LED question - understanding data sheet and driver

I’m interested in these Bridgelux LED strips: https://www.digikey.com/product-detail/en/bridgelux/BXEB-L1120Z-35E4000-C-B3/976-1732-ND/7907661

In choosing the correct driver I’m not understanding nominal current and max current.

The data sheet: https://www.bridgelux.com/sites/default/files/resource_media/DS132%20Bridgelux%20EB%20Series%20Gen3%20Data%20Sheet%2020190617%20Rev%20A.pdf

states that the nominal current is 700 mA and typical voltage is 38.3 v. It also lists max current 1400 mA and min and max voltage of 35.6v to 41v. The data sheet also shows some performance charts that suggest running at max current will give max lux %. Obviously at higher heat which reduced both voltage and luminous flux, and I have no idea how much heat would be produced at max current.

The driver I’m looking at is a Constant Current, Voltage, and voltage of 24 - 48 and max current of 10A. and power 480w

I want to wire 10 of these together in parallel, typical voltage would be 38.3 and current would be 7 Amps. My question is what is the max current rating about? 10 of this in parallel would have a max current of 14A, which is outside of the drivers range, is that in issue? Can these LEDs be run at max current continuously (certainly not with this specific driver). If so what are the negative effects of doing so.

Also, this driver allows for 480w, yet my configuration only runs at 7A * 38.3 = 268.1. Would it be better to run these with a lower wattage driver?



“Nominal” drive current values for such things generally indicate the operating conditions under which most of the device’s other characteristics are measured and specified, whereas “maximum” conditions indicate operating conditions beyond which the service life of the unit is likely to be imperiled.

As a general rule, the actual LED dies themselves within their plastic housings would rather be kept at 85°C or lower; if your mounting fixtures and thermal management solution can achieve that when running at max current, it’s usually not a problem, though there may be some shifting of color characteristics, etc. On the flipside, it’s possible to build a crummy thermal solution that’ll have the dies cooking away at 100°C+ when running at only half of nominal, and that would be a problem…

The typical CC/CV led driver forces the listed current out of the output, so long as the connected load produces a voltage within the listed output voltage range; if the load changes so as to present a higher resistance (e.g. all the LEDs burning out) the maximum voltage that will be developed at the output is the upper limit of the listed range, 48v in this case. A “maximum current” in that context typically refers to output current before any dimming control is applied.

Connecting 7 of those strips in parallel to a driver with a 10A output would result in 10/7=1.43A applied to each strip, more or less. Probably a bit on the aggressive side.

Driver power ratings describe a maximum capacity, rather than an operating condition; a 5-gallon bucket can potentially hold five gallons, but it doesn’t necessarily mean there’s that much stuff actually inside. Same sorta concept.

This resource on driver selection might be useful.

Thank you. I read your “driver selection…” article, it was useful.

One thing I’m not understanding about the driver, is the output voltage controlled by the user, via a switch or programatically or something? If not how does the driver determine the voltage in a parallel array. My understanding about how lights work, and electricity in general (and please correct me if I am wrong), is that the load draws (or pulls) the current it needs, but the voltage is set and pushed at the source. Is that correct? If so how does the driver determine what voltage to send to the LED array?

With my chosen LED strips and Driver, if I wire in parallel 14 strips, the driver current output would be 10/14=714mA applied to each strip, probably fine for the nominal current of 700mA, correct? In that configuration what voltage would the driver supply, and is it possible to adjust that voltage?

Lastly, do you think wiring in parallel given the CC/CV driver is a good idea, or would in series be better?

Thanks very much.

It’s a common point of confusion though one which I’ve grown quite familiar over the years, so I would ask your pardon should I come across as abrupt.

Electricity behaves much like a fluid such as water; push on it (voltage) and it flows (current). The relationship between how hard one pushes and how much flow results is resistance. In many devices that relationship is directly proportional, in others such as LEDs it’s nonlinear. LEDs are a bit like one of those uncurling party favors one blows through to make annoying noises to commemorate the completion of an orbit around the sun; you don’t get a lot of flow until you blow hard enough to unfold the thing, at which point you don’t have to blow all that much harder to empty your lungs in 5 seconds than in 20 seconds.

Most LED drivers are designed to deliver a specified amount of current/flow they adapt their output voltage to achieve that goal, though they can only do it properly if the voltage that results from that amount of current flow lands within the specified output voltage range. It’s a bit like riding a bicycle with multiple gears, there’s a certain rate at which it’s comfortable to pedal, depending on terrain. Within that range, all is good, outside, not so much. In this analogy, the bike rider represents the AC line supply, the LED represents the terrain, and the LED driver represents the choice of gear on the bicycle; one picks an appropriate gear to make an acceptable match between the power source and the job to be done.

More directly to your questions, yes, 14 of those LED strips in parallel would give an estimated 714mA through each, though there will be some variability among them due to manufacturing tolerances and the resistance of your chosen interconnect wires. Resulting output voltage from the driver would be whatever it takes to push that 10A through, provided that this number is within the 24-48v range. Else, it will limit at 48v or thereabouts.

Series and parallel arrangements each have their pros and cons; it’s your choice, but given the context of many devices each with a 35v-ish forward voltage, series operation would put you into safety hazard territory with respect to voltage quite quickly, and I’d not recommend it under the circumstances.

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Thanks. Your analogy really makes it more clear.

Just to solidify what you are saying with specifics if I may, and I realize my knowledge is pretty basic so I appreciate your tolerance. Given the led strips at .7A nominal 1.4A max, and 38.3v typical and range of 35.6v to 44.3v, and driver of 10A max and voltage range of 24v to 48v. If I were to wire 10 led strips in parallel that would give 10/10=1A to each strip. In this configuration the voltage supplied by the driver would necessarily be greater than the typical voltage of 38.3v? Let’s say maybe the voltage was somewhere about half way between typical and max at 39.5v. Then the overall power being supplied by the driver (and absorbed by the 10 led strips) would be 10A * 39.5=395 watts. Correct?

With a bit more complicated wiring, say I was using the same model led strips but at half the length. These strips have the same amps, but typical voltage is half or 19.1v and max of 21.6v. Could I take two sets of 10 strips and wire in parallel, and then take those two sets of 10 and wire them together in series. And apply the same driver to them, would that work? My only doubt about it working is that the driver supplies a minimum of 24v and the strips have a max of 21.6v. I know in series the voltage is doubled, but when the current hits that first set of 10 would that be too much voltage?

First off, any LED datasheet worth a sneeze will have a chart something like the below, which describes the relationship between applied voltage and resulting current flow for the device. That image was taken from the 8th page of the pdf datasheet for the part originally referenced. It applies for some specific stated temperature, and describes nominal conditions; slight variations will occur due to variations in manufacturing and differing temperatures. That chart answers questions in the line of “what voltage at what current” or vice-versa.

Yes, assuming your estimation of the Vf at 39.5 is correct.

To a first approximation, this would function identically to the proposed arrangement of 10 parallel full-length strips.

Voltage is always measured across two points; if one is talking about what voltage a given strip “sees,” you measure across that device alone. The output voltage of the driver is measured between its own output leads, so if you have two identical devices/assemblies across that output, the voltage present at the midpoint of the two, measured relative to the driver output, would be half of the total.

Thanks very much.

Ah yes, the datasheet, I guess I should have looked more closely at that information, lol.