606(and i like tinkering), ive purchased all parts x2 to build this just for comparison,
https://imgur.com/bazuoCW

you can see the complexity is pretty low, but i still made a trial run 'super-gluing' single sided clad board to the respective places to connect components,and it worked.
Ive since found the laser toner/iron transfer method, and etched with muriatic acid/ hydrogen peroxide mixture and have had great results with thru-hole components. Many friends are happy lol. Since then ive acquired an old toaster oven,(id like to modify) and would like to try my luck at surface mount components.

So, on the the point.. i wanna ditch the resistors, and build a 3A boost driver for 12 xmls in series. ill even build 2 drivers if 120 watts is to much for a single driver.(even at 95% itll be 6-7W to dissipate)

Heres my problem. I dont know how to "construct" such driver. I can follow a schematic 'sorta' like a road map, but no idea how i can manipulate one..

Ive googled 3A led driver and found many images, but some displays wont drive 3A, cant find parts, or dont display component specs.
Ex: https://www.maximintegrated.com/datas...ex.mvp/id/5876
No component specs listed(honestly i like this as in the specs it says its 10A output, and voltage is in range.)

Ex 2: **broken link removed**
PERFECT except input voltage(and kinda intimidating) Can this be manipulated lower? or is that IC working voltage?

Ive also found things like the LT3477, but all schematics ive seen are only show 1A draw per string..

I was hoping someone here could point me to a simple 14v auto 3A driver schematic, with parts that are easily obtainable from digikey or mouser etc..

Thanks for your time!!

 

[ronv]

A couple of these might do it. Don' think you can build one as cheap.

**broken link removed**

 

[4pyros]

Works fine while bar was in room temps, but outside in 0' weather(non-heated shed), the leds barely pull 1.9A when i where i want 2.7ish..

I don't think this has anything to do with cold resisters.
What is the FV of your LEDs?
What was the battery voltage at the time.

 

[cowboybob]

Welcome, poolman966554!

I get the impression you'de like to build your LED driver circuit rather than buy one (although buying one would be easier and, in the end, probably cheaper, but what's the fun in that?).

If that's the case, I'd check out Linear Technolgy's (LT) stable of boost ICs. LT is very free with detailed schematics (that include component values) and they also give away a free version of the simulator software called LTSpice (very handy).

I've used their products and they're aces...

https://www.linear.com/designtools/software/demo_circuits.php

 

[poolman966554]

I don't think this has anything to do with cold resisters.
What is the FV of your LEDs?
What was the battery voltage at the time.

as the datasheet for xml suggestes, the temp will factor the FV of led. if Fv low, then amperage is low..

I thought about the battery, but i figured the stator would bump voltage back to 14.4 once started.

This is why id like to try constant current regardless to voltage

 

[poolman966554]

Welcome, poolman966554!

I get the impression you'de like to build your LED driver circuit rather than buy one (although buying one would be easier and, in the end, probably cheaper, but what's the fun in that?).

If that's the case, I'd check out Linear Technolgy's (LT) stable of boost ICs. LT is very free with detailed schematics (that include component values) and they also get away a free version of the simulator software called LTSpice (very handy).

I've used their products and they're aces...

https://www.linear.com/designtools/software/demo_circuits.php

SWEET! thanks for the info!! ill check it out!

 

[KeepItSimpleStupid]

A really quick way could use the LM350. See fig 32 here: https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=0CCcQFjAA&url=https://www.ti.com/lit/ds/symlink/lm350-n.pdf&ei=uOfhUq7xCozMsQTYuYLwAg&usg=AFQjCNFUohdOqvNG5OwtnTYGqCCJUjQjuA&sig2=71avnJoR9qPckhHG6XWLZA&bvm=bv.59930103,d.cWc&cad=rja

You need to include about 3V for the regulator when designing. You have to provide heat sink, thermal insulator and a mounting kit. The kit will include screw, dome washer, a nut and a shoulder washer. Sil Pads which are thermal insulators don;t require thermal grease. Mica and Kapton do.

This https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=7&ved=0CFgQFjAG&url=https://www.jos.ac.cn/bdtxbcn/ch/reader/create_pdf.aspx?file_no=10092702&ei=ZujhUt6hJurMsQSdv4LABQ&usg=AFQjCNG3IgKJGclIkMpZ9cUW6oQjIEiEqw&sig2=12RQKdYxLfCWkeP64AXqDg&bvm=bv.59930103,d.cWc&cad=rja link suggests the forward voltage of the LED increases with lower temperature AND there is a wavelength shift.

This would account for your observation. You should measure the voltage drop across a LED at room temp and then outside. Use the value of Vf that you got outside.

So, you'll have to consider worst case power supply, say 10 V and then the number of LED's and the max Vf.


Supply Voltage(worst case) < = (n*vf) - 3 V;

 

[cowboybob]

Taking into account the temperature issue, and KISS' solution for that, many of the LT (and other's) ICs have external output voltage and/or current adjustment inputs. To these you might be able to link, for instance, a thermistor circuit.

 

[KeepItSimpleStupid]

Well, this is 3000 mA which is 3A: **broken link removed**