Wiring CC LED drivers in parallel? - Page 1
Forum section: electronics / projects

author: Artlav
author_rank: Frequent Contributor
timestamp: May 25, 2014, 06:33:53 pm
content: I have a single 80W (38-42V, 2A) LED COB, and i want to drive it from a 48V supply.There aren't that many driver options in this range of voltage and current.Come to think of it, i have found none at all.However, there are up to 56V rated 1A drivers from MeanWell, so i was thinking of wiring two of them in parallel.Conceptually, this should work - they should both be regulating their part of the current, naturally splitting into two.To try it, i got two LDD-700H (http://pl.mouser.com/ProductDetail/Mean-Well/LDD-700H/?qs=erfQA2AIGbXYF3x8KGE0pA==) 700mA CC drivers, and wired teir outputs in parallel, driving the same LED.The LED does get it's 1.4A, but one driver heats up quite a bit more than the other.Trying to connect a third one causes all of them to shut down into some sort of error safe mode with zero output within half a second.Not good.So, main question - can you wire CC LED drivers in parallel somehow, and if yes - how to do it safely?Bonus question - how can you drive an LED like that from 48V? (no, LM350 is too hot to be an option).

author: mariush
author_rank: Super Contributor
timestamp: May 25, 2014, 06:59:11 pm
content: There are linear regulators that can work at up to 60v, for example LM317HVT :http://uk.farnell.com/texas-instruments/lm317hvt-nopb/ic-v-reg-linear-adj/dp/1469086Read the datasheet, it shows some circuits that allow you do make a constant current power supply with it, you'd just have to change the external transistor to one that handles up to 48v or whatever you want.LM317HVT can only do 1.5A but you can pair two of them to do more current, or you can use the external transistors to do the "heavy lifting" so one lm317hv will be enough.

author: Artlav
author_rank: Frequent Contributor
timestamp: May 25, 2014, 07:13:40 pm
content: Quote from: mariush on May 25, 2014, 06:59:11 pmAFAIK, you don't need a high voltage rated linear regulator to do constant current.Just put a floating one with suitable current rating across a current sense resistor.I had been driving a similar LED for over a year from a 48V PSU tweaked down to 43V with this regulator:It gets warm, but is quite manageable, and the LM350 never sees more than a few volts across it.But for a honest 48V that approach is just too hot.

author: georges80
author_rank: Frequent Contributor
timestamp: May 25, 2014, 08:21:04 pm
content: A LED DC : DC boost driver from say around 24V DC input would drive your LED.Linear regulators aren't particularly a good choice unless you know the LED Vf at the desired current and adjust your DC input (to the regulator) to minimise voltage drop requirements (and hence dissipation). Of course that Vf will change as the LED ages and also with temperature.cheers,george.

author: Artlav
author_rank: Frequent Contributor
timestamp: May 27, 2014, 11:06:34 am
content: Quote from: georges80 on May 25, 2014, 08:21:04 pmDo you have any examples?I have troubles finding a parametric search for such things.I also found the hard way that a boost converter can not reliably supply constant current, so how exactly do they work?Quote from: georges80 on May 25, 2014, 08:21:04 pmWhich is why i'm looking for alternatives.Like paralleling LED buck drivers.

author: georges80
author_rank: Frequent Contributor
timestamp: May 27, 2014, 03:14:13 pm
content: I make/sell such a boost drive (my signature). But I'm not pushing my product at you, just stating that CURRENT regulated boost drivers do exist and are designed to drive LEDs from a lower input voltage supply.Not sure what problem you've had in the past, but such drivers exist and work fine. They key with a boost driver is that is will draw more and more current as the input voltage drops. So, you have to ensure that the input voltage range remains within the operational limits for the driver - ESPECIALLY the input current.E.g. if you had say a LED array that required 40V at 2A, then you have 80W load. Ignoring efficiency losses, let's assume you then have 80W at the input. Now, with say 20V input the driver would then draw 80W/20V = 4A from the supply. Say the driver had a limit where if the input current went above 6A the driver would be at the limit due to saturation in the inductor. Now you try to lower you input voltage to 10V, the driver would then need to draw 80W/10V = 8A and it would exceed its safe operating maximum of 6A. The inductor would saturate and efficiency would drop (a lot). Current through the power switch of the driver would sky rocket and you would likely destroy the power switch device (typically a FET).So, a boost is more problematic and requires choosing an appropriate power source or providing some kind of cutoff to prevent the driver operating when the input voltage dropped too far (discharged batteries etc).cheers,george.