Power for LEDs from 12.6 VDC (automobiles)

[kinarfi]

I've been playing with LEDs for my off highway vehicle and I think I have come up with a very viable power supply so you can drive as many LEDs as you want with them ALL in series(with in reason). It involves boosting the voltage a little above what is needed and regulating the current through all of the LEDs with one LM317. I haven't built the final prototype yet, but from what I have built, I'm sure it will work, I plan to drive 4 10 watt, 12.6V high output LEDs in series and another set of 26 3.2v 20 ma bright white 5mm LEDs. Generally, you can only put 3 or 4 of these in series and have to regulate the current of each set, this way you can probably run 20 or 30 in series. By setting the voltage just over what you need, the LM317 has enough head room to work with out generating a bunch of heat.
Feed back Welcome and suggestions welcome, I haven't determined what size caps should be used yet nor have I determined the correct diodes, however, I do know that they need to be high power and probably heat sinked.
Enjoy LED Folk,
Kinarfi

 

[ronsimpson]

Too many parts.
Because you have LT spice; Look at the LT3465. It boosts up and regulates current in one step. No need for a linear regulator. It can only handle 16 volts input which is a little too low for automotive. But the idea of boost up and regulate in one step is the point. (no diodes, no FETS)

Also look at LTC3783 for a larger version. These files are in your LT spice. In seconds you can have it running on the PC.

 

[kinarfi]

Thanks for your input ronsimpson, I updated my spice and looked at the .asc for LTC3783 and added a few more LEDs and I may have done it wrong, but it didn't seem to work with the extra load. I also eliminated a few parts from my design and changed it some, but it seems to work and I don't think I have found the limits yet. My original design was to drive several 800ma 12.6 volt 10 watt LEDs on my vehicle and I found that the difference between battery voltage and alternator voltage would destroy them, so I had to come up with a current regulator that didn't care what the voltage was. I think this may work. If you or anyone else have some suggestions, I'm listening!
Thanks Again,
Kinarfi

 

[ronsimpson]

The LTC3783 regulates current by looking at the FBP pin.
It also shuts down if the voltage is too high. This done by OVFB. You might want to change the resistors in this pin.

 

[kinarfi]

Hi Ron,
I've been playing with the LTC3783 on Spice and have not been successful. My 4 10watt LEDs run at 800-900ma and have a voltage drop of ~12.5 - 13.5 and I'm trying to put them in series, so I'm trying to run the 3783 in constant current mode, but can't seem to get to the 800 ma mark or above the 55 volt mark. Would mind giving me a hand with designing this thing, Please?

Also, I recently got a LCR Multimeter and of course, started playing with it, mostly measuring the inductors I have salvaged. An interesting thing I noticed on one inductor that had 3 separate windings, each of 29uh were still 29uh when paralleled, but when seriesed, I measured close to 300uh. I think I understand the paralleled winding staying at 29, that would be the same number of turns, but equal to having a larger diameter wire, but the seriesed turns appears to be multiplied by 3 squared.
Do inductors on the same core act the same a inductors individually wound in series and parallel

 

[kinarfi]

UPDATE - - - It appears to by my IRF2805 that was limiting everything on spice. Tried another FET and every thing changed, going to go play with spice for a while, again.

 

[ronsimpson]

Inductance is related to turns squared. Three windings in series will have 9 time the inductance. (on the same core)

 

[ronsimpson]

Things that may be wrong with your circuit.
Vin=14.4 volts at 3.8A ....R6 may be too large. It limits the current from Vin.
Vout may be too high. R7/R8 will shutdown the IC if vout is too high.
Read the data sheet and see what voltages should be on these two pins.

 

[kinarfi]

Thanks for your help Ron, I decided to call Linear and ask them a question and if there were later and greater devices for what I was trying to do, they said the LTC3783 was good but about 9 yrs old and that the ltc3787 was newer and better and higher voltage. They also said the lt3756-2 would be good for my 18.5 V, 3 amp Computer power, So I ordered some samples. I'll update when I get things done.
Thanks again,
Kinarfi

 

[kinarfi]

hey Ron, not so sure I want to say thanks after all I bought 3 of those LTC3783 and they got here today and I went to work making a circuit, but they are sooooooo small and the leads so delicate that I never got to put power on to try them, I couldn't even get the attached to the circuit board. I guess if you're going to use these devices, you need to get the $125 demo board or have circuit boards built for them, being a thru hole type person, all they did was cost money and frustrate me, after I a few wires hooked up and I tried to do another, I just managed to undo some of what I had already done. Probably are real nice circuit, but not for john Q public. Working on another method to accomplish my task. So far, here's where I'm at, got any suggestions? Haven't really tried it, but I have the oscillator running and using 600 v 20 amp fet. Need to figure out the right size inductor to use.
Kinarfi

 

[kinarfi]

I have this running and seem to be doing an excellent job and it was made with salvaged parts and pieces, mostly, and no elaborate chips. Yes, I'm proud of my contraption, but it's something the non expert can put together to get a higher voltage to drive several LEDs in series. It was driving 2 100 watt incandescent lamps in parallel and having the opamp shutting down the oscillator because the set voltage was being exceeded. This limits the heat in the LM317. scope shot is NFET drain with 1 100 watt incandescent lamp drawing 600 ma at 65 volts with ~ 13.0 volts in.
Kinarfi

 

[kinarfi]

Too many parts.
Because you have LT spice; Look at the LT3465. It boosts up and regulates current in one step. No need for a linear regulator. It can only handle 16 volts input which is a little too low for automotive. But the idea of boost up and regulate in one step is the point. (no diodes, no FETS)

Also look at LTC3783 for a larger version. These files are in your LT spice. In seconds you can have it running on the PC.

I'm still looking for an easy to use SMPS up the voltage in my off road vehicle to drive some LEDs. Just found a L296 in my inventory of stuff and was wondering if any one know of anything better. The L296 is a buck device that can be used as a boost device. The LTC3783 would have been perfect if it was so small physically, I ruined 3 of them by breaking leads off while trying to attach wires to them.
Any way what I'm looking for is through hole device similar to the LTC3783, any suggestions?
Thanks,
Kinarfi

 

[KJ6EAD]

You need to know about SMD breakout/adapter boards.

http://www.dipmicro.com/store/PCB-SOIC-SSOP16
http://www.adapt-plus.com/products/adapters/prod_smt_board.html
**broken link removed**
http://cimarrontechnology.com/surfacemountadapters.aspx
http://www.logicalsys.com/smt-to-thru-hole-adapters.asp
**broken link removed**
http://www.capitaladvanced.com/products.htm

Be sure to choose one with a hole or land extension to acommodate soldering of the pin 17 heat slug of the LTC3783.

 

[kinarfi]

Yes, I definitely needed to know about them, and now I do. Book marked this page
Thank You Very Much
Kinarfi

 

[kinarfi]

Update, quoted from my post in general electronics chat, Update, after building several boost circuits with the 555 timer, I have come up with a few ideas that need to be bounced off of others, Please take a look at the following attached drawing and see if you can find errors and add comments if needed.
It is drawn to represent installation on a Vector 8022 board which has the "P" pattern or the traces running end to end. The breaks in the lines represent where the traces need to be broken. This makes for a board that is about 1" x 2".
Thanks,
Kinarfi
I did try using a couple of the above mentioned surf boards and ended up soldering the leads together and busting them off and never got even one to work. My favorite device so far by far is the Linear Technology LT1270A, simple and powerful, and about $10.00 USD. This design works well and can be adjusted to even higher power than the LT1270A by the use of higher powered FETs and Diodes.
Thanks,
Kinarfi

 

[Ubergeek63]

I did try using a couple of the above mentioned surf boards and ended up soldering the leads together and busting them off and never got even one to work. My favorite device so far by far is the Linear Technology LT1270A, simple and powerful, and about $10.00 USD. This design works well and can be adjusted to even higher power than the LT1270A by the use of higher powered FETs and Diodes.
Thanks,
Kinarfi

Well there are options that would only run $3 for that much if memory serves...