# 12V LED driver



## Oznog (Aug 13, 2007)

I would like to drive 6x red-orange (Vf=3.6V typ) Luxeon Rebels @ 700mA off of a 12v engine-driven electrical system. Don't ask me why, I'm not trying to build an atomic taillight though.

My other setups would have 3x in series and driven by a Zetex 1360-based buck driver. That driver has a switching limit of 1A. The Vf will only allow 3x in series with a buck off a 12v system.

The Rebel's Vf is so variable (2.31V-3.51V @ 350mA) I don't see putting then in a couple of parallel strings. The heat in the ballast resistors would not be acceptable anyways. Nor could a single Zetex drive it.

Is there a simple part out there that can do a boost? Acutally I'm also worried because being off a vehicle's 12V system it's prone to spikes. Above 21.6V a boost converter wouldn't be able to control it or limit the current and many amps could result. Spikes on a 12v system could certainly go that high, only briefly but still.

Otherwise I may just have to build a dual Zetex driver, was trying to avoid that though.


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## frenzee (Aug 13, 2007)

What current are you trying to drive them at? SandwichShoppe has a buck/boost that will take Vin of up to 20V and Vout of up to 22V, so that might work for you. 

Also, a simple solution might be to split it up into 2X3 series strings driven through an off-the-shelf LM340 or LM317 which has a built-in 1.0A (or 1.5A depending on the mfg) current limiter. It IS a linear regulator though, so it will get pretty hot because it will have to sink approx. 3V x 1A (or 1.5A) W, but it will take care of the voltage spikes and reverse polarity.


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## evan9162 (Aug 13, 2007)

First, i think people overemphasize the Vf range. Honestly, I've seen very few red and red/orange luxeons that deviate from about a 3.0V Vf at their rated current. The red/orange/amber devices are much much more consistent than their white counterparts.

Here's what I would do:

Run 2 strings of 3 in series. You can either run 2 independent regulators, or use a 1/2 ohm balancing resistor on each string. That should be more than sufficient to balance current, as, like I've said, the Vf of the red devices won't deviate that much.

Use an LM317 type setup. Actually, I would suggest using an LMS1585-ADJ - it has the same pinout and use as an LM317, but your total dropout will be about 2V, instead of about 3.5-4 of the '317, so you'll be guaranteed it'll stay in regulation if the voltage sags a bit. In addition, to be safe, I'd add a standard 100V diode (or shottky diode) in series to block reverse transients, as neither the LM317 or the LMS1585 will block reverse voltages. Each LMS1585 should cost about $1.20 each. 

frenzee:
You need to be very careful about using the LM317 current "limit" as a safety device. The LM317 guarantees to be able to supply 1.5A, but there's nothing to say it will successfully limit the current to that. The '317 could actually supply 2.5A in spikes, depending on the conditions. It is absolutely not safe to use that specification as a safety device to limit current. When operating in current mode, you still need to use the proper current limiting resistor for the application.

And the LM317 will NOT stop reverse voltage transients. The datasheet specifically states that when using large output capacitors, a reverse bypass diode should be used when the input voltage is shorted, so the output capacitor does not drain through the device. If the '317 blocked reverse voltages, this would not be necessary.


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## Oznog (Aug 13, 2007)

evan9162 said:


> First, i think people overemphasize the Vf range. Honestly, I've seen very few red and red/orange luxeons that deviate from about a 3.0V Vf at their rated current. The red/orange/amber devices are much much more consistent than their white counterparts.
> 
> Here's what I would do:
> 
> ...



Nope. My tests show Luxeon Rebel red-orange 0050 have VERY inconsistent Vf matching, not counting the dV/dTemp. OK my testing was not as well controlled as some but it was a real siginificant difference. Since 700mA is already pretty much the max output for long life, poor regulation is asking for trouble. Especially since the difficult mounting means we're not going to test a bunch of parts for Vf @ 700mA and try to mix and match to make up strings of 3x with a standard Vf.

Linear regs are right out anyways. That's a 12V vehicle system, so Vin can be 14.6v. That would mean dissipating 2.66W per 3x leg and that's not going to be acceptable. Available space for driver and the enclosure itself isn't going to deal with large heatsinks and high heat.


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## Oznog (Aug 14, 2007)

frenzee said:


> What current are you trying to drive them at? SandwichShoppe has a buck/boost that will take Vin of up to 20V and Vout of up to 22V, so that might work for you.



Now that looks handy. Any further info on it? By "20V max", I wonder what the absolute max is? Vehicle systems don't go above 14.6v or so normally, but the starter and other junk can cause spikes that take it well over 20V, just really briefly.

Any idea what IC is on there? They blanked out the label. I could look up its spec sheet if I knew.


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## frenzee (Aug 14, 2007)

Oznog said:


> Any idea what IC is on there? They blanked out the label. I could look up its spec sheet if I knew.


 
No idea (and my guess is it won't provide the full spec current at the maximum Vout), so you better ask for a performance chart first. On the other hand National has a lot of boost converters, e.g. the LM2733, but they all need an external inductor.

Evan, thank for the clarificaiton. I learn something new every day.


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## SemiMan (Aug 14, 2007)

Generally for automotive you are designing for about a 9-16V input range...all the way from dead battery up to a high output regulator on the alternator. Fault conditions are up to 19-20V for failed regulator and 24V for double battery. However, load dump will put 40-60V (depends on the MFR) for limited periods of time .. milliseconds.

Some things you should do:

- Add a reverse bias diode to get rid of negative spikes. Basically a diode in series. Yes you are going to lose some voltage, but it works

- Design for an input range of 9-19V to cover just about all conditions

- Use a zener or some other device to limit the voltage spikes, i.e. you could clamp just 19V


Some other thoughts:

- Consider not running the Rebels at 700mA. When you look at the output versus temperature (which takes into account even short term heating) you will probably find that the maximum light output is at a lower current.

- That may bring you into an issue of 6 LED not having enough forward voltage for a boost in all cases. At 700mA you may be ok...at say 400-500mA you may not. What about having more LEDS at less current? You would use less power and have more light.

There are likely lots of boost chips out there that will meet your needs but not sure about off the shelf products. You may be able to get an eval board from a semi supplier and modify it.

Semiman


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## Changchung (Aug 31, 2007)

Check this out...

http://www.besthongkong.com/index.php?cPath=19_51

I use those drivers for my cars proyects...


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## hank (Oct 19, 2007)

Are those any protection against the range of spikes predictable from an automobile battery, and ok at the usual 13-something volts?

I recall some site that sells a driver specifically for automobile use to protect LEDs from the whole range of troubles, but can't recall (oh, why lie about it, can't even recall what to put into Google) exactly who right now.


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## coolwaters (Oct 19, 2007)

get this. 
http://www.kaidomain.com/WEBUI/ProductDetail.aspx?TranID=2982

im planning to use it to replace my break and tail lights with red and white LEDS.


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## romulus (Dec 7, 2008)

Luxeon Rebels in warm colors are sturdy, and can take spikes, but if you're concerned, get a low pass filter (similar to that of audio applications) just make sure it can handle the current.

There is also a company that makes all kinds of LED controllers. The guy custom-built me a solid state switch with an on-board low pass filter (spike eliminator) for dirt cheap, still works after two years.

Hit this link: http://www.ledhot.com/highpowerleddrivers/1224vsolidstateswitch.html


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## Oznog (Dec 7, 2008)

Way to resurrect a dead thread...

I wasn't aware that Rebels had any unusual "spike" tolerance- what are you basing this on?

We weren't really even talking about the LED's ability to handle spikes, but the _driver_. The thing is that not all driver chips are good for high voltages, and external MOSFETs will conduct through their inherent forward-zener breakdown mode which can make a dangerously high shoot-through current. We could select a higher voltage MOSFET but that generally results in inferior properties like rds-on along with higher cost.

Well not sure what you're calling a "lowpass filter". Large input caps are nice but that's not really what I'd call a "lowpass filter". 

It's very handy to use transorbs to clamp the input. There is a possibility that it'll pull enough current to blow the fuse, but fairly unlikely. Honestly parts with 35V ratings "usually" work on 12V systems for a long time anyways. A 35V part will often be able to sustain significantly higher voltage transients for at least a few milliseconds without a big lifespan reduction issue issue. And transients are probably way different for different vehicles and even very different for locations within the same vehicle.


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## mds82 (Dec 8, 2008)

I would recomend using a 3023-d-n-1000 buckpuck. 2 parallel rows of 3 LED's in series.  It'll work perfect


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## romulus (Dec 9, 2008)

I got ahold of 4 samples of this series of Crees for eval before they were mass produced. I played with them for a few months on an off. I'm not an expert - just sharing my experience.

The filter I'm using is an LC filter coming off 12V, kills inductive spikes well *for my application*. The Driver is PWM, and is setup for constant current, I'm driving 7.25A. The module is 3" x 4" and runs cool. I design high power LED lighting fixtures and drivers for a living, and like I said, I don't consider myself an expert - always learning.


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## snarfer (Dec 10, 2008)

> The guy custom-built me a solid state switch with an on-board...





> I design high power LED lighting fixtures and drivers for a living


So which is it? If you design drivers for a living why would you have "the guy" build them for you?


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## romulus (Dec 10, 2008)

I was chasing this noise problem and I he did alot of stuff for boats, limos, and such so I got some advise. At some point, I just asked 
him to build it and weather-proof it, so he did (for a nominal fee)

I didn't have as much time then as I do now. Now I spend about 10hrs a week tinkering. So there you go....
No, seriously, there you go...


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## SemiMan (Dec 14, 2008)

Well you will resurrect an old thread WHEN YOU ARE OBVIOUSLY TRYING TO SELL SOMETHING!

Sorry, but $55.75 for a 5amp continuous, 10A peak high side switch strikes me as on the high side... considering there are not specifications such as:

- On resistance
- Reverse protection
- Over-voltage protection
- Etc.

This is not really appropriate for automotive as described. One good load dump and that would be all she wrote...unless there are hidden specs not described...

Semiman


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## romulus (Dec 21, 2008)

Hey SemiMan, LEDHOT is a hobbit. I've known him since elementary school, and it took an act of God for him to let me do his website a few years ago. I asked what he thought of maybe getting onto a blog and of course he was hesitant, but said ok. Although I now live in NYC and he is on Long Island we maintain contact. We both started in the LED industry about 22 yrs. ago and his advice still comes in handy. So if there's the implication of selling going on, it's my fault entirely....


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## shortstack (Dec 21, 2008)

look here http://www.instructables.com/id/Super-simple-high-power-LED-driver/ you can make your own for under about $1.50 for each driver.


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## romulus (Dec 22, 2008)

Hey Shortstack,

Absolutely a great place to start - depending on the project. You'll notice alot of folks talking about buck pucks, they're much more compact and efficient, but the cost is also increased. Good post.


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