Driving LEDs (Samsung LM301B) with Arduino - Page 1
Forum section: electronics / projects

author: T_guttata
author_rank: Regular Contributor
timestamp: July 25, 2021, 06:09:54 pm
content: HiI would like to control LEDs with a constant current IC with an arduino (PWM). Power source shall be 12V (CV).I want to use Samsung LM301B chips with 200 lumen/W:https://www.samsung.com/led/lighting/mid-power-leds/3030-leds/lm301b/#For current regulation I thought to use the BCR 430U from infineon, which has a very low voltage drop pf 0.135V.Could anyone give me a feedback, if the following circuit will work:The BCR421U (Vdrop=0.95V) might work as well (430U seems hard to get).For my understanding: 4x2.7V = 10.8V voltage drop across the LEDs. What happens with the remaining 1.2V? Is it correct to say that the advantage of the BCR430U is that 11V would still be sufficient to drive 4 LEDs while for the BCR421U you actually need 12V?Thanks for your explanations!

author: mariush
author_rank: Super Contributor
timestamp: July 25, 2021, 08:05:26 pm
content: The excess voltage will be dissipated inside the linear driver chip. In case of both chips.ot sure how you use the mosfet is good, it may be a better idea to just use a led driver chip with a built in enable / dim pin so that you can send a pwm signal directly from your arduino..Whatever you spend more on the driver chip, you save by not having to use that mosfet.For example have a look at BCR421UW6-7 :https://www.digikey.com/en/products/detail/diodes-incorporated/BCR421UW6-7/5247740162k in stock at Digikey, defaults to 10mA but can use external resistor to go up to 350 mA, and has enable pin that you can pwm from arduino (25 khz) to dim.There's also BCR401 in same footprint, which is limited to max. 100mA (your leds are ~ 65mA so it would be fine for your needs) :https://www.digikey.com/en/products/detail/diodes-incorporated/BCR401UW6Q-7/7352843Another good option would be DLD101, which uses a mosfet inside the chip instead of transistors, so less worries about how much voltage is dropped inside the chipHere's link to it :https://www.digikey.com/en/products/detail/diodes-incorporated/DLD101-7/2217122

author: T_guttata
author_rank: Regular Contributor
timestamp: July 25, 2021, 10:01:32 pm
content: Thank's for your reply. The BCR421 sounds nice, and yes according to the datasheet you could use that directly with a microcontroller. I would prefer to have the mosfet on another pcb than the LED pcb. This way I could design a control PCB (with space for arduino nano) and I have the LED pcb, which can be seen as a lamp. I could therefore use the control PCB either for custom shape LED pcbs (jlcpcb sells alluminum pcbs which I want to try) but as well for led stripes.There is a BCR421U from infineon and one from Diodes Incorporated. The one from infineon only goes to 200mA, but it's still way more than 65mA.Could I set 2x4 LEDs in parallel to reduce the amount of driver chips?In case I don't use the MOSFET, could I use several driver ICs on the same arduino I/O?Most LED stripes seem to use only resistors, but no current control ICs. I have a 24V stripe with 7 LEDs in series, which is approx. 19V. I measured the voltage drop across the resistor, it's approximately 4V. Maybe using current control ICs is overkill?

author: mariush
author_rank: Super Contributor
timestamp: July 26, 2021, 04:37:29 am
content: Yes, you can parallel leds to use more leds with a driver ... but keep in mind the current doubles, so the led driver must be configured for 130 mA instead of 65mA in your case.A resistor is a basic current limiting method. It drops some voltage and that's it, you can't control it.A LEDs forward voltage is not fixed. It will vary with temperature, it will also be different between leds in the same series.So for example, taking your led :https://cdn.samsung.com/led/file/resource/2020/09/Data_Sheet_LM301B_CRI80_Rev.10.1.pdfYour leds have a forward voltage between 2.6v and 2.9v, depending on binning (there's 3 binnings) and luck.Then you go on page 13 and you can see there forward voltage vs current and you can see that at 65mA, you kinda need around 2.8v forward voltageThen you look at relative forward voltage vs temperature and you can see that at 80c, the leds forward voltage will drop to around 97% of original forward voltage, let's say 2.72vSo you do your initial math for the resistor with 2.8v in mind ... 12v - 4x2.8v = 0.8v / 0.065A = 12.3 ohm so let's go with 12 ohm because it's in E6/E24 etc. and the power dissipated in the resistor p = i squared x r = 0.065 x 0.065 x 12 = 0.0507 watts so you can use a surface mount resistor (0.1w) and be safe.But as the leds go up in temperature their forward voltage drops, so they'll use more current and your resistor is fixed so it can't keep the current fixed. It won't increase by much as the variation in forward voltage is not that high but still, there is some.Also, if one led dies shorted, then the remaining 3 leds get way more current going through them and you could get a chain reaction of leds blowing upA led driver would adjust the current when/if a led dies shorted.