MP24833 based LED light - Page 1
Forum section: electronics / projects

author: jfort1234
author_rank: Newbie
timestamp: June 13, 2024, 04:33:53 am
content: So, to summarize the big project I have started on (I have a lot of big ideas I give up on, hopefully I will finish this one):I am designing an addressable RGBW LED pendant/orb light system, which I intend on making a control unit to convert from some standard (artnet, DMX etc) to a proprietary SPI-based protocol. I plan to use two LTC6820s in each light, which is a transceiver that converts the SPI to a differential pair. I will basically make an SPI loop, and the MCU in each light will basically act as a shift register similar to WS2812 LEDs. I also plan on using PoE ethernet magnetics so that I can send DC over the cable (I plan on using cat5e STP from light to light). I then will have a PIC or some other MCU (On that note, I wanted to use a wide-range LDO that will power the MCU directly from whatever voltage comes in). The MCU will output PWM for each channel R/G/B/W to an MP24833 in buck-boost mode.The MP24833 in buck boost mode is where my confusion lies. I realize there might be no actual reason to use it in buck boost mode, it would be much simpler to just make sure the input voltage is always higher than the output voltage and just do buck mode so there isn't separate AGND and VSS. But my idea was just to have the flexibility of powering them with a wider range of voltages and re-using the board with different amounts of LEDs and different forward voltages etc. I understand the schematic, it's just that the sample layout seems to show either buck or boost mode but not buck-boost. The buck-boost schematic shows LED+ being connected to AGND (I understand that connection is how L1 gets energized/charged, when the internal FET is switched on, current goes through L1 to AGND). But the sample layout does not show the connection between INGND and AGND. Should the two be connected via a trace, or can I make a copper pour/filled zone with AGND/INGND on the whole board?Also, do I need a different VSS for each of the 4 buck-boost converters on the board? I'd imagine yes, it must be separate for each because it's a floating ground. I think I could probably design a board that *works* I'm just not sure I'm knowledgeable enough to design something that works reliably, has no thermal issues, and has no EMI/RFI/crosstalk issues. I think to make this idea more easily come to fruition, I will first just design a single buck/boost board and power some white LEDs with it (and just send PWM from an arduino board) before attempting the bigger project.TLDR How do I connect AGND to LED+ as per this schematic? This is my first post please go easy on me

author: Phil1977
author_rank: Frequent Contributor
timestamp: June 13, 2024, 06:27:29 am
content: There´s nothing as a free lunch...There´s a good reason that buck/boost mode is not used that often. It´s just less efficient than pure buck or boost topologies. So usually there are two use cases:- a low impedant, low voltage power supply is given: Put as many LEDs in series as you need to raise their minimum forward voltage over the supply voltage. Then use boost mode.- long supply lines are needed: Use a power supply that has sufficiently high voltage for buck converters.Always remember: If you don't know what quality of your circuit should be optimized, choose efficiency! Even in large industrial projects there is nothing worse then experiencing in the late design phase that the competitor has better efficiency. You can engineer more or less around all other parameters of the system, but if efficiency is once sacrificed, it´s extremely expensive to get it back.Boost buck mode sounds omnipotent, but if there is no specific need for it it makes things less efficient and more complex.

author: jfort1234
author_rank: Newbie
timestamp: June 13, 2024, 09:31:31 pm
content: Thanks! I think I will just use the buck configuration. I suppose since I plan on using ethernet cable that's 23ga or 24ga it would be best to just do 48v anyway given the small gauge of the wire.

author: mariush
author_rank: Super Contributor
timestamp: June 13, 2024, 11:05:20 pm
content: You're choosing all kinds of expensive chips for this.If you're not gonna use ethernet through the cable, why would you bother with magnetics / transformers in the ethernet jack?For up to 100 mbps ethernet only two pairs are used out of the 4 and it's an established standard to have passive power over ethernet, where the two unused pairs are used for voltage and ground, up to around 56vYou could use RS485 transceivers, Renesas makes some half duplex or full duplex RS422 or RS485 transceivers that can go up to around 50mbps and up to something like 4000ft, and can work on ethernet cableSee for example :https://www.digikey.com/short/52j7hh80LTC6820 is like 6$ a piece, you can get a full duplex 10-20 mbps IC for something like 1.5$ a piece and if you want isolation you could use some optocoupler or digital isolators between your microcontroller and the transceivers.A buck regulator that converts up to 60v to something like 5v-12v is also easy to find...some examplesAP66300/ AP66300Q : up to 60V in, up to 3A out :https://www.digikey.com/en/products/detail/diodes-incorporated/AP66300FVBW-13/17126063orhttps://www.digikey.com/en/products/detail/diodes-incorporated/AP66300QFVBW-13/17736722Richtek RT6362 : up to 60v in, up to 2.5A out, configurable frequency:https://www.digikey.com/en/products/detail/richtek-usa-inc/RT6362GFP/16376760orhttps://www.digikey.com/en/products/detail/richtek-usa-inc/RTQ6362GQW/12091100(qualified for automotive part)You have example circuit of 8v..60v in, 5v at 2.5A out, 500kHz at page 14What leds are you planning to use in your project?Depending on current per color, it may be cheaper or more convenient to use a single buck converter or two buck converters to get the voltage above the led forward voltage by around 2-3v and then use a linear driver or cheaper led drivers with lower maximum input voltage.For example let's take these leds :https://www.tme.eu/gb/details/pblb-3lte/colour-power-leds-emiter/prolight-opto/or warm white versionhttps://www.tme.eu/gb/details/pblb-3lte-rgbv/colour-power-leds-emiter/prolight-opto/They're 300mA max per color, max 2.7v for red, 4v for green, 3.9v for blue and white , in total at 300mA you'd have 1.2A ... so if you configure that buck regulator to output 5v up to 2A or so, you'd have 1.2A for the led, and the rest for microcontroller and transceivers.You could then use cheap BCR420/BCR421 if you don't care about super fine brightness control, or you could use something fancier likeDLD101 (linear, up to 1A) -https://www.digikey.com/en/products/detail/diodes-incorporated/DLD101-7/2217122-https://www.diodes.com/assets/Datasheets/ds32007.pdfor buck driversIS31LT3350 (up to 750mA current, works with 6v to 40v, adjustable with pwm) :https://www.digikey.com/en/products/detail/lumissil-microsystems/IS31LT3350-V1SDLS2-TR/4286476AL8860 (max 40v, max 1A for the TSOT25, 1.5A for MSOP)https://www.digikey.com/en/products/detail/diodes-incorporated/AL8860WT-7/6226978AL8862 (max 60v, max 1A, DFN, SO-8EP )https://www.digikey.com/en/products/detail/diodes-incorporated/AL8862FF-7/14825822https://www.digikey.com/en/products/detail/diodes-incorporated/AL8862SP-13/8120423https://www.digikey.com/en/products/detail/diodes-incorporated/AL8862QSP-13/10670150honorable mentionAL1792AFE and AL1793AFE (2 channel or 3 channel, 0.5A per channel linear led driver, needs minimum 6.5v to work, max 30v)https://www.digikey.com/en/products/detail/diodes-incorporated/al1792afe-13/5358135https://www.digikey.com/en/products/detail/diodes-incorporated/AL1793AFE-13/5358136

author: jfort1234
author_rank: Newbie
timestamp: June 21, 2024, 01:24:06 am
content: The chips seemed cool thoughbut you're right, there is no point using an expensive SPI transceiver when I could just use RS485. Actually, I have changed my mind a little, since these will be pendant type lights, I may as well just have the driver be at the top, and then just run separate power wires and cat5e in conduit or something. Then I could use 18ga or some larger conductor. The driver can just mount directly to a normal (north american) octagon type electrical box. And I can just run that low-cost 5-conductor "LED" cable down to the light which will just be the LEDs with no active electronics. I could also have the drivers use standard DMX which just would still use RS485 transceivers. I still want to use a buck driver for each color channel though, I just like the added efficiency that's all. The AL8862 you mentioned seems like a good idea. Within my anticipated range of 42-57v it would remain over 93% efficient at an output voltage of 36V.This is really just a personal project, but I still would definitely market and sell it if I made a viable product. Since I want it to be more of a thing for commercial installations anyhow, and they have to be mounted to the ceiling in one way or another, it makes sense to just have the driver at the ceiling and then a "dumb" light down below. It seems like a trivial step to require the installer to run a conduit with wire and cat5e inside.