How do I drive LEDs without flicker ? - Page 1
Forum section: electronics / beginners

author: DeadlyChemist
author_rank: Regular Contributor
timestamp: March 15, 2022, 10:28:39 pm
content: Hey,First some background:I have been struggling with LED lights for 4 or 5 years (or maybe more...)They usually fall in multiple of these categories:unpractical / big / super expensive | (never bought)awful color quality | (skin looks green/magenta, super hard to remove in post even with correct tint/WB)too dim (the placement in my room is pretty bad so need multiple ones anyways but that’s fine)flicker, flicker, flicker, I like to make nice videos and I like to be creative with my framerate and shutter angleThey just die very fast due to probably overheating?What I plan to make:Custom celling lights!Decent quality (~95 Ra ~90 Re) lightHigh BrightnessUnderdriven LEDs on a big heatsink (should increase the life massively)RGB-whatever for casual party (and red to keep nightvision)basically a overkill light I can enjoy and fix for many years to use both as a room light, recording light (well, from above at least) and other purposeseverything should be dimmable (more below).What I have:bunch of designs, testsBasically got the heatsinks/frame figure out, as well as Decent Quality LEDs, basic idea of the software, what features I want, over-whatever protection, both software and automatic (like fuses, other things)What I don’t have:didn’t order many parts (more below)a working LED driver ☹ (more below)fan-less power-supply (I’ll deal with it last myself, don’t worry about it)So basicallyFirst thing I went for is well, googling, after hours of looking at sold out super expensive chips , I resorted to ask on random discords, everyone suggested PWM, but I feel like that would flicker pretty badly? (please tell me)later someone suggested using lm2596 CC CV module likeTHISlooking at this diagram from some weird websiteLINKit shouldn’t flicker? It’s only 300mV at 48kHz (also I would use max 1A per module)I already had one and bunch of 5W leds, so powered them up on nearly max (mistake), pointed my camera (120fps 8.6°) and didn’t find any flicker also made sure they can deliver 1A over long time while being pretty insulated (they got warm but not really hot)So instead of using a trimmer to set the voltage and current, I set the voltage using trimmer and used a MCP 4461-103E/STMCP 4461-103E/STdigital potentiometer for current (ordered 8, needed 6 to power 1 light)took me about 6.5h to write a working I2C code… oh wellso I pointed my camera at 5W LED and used I2C to change the potentiometer wiper position (because the potentiometer controls the current to the LED) and well, it flickers, badlyI repeated the experiment with unmodified lm2596 module, used pots to set the current lower and lower… the flicker appears, gets worse and worse. So I feel like lm2596 is dead path? Please let me know!I’m pretty sure I can throw these chips away (put into “forever” parts bin) which well, my fault, didn’t test enough but kind of unfortunate ☹But anyways, what options do I have? How do I dim a light without flicker, I feel like even at 1MHz there will be flicker (let’s say I rented phantom v2512 and shot video at 500k fps and 10° shutter speed, for whatever reason) isn’t there another way than PWM? Or am I just wrong?For white leds (majority) I don’t really need “infinite” brightness levels, I’d say 10 is ok, but seamless would be even better. For RGB it’s a must because of mixing.Also I would prefer something “easy”, I do not have 100’s of euros to just prototype and find out 99% does not work. My budget for the project was 200€ per light, but would end up at around 300€ (the drivers were 30-40ish euro I think)The leds I wanna use are 23V 300mA (would limit to 225mA) cool white + warm white in 4x4 matrix so 32 LED dies but was thinking to put them in 2x pairs (I know one should not do this) (plus like 5 rgb ones in the middle…)What options do I have?, Please help !note: by flicker i mean anything from visible turning on-off to weird bands on the walls or similar. when i test with sunlight or battery and resistor, i do not get that

author: free_electron
author_rank: Super Contributor
timestamp: March 15, 2022, 10:38:38 pm
content: you need a current mode driver. a LINEAR one, not switching.

author: DeadlyChemist
author_rank: Regular Contributor
timestamp: March 15, 2022, 10:44:25 pm
content: Can i have an example please? also how would i change the current with a microcontroller? (i.e. get dimming working)

author: DeadlyChemist
author_rank: Regular Contributor
timestamp: March 15, 2022, 11:22:15 pm
content: Quote from: pigrew on March 15, 2022, 11:07:11 pmHi, here is the linkhttps://www.aliexpress.com/item/1005003210480731.htmlthey aren't amazing, but decent, the quality is decentI sadly do not have a scope, storage is premium and pc/handheld ones arent worth it in my opinionwell, also i need to controll it with micro so i can get my brightness adjustment. and i have no idea how to achieve that... 4x4 leds each with 2 channels... so that's 32 leds, 16 if i group thenI dont really care about efficiency... the amount of leds i would use is MAX 170W, so burning like 30W or 50W or whatever in inefficiencies is fineis there some easy proof of concept i can make/buy and test? 23V 225mA or 23V and 450mA (or maybe someone can do me a favour...)I really dont know what's best / works, so i'm happy to use whatever you guys offer...

author: OM222O
author_rank: Frequent Contributor
timestamp: March 16, 2022, 12:06:56 am
content: You can build a constant current source pretty easily, if you have the digital potentiometers, you don't even need to order many more parts.look at this basic schematic:https://tinyurl.com/yc9kgv2sThe potentiometer acts as a voltage divider to provide a voltage reference between 0 and 5 volts. The op-amp uses that voltage and a reference resistor (100 ohm here) drives the MOSFET so that the output current equals reference voltage/reference resistor (here it would be from 0 to 50 milliamps (5v / 100ohm) ). All of the unused voltage will be applied across the MOSFET, which will heat it up, so make sure to use a heatsink and add as many LEDs in series as possible (to calculate that subtract the max reference voltage (5v) from the supply voltage (12v) and divide by the maximum voltage of the LEDs at their peak current).If you have time, it'd be worth replacing the voltage source with a boost converter which allows for fine adjusting the voltage, so that the heat dissipated in the MOSFET is always minimum. To do this, just measure the voltage drop across the MOSFET with a differential op-amp that connects to your micro controller's ADC. then use another digital potentiometer to adjust the feedback resistor of the boost convertor so that the voltage across the MOSFET is a low value (for example 500mV). Here is an example of how to do this: Adjust your brightness and set the voltage source to its maximum output value (let's assume 12v). Then measure the voltage between the drain and source of your MOSFET (using differential amplifier connected to ADC). Assume it reads 2 volts, but you want it to be 500mV, so you need to lower the voltage source by 1.5V (12 - 1.5 = 10.5).

author: DeadlyChemist
author_rank: Regular Contributor
timestamp: March 16, 2022, 12:26:03 am
content: Quote from: OM222O on March 16, 2022, 12:06:56 amwhat mosfet would you recommend? what specs am i looking at even?also, the specs of op-amp shouldn't matter?i played with the simulation a little... looks like in this case i need 20R or sohow would i calculate the power needed for both resistor and mosfet? like this:the leds I plan to use are 22.4V maximum24V power supplies are easy to come byso let's say i need 8 amps for all of themso basically (24-22.4)*8 =~16W? how is that split between resistor and mosfet...? 16W does not look like a big deal when you split it up between many modules...The only thing i don't like is that the 0-5V need to be precise-ish, else the current goes way up, but because op-amp is in follower mode + it's a gate of a mosfet I assume we are talking miliamps for 10's of modules?what should i be cautious of? anything that can be upgraded here? any component I need to take extra care of?if i wanna control 2 leds, i could just feed 1 pot into 2 opamps and get 2 nearly exactly same current sources?are there better approaches? (this looks very cheap tho, I like it)

author: OM222O
author_rank: Frequent Contributor
timestamp: March 16, 2022, 01:16:23 am
content: Power is simply voltage X current. The voltage across the resistor is always going to be exactly the same as the reference voltage (0 to 5v in simulation) and the current is Vref / Rref. The voltage across LEDs depends on their voltage-current curve. Whatever remains (Vsupply - (Vref + Vled)) is applied to the MOSFET. Current will be the same for all of them, so it's a basic multiplication step to find the power (or you can hover your mouse over the component in the simulator to find these values).The only things to look for: Op-amp MUST be rail to rail input/output for these low voltages, other characteristics don't really matter, but a low input offset (less than 10mV) would be nice. If you want to connect the reference voltage to multiple op-amps, using a voltage follower on the output of the voltage divider would be a good idea.If you plan on using a 24V supply and 23V LEDs, that leaves 1V for the reference voltage, which means a resistor value of 4 ohms. 1.024v reference ICs should be easy to find and they'll be a perfect fit here.The only thing to look out for the MOSFET is the safe DC operating area (middle left chart on page 6 of this datasheet:https://www.mouser.co.uk/datasheet/2/308/1/NTP125N65S3H_D-2318962.pdf(there is one table of contents page so it's labeled as page 5 on datasheet itself). For 1 amp, it should be safe to around 100 volts, but this is specified for a temperature of 125c. I think you'll be fine using this for 250mA and a max voltage of less than 10V. It's not a super cheap fet, so feel free to look at other datasheets. If you use a normal fet, you should also drive the Op-amp with a suitable voltage range (12 or 16v). I've never used this IC before but it seems to be a good fit: TLC2252https://www.ti.com/lit/ds/symlink/tlc2252.pdf?HQS=dis-mous-null-mousermode-dsf-pf-null-wwe&ts=1647392636961.If you can find a logic level fet with a suitable DC operating area, then you can use 5v for the op-amp so something like the MCP6002 would be nice. The only problem is that most logic level fets can't handle 24V drain-source voltage. This is the most annoying part of any project because you have to browse datasheets and use filters to find suitable parts that can work together.I'm not really sure what you meant by: "The only thing I don't like is that the 0-5V need to be precise-ish, else the current goes way up, but because op-amp is in follower mode + it's a gate of a MOSFET I assume we are talking milliamps for 10's of modules?" can you explain again?The only thing you need to be careful of would be the op-amp oscillating. You can't really measure this without a scope but you can add resistors and capacitors to the feedback of the op-amp to stabilize it. If you build a prototype and it works, don't worry about it.I also suggest you control each LED channel separately using copies of this circuit. Have a look at this simulation:https://tinyurl.com/yccd49w4The only other approach would be PWM which will cause flickering, if you want a constant current solution, this would be ideal and cheap.Edit: ignore anything I said about using a boost converter and adjusting the supply voltage. When you drop the current, the voltage does increase across the mosfet, but the decrease in current results in a net reduction in waste power. maximum heat would be at maximum LED brightness, so choose your values based on that.

author: tooki
author_rank: Super Contributor
timestamp: March 16, 2022, 12:23:17 pm
content: PWM is fine (and in fact a great choice) if done at a high enough frequency. I made a dimmer (in daily use at home) with a PWM frequency of something like 25KHz, and it’s absolutely flicker free.

author: OM222O
author_rank: Frequent Contributor
timestamp: March 16, 2022, 12:27:11 pm
content: depending on the framerate of a camera and the drive frequency of the LEDs, there will always be flickering, unless they perfectly sync up (drive frequency being an exact multiple of the framerate). That's exactly why they always use a linear driver for the light sources when filming with a high-speed camera.

author: wraper
author_rank: Unknown
timestamp: March 16, 2022, 12:35:42 pm
content: Quote from: free_electron on March 15, 2022, 10:38:38 pmWhy would you need linear? You just need to avoid PWMing the LEDs directly.

author: cdev
author_rank: Super Contributor
timestamp: March 16, 2022, 12:53:14 pm
content: Is there a way you can use regulated DC?You just have to avoid an overcurrent situation.

author: Siwastaja
author_rank: Super Contributor
timestamp: March 16, 2022, 02:27:13 pm
content: Of course a switching converter.Current controlled, totally.You can add output capacitance but it isn't really needed; if the converter runs in CCM at some hundred kHz, the "flicker" (really just the inductor current ripple, maybe 30-40% of the intensity, not fully on/off) is at such high frequency it isn't visible to any living object or even high-speed photography!Of course, high enough frequency PWM is fine too, but there really is no need in general purpose illumination, IMHO. Better use adjustable current in the supply. For very low output level, further PWMing may be necessary, though.Start by looking at LED driver ICs; typical topologies are buck or boost. Current poor availability of everything makes selection process easier, look what you can buy, and look for current feedback / constant current operation.

author: tooki
author_rank: Super Contributor
timestamp: March 16, 2022, 04:03:37 pm
content: Quote from: OM222O on March 16, 2022, 12:27:11 pmThe faster the PWM, the less it matters that it sync up exactly. I have actually tested mine with various cameras. Up to the 1/500s of my DSLR, and even the 240fps slow-mo of my phone. Absolutely no flicker or banding. The frequency is so much higher than the shutter speed that it doesn’t matter.

author: DeadlyChemist
author_rank: Regular Contributor
timestamp: March 16, 2022, 07:36:54 pm
content: EDIT:I might try with 5R resistor and 1-whatever volt referencethe simulation gives me range between 1mA and 203.8mAthe leds are 300mA leds, but i wanted to drive them at 225mA (75% power)66% power isn't that bad... not ideal but not bador 4.5R, not sure what i can get easily and cheaply (again i have 4x4x2 leds to drive)Quote from: tooki on March 16, 2022, 12:23:17 pmI'm pretty sure it will flicker at at 25k fps and 90° shutter...Quote from: tooki on March 16, 2022, 04:03:37 pmwhat shutter speed/angle? 1/500's is only 2ms (if my math is correct)with my 120fps and 8.6° i'm getting 0.19ms per frame (if my math is correct)for my tests i just go to 120fps 360° and slowly decrease to 8.6° (can't go lower sadly)later I import the footage and slow down 2x to 60fps and just watch it and look for weird shit like banding or litteral darker and brighter framestried with sunlight and there is none of that weird stufftried with the dc-dc converter that apperanty runs at 48khz and you can see terrible results above at lower powermy shutter is rolling so that "helps" with finding such weird things...Quote from: cdev on March 16, 2022, 12:53:14 pmI'm asking you ? I tried my stuff and it failed so i'd appreciate if you guys can throw another idea (wil the the mosfet one)Quote from: OM222O on March 16, 2022, 01:16:23 amI can just use another power source or use the 24V for the opamp...most likely i'll use 3.3V micro but not sure...yeah iirc op-amps cost pennies so i don't mind...Quote from: OM222O on March 16, 2022, 01:16:23 amnot sure how that works or what that means but yeah, i'll try these values...if i want 250mA max then 1W 4R and basically any mosfet with enough voltage? please confirm/denyQuote from: OM222O on March 16, 2022, 01:16:23 amso what you basically say is, use the 24V power supply or something high for the op-amp and get the cheapest fet with decent characteristics...?Quote from: OM222O on March 16, 2022, 01:16:23 amdoesn't matter anymoreQuote from: OM222O on March 16, 2022, 01:16:23 amwell i'll first try a prototope on breadboard (and post results here...), then probably move to pcb...also planning inbetween...Quote from: OM222O on March 16, 2022, 01:16:23 amI could have done this years ago with a cheap 100W led with a scrap heatsink and a cheap 100W led driver and a horrible dimmer"great" for general lighting or soldering or whatever but useless for photo/video (flicker and color quality)Again, i'm not shooting everyday at 100's of thousands of fps with single digit shutter angle, but i wanna make something that can handle any camera, I do not want to be limited in my creativity just because my lighting sucks (current plan is to make 3 of them...that would be 9000 lumen cool 9000 lumen warm times 3it is overkill and unnesecary 99% of the time, but for me it's like buying a ifixit tool tech kit just to take apart a broken nokia 3310, it's investment for later)are there other good appreaches except mosfet? I'll take a look in few days for partsnext few weeks i would order:I guess any mosfet that can handle few watts with max 30V or more...then any op-amp, 1V reference and 4R 1Wpowersupplies i have a bunch of things, this is just a test anyways to see if it works@OM222O please verify

author: strawberry
author_rank: Super Contributor
timestamp: March 16, 2022, 08:14:06 pm
content: LM2596 feedback loop oscillate (maybe ~100Hz)due to bad circuit design(or fake IC) . need some oscilloscope waveform and circuits to confirm.

author: DeadlyChemist
author_rank: Regular Contributor
timestamp: March 16, 2022, 08:34:50 pm
content: Quote from: strawberry on March 16, 2022, 08:14:06 pmdon't have a scope...also it oscilated pretty bad at lower power only... again, not sure... cheap module, but had higher hopeswhat other options do i have except mosfet?

author: OM222O
author_rank: Frequent Contributor
timestamp: March 16, 2022, 09:05:49 pm
content: If you have 4x4 LEDs (16 panels), each with a warm and cool channel, you will need 32 copies of the current sink, which is not ideal, but if you choose lower spec parts, it shouldn't be too expensive.I had another look and this cheaper MOSFET should also be fine:https://www.diodes.com/assets/Datasheets/DMT6009LCT.pdfyou don't need to drive the op-amp with 24v, 12 to 16V should be enough. It just needs to be able to drive the gate of the MOSFET with a high enough voltage to turn it on, which is around 12v for most MOSFETs. higher voltage op-amps tend to not be rail to rail, but I found this quad-channel one to be reasonably priced:https://www.mouser.co.uk/datasheet/2/308/1/MC33201_D-2315666.pdfThe op-amps don't draw much current, so you can even use an LDO to generate the 12V or 16V from the 24V supply.I updated the simulation to show you the math of how to budget the voltage for the LEDs, voltage reference, and MOSFET. Instead of connecting a bunch of LEDs, I just used a 22.4 voltage reference.https://tinyurl.com/y8g4dllrThe power dissipated in the resistor will be around 1 watt at 250 mA, so ideally choose a higher rated resistor. A better choice would be buying a pack of 1 ohm, 1-watt resistors, and connecting 4 in series to get a 4 ohm, 4-watt resistor (dissipating the heat over multiple components). This should end up being cheaper and give you more flexibility in the range of values you can create. For example, to get 4.5R, you can put 2 1R in parallel to get 0.5R, then put that in series with 4 1R to get 4.5R.You don't need to buy the exact parts I posted, anything similar should be fine. buy a few for prototyping and if it worked as you expected, then order the parts for all 32 channels and design a PCB for it.

author: DeadlyChemist
author_rank: Regular Contributor
timestamp: March 17, 2022, 01:08:55 am
content: Quote from: OM222O on March 16, 2022, 09:05:49 pmfoundthisandthisi assume both will work?i'd rather use 2ohm ones but yeah, this is cheap and small enough so might go with it unless i find 2ohm or so ones, for tests i'll use whatever i find.. maybe even bunch of quarter watt onesQuote from: OM222O on March 16, 2022, 09:05:49 pmfound the MC33204 for 1.14€ or so, 30 cents per op-amp not bad but will look for cheaper tbh, or is there a reason i might want something higher quality?i'd say i need 4*4*2 opamps and 1*4*2 followers (will make the micro adjust them in pairs of 4) so 40 op amps give or take, might pick some cheapies for followers... not sure yet... it's just following 0-1v (are there reasons why i shouldn't cheap out on followers?)Quote from: OM222O on March 16, 2022, 09:05:49 pmThank You !Quote from: OM222O on March 16, 2022, 09:05:49 pmwebsite does not loadfound same part tho, 80 cents per piece isn't good but seen worse... maybe 50-70 or less cent range is possible? unless it's not worth the troublenot sure about thermals either? how many watts can the package get rid off on its own? maybe i can bend it over and mount it to pcb somehow (use the copper/traces as heatsink) (just mount it like smd part...) i dont wanna buy/make 32 heatsinks unless i really have to (please let me know)1W does not sound like a lot to get rid of (well times 32...)(the leds will be on a 300x300 heatsink, maybe 400x400 if i feel so (did all the math with overhead already (dont intend to drive both channels at max))math says with 75% maximum (225mA) at full blast (both channels) i'll reach 51C and 85% maximun (250mA) i'll reach 55C (both channels) (both assuming leds are 30% efficient with room temp 25C)so might go for bigger heatsinks for the leds... also not sure what the metal part of the mosfet is connected to? source/ground? then i can hook them all up together with 1 heatsink... then use wires to connect to pcb...also already got a bunch of ideas, might even buy few cheap i2C ADC's and bam, got basically free current measurment for every led (just because I can)did some math on 1% of 4 ohms... worst case i'm getting +- 0.04ohms which is 3 miliamps difference so that's greatthanks for the help @OM222O!sorry for overexplaining, i'm pretty bad at electronics, i'd rather avoid stupid mistakes

author: Circlotron
author_rank: Super Contributor
timestamp: March 17, 2022, 01:39:38 am
content: I'd put an inductor in series with the LED on the PWM setup you already have. An inductor always tries to make the current through itself constant, and consequently the LED brightness will be constant. The actual inductance value will depend on the PWM frequency.

author: DeadlyChemist
author_rank: Regular Contributor
timestamp: March 17, 2022, 01:59:56 am
content: Quote from: Circlotron on March 17, 2022, 01:39:38 amtempted to try...bit feel lile that would be a temporary fix...?can chuck 22uH and try but the option above with mosfet does not sound bad...

author: OM222O
author_rank: Frequent Contributor
timestamp: March 17, 2022, 04:21:35 am
content: I made a really stupid mistake and instead of using (I^2) * R, I just calculated I*Rthe power dissipated in the resistor is actually 250mW, not 1 watt.both resistors should be fine, although 2512 is a huge package. I think if you use 4 1206 ones you should be fine. Or maybe find a 1 watt 4R 2512. Depends on how much time you want to spend on soldering.MC33204 seems like a really nice part. You can try to find cheaper (if you search for 1 channel op-amps with similar specs, you can find many that are cheaper, but it makes soldering them a nightmare if you have about 40 to solder. Feel free to have a look for them though. It'll usually be cheaper if you buy in quantity (buying 10 is actually cheaper than buying 8 ) and 10x4 = 40 op-amps, which should be enough for everything. You can try to cheap out on the voltage follower but it would be buying a separate part for no reason.To see how hot the package gets, multi[ly the thermal resistance by the power dissipated in the MOSFET. The best packages are TO-220 and DPAK. If you want to solder it to a large copper area, DPAK would be easier to use. This one is about 0.5€ if you buy 30 of them.https://www.mouser.co.uk/datasheet/2/308/1/FQD7N10L_D-2313768.pdfIt actually won't be dissipating more than half a watt (simulation says 150mW) so I wouldn't worry too much about heat sinking them, but the most important thing is the safe DC operating area. You can try cheaper MOSFETs that don't have a DC operating curve, but they may die after a while. I personally wouldn't take my chances with that.If you want to use an ADC, a much better option would be buying some thermistors and using the ADC to measure temperature instead of current, because you're setting the current using the digital potentiometer and it'll be fairly accurate with 1% resistors.using inductors/capacitors to smooth out the PWM doesn't sound like a bad idea either, you can try both methods.If you decide to go with my method, it would be a good idea to design a PCB that can only drive 4 MOSFETs (one quad-channel op-amp) and have connectors for daisy-chaining them together (VCC, Vref, GND, etc.) then you can build 8 of them to drive all of your LEDs. This would be easier than designing a massive PCB with all components on 1 board. If you want, I can help you with the PCB design as well.

author: DeadlyChemist
author_rank: Regular Contributor
timestamp: March 18, 2022, 01:20:25 am
content: Quote from: OM222O on March 17, 2022, 04:21:35 amMy time is free, i'll just buy whatever i can get reallyQuote from: OM222O on March 17, 2022, 04:21:35 amwill go with the MC33204 can't be bothered to look elsewhere...cheap enoughas for followers, might pick something else, not sure as of nowgives me a solid base i guessQuote from: OM222O on March 17, 2022, 04:21:35 amfound it onlyherebut i really dislike mouser (stupid fees)will look for something else (unless you can recommend something? (more below))Quote from: OM222O on March 17, 2022, 04:21:35 amyeah, the mosfet looks good, good enough, again, i'd rather overspec...might even buy this and slap it on aswellQuote from: OM222O on March 17, 2022, 04:21:35 amIm actually planning to use 3 (in different spots) ds18b20 one-wire thermometers (as they are cheap and easy to use + can be chained)might even use more as they are dirt cheap, get a heatmap of the heatsink, just because i can lol (more reasons why i'm making my own stuff, i can make it how i want it to be)Quote from: OM222O on March 17, 2022, 04:21:35 amyeah, this would be split obviously + would make a spare pcb when in few years something finally gives upas for daisy chaining, i don't mind running lots of wires... (excuse when i don't know how todo something lol)Quote from: OM222O on March 17, 2022, 04:21:35 amthanks !I willl need that in few months, for now first need todo few tests (few questions below)i prefer to use EasyEDA because it's easy + i order from JLCPCB anyways, I don't wanna exploit you into making a full PCB design, so not sure, maybe i'll just send you file from there or something to just look overthis will be in months from now anywaysAnother question:I'll be using 6 of them(18W variant) (will look kinda stupid, 5 would be better) unless you know an easy way to get 8 or 9 working? voltage between 2.2-3.6V *6 pieces that's 13.2V-21,6V at 500mAif i go into simulation and make a 13.2V led @500mA with 24V psu (worst case scenario)I get 5.2W on mosfetand 0.5W on resistorI assume i can use same op-amp as they are overkill anywaysas for mosfet i think DMT6009LCT with heatsink sounds good but 5W is still a lot to sinkadding more leds won't work because 2.2-3.6V*7 >24Vdo you know of a way to approach/solve this? also how bad is my assumption of "worst case scenario"? i can deal with the 5W of heat but rather notAgain, thanks for the helpdidn't even know this easy path existswill start drawing schematics/writing final features-list as well as build of materialsmight take few weeks...

author: OM222O
author_rank: Frequent Contributor
timestamp: March 18, 2022, 04:05:21 am
content: Edit:DMT6009LCT has a thermal resistance of 55c/w which means it can't get rid of more than 1 watt without a heatsink, if you want to dissipate 5 watts, you will definitely need some sort of heatsink. The ones you posted don't seem to be designed for MOSFETs, I would try searching for TO-220 heatsink. If you want to use the ones you listed, you need to create a large copper area that you can place those heatsinks on, or you may want to try the suggestion below.There sadly isn't an easy way to add more LEDs because the voltage will be too high and you don't have an adjustable output boost converter, but yes, you can use the same circuit to drive those as well. If you want to dissipate the 5 watts over multiple components, you can put a small resistor in series with the LEDs (voltage drop across it will be I*V and power dissipated will be (I^2)*R) this will reduce the load on the MOSFET and distribute the heat over multiple components. You should only need to do that for the lower voltage LEDs (red and yellow). At 500mA you can dissipate 250mW for each ohm of resistance. Here is a quick simulation and you can see without the resistor, the MOSFET is dissipating 5 watts, but with the series resistor, it's about 1.5 watts and the rest is dumped into the resistor. Again you can spread the load across many resistors to avoid the need for a high power 5-watt resistor (for example 7 2R resistors or 14 1R resistors).https://tinyurl.com/yblq3z6pI don't mind designing the PCBs either and I have used easyEDA before so that should be fine. I think you'll like a few of the tricks that I use when designing boards. Just make sure to build a breadboard prototype first to make sure the op-amp will be stable and won't oscillate. If it did, it'll be an easy fix (2 resistors and a capacitor) but you need to know that before designing the final version of the circuit.

author: DavidAlfa
author_rank: Super Contributor
timestamp: March 18, 2022, 06:13:41 am
content: I've used these (380mA version), it's a step-down, non-isollated DC/DC constant current driver.It's high frequency so you shouldn't get any flickering.If so, then it's input ac ripple, increase the input capacitor to 22-100uF.By default it limits the voltage to ~90V (has 100V output capacitor).I modified It for 250Vout, just by changing the resistor ratio and output capacitor, so it could drive a 50W led board (Needs at least ~215V).The current can be modified easily by changing the another resistors.I've tested it from 10 to 50W, didn't overheat.Can't remember the details of the driver IC, but it was pretty capable.https://a.aliexpress.com/_vlrQJB

author: DeadlyChemist
author_rank: Regular Contributor
timestamp: March 22, 2022, 10:02:59 am
content: Quote from: OM222O on March 18, 2022, 04:05:21 amQuote from: OM222O on March 18, 2022, 04:05:21 amyeah, i'll worry about it laterQuote from: OM222O on March 18, 2022, 04:05:21 amI'll let you know, will use the offerfew days ago i ordered one of the leds, should be here in 1-2 monthswill try to get the current-voltage relationship/characterize it to get a better modelalso size, brightness and other factorswill also try to get few parts to test the op-amp and mosfet setupQuote from: DavidAlfa on March 18, 2022, 06:13:41 amyeah i will pass, because with dc-dc or anything switching the current i feel like there will be some framerate/shutter speed which makes flicker... i am so done with flicker

author: DeadlyChemist
author_rank: Regular Contributor
timestamp: April 07, 2022, 07:54:41 pm
content: Small Update:someone on discord told me the 21.0v-22.4v characteristic is incorrect and the range is WAY wider (starting at like 15v)ordered one last monthtested Warm White today:Voltage Current18,90 17,2019,50 43,9020,00 66,0021,00 130,0022,00 230,00the voltage might be inaccurate but the range seems close enoughassuming worst 19V and 50mAthat's about max 250mW to burn on the low endwill also try to see how the defusing/color mixing worksonly had it powered for few minutes but already like it, the warm isn't super red, just slightly warm, cold didn't try yetwill work on the driver/buying parts i think next month

author: DavidAlfa
author_rank: Super Contributor
timestamp: April 07, 2022, 09:12:25 pm
content: What I posted is a constant current regulator (not direct pwm drive), thus no flickering.Add a decent mains capacitor to avoid any 50/60Hz ripple and should be fine.

author: OM222O
author_rank: Frequent Contributor
timestamp: April 21, 2022, 02:01:46 pm
content: Did you manage to test the circuit? did any of the parts arrive?

author: DeadlyChemist
author_rank: Regular Contributor
timestamp: April 21, 2022, 07:43:03 pm
content: Quote from: OM222O on April 21, 2022, 02:01:46 pmI haven't ordered any yet (money problems + monitor needs replacing, beeing jobless sucks lol)I ordered 1 Led to test the color (great!) and tested voltage-current curve (more above)also ordered CHEAPEST 50 mini heatsinks for like 5€ will slap them on the final product (i dont mind weight)Will order some parts prob next month or month after... depends how cheap i can get a 32 inch 144hz or higher used monitor on ebay... *sigh*Will post more updates by thenQuote from: DavidAlfa on April 07, 2022, 09:12:25 pmWill stick to the current method... these regulators would be more expensive as i have 4*4 matrix + 2 channels each... so would need 32 of these boards...

author: cdev
author_rank: Super Contributor
timestamp: April 29, 2022, 01:10:19 pm
content: LEDs simply require a DC voltage and current, a given LED will require a steady current amount.. say 20 ma might be typical for a given LED.So they will provide a constant current driver. They sometimes use PWM above the frequency most eyes can detect flicker. So its not DC buy it looks like DC.You could use DC but how do you vary it? PWM uses duty cycle.. on and off.Computers do this for their fans.They vary the time on and off.

author: Doctorandus_P
author_rank: Super Contributor
timestamp: April 29, 2022, 02:18:04 pm
content: TLDnR.There are two different conceptual problems here.First, When LED's are PWM'ed they blink at the PWM frequency, unless the PWM circuit has some way to keep the LED current steady, for example with an inductor in series with the LED's.Even high PWM frequencies can interact with the shutter time of camera's.Second:When changing the dimmer setting, the light outputs may change in "steps".I think you need at least 14 bits of resolution before the individual steps become small enough to be unnoticeable.And even then, you will probably always see a big difference between 0 and 1, and also between 1 and 2.Human eyes are very sensitive to changes in brightness.

author: DavidAlfa
author_rank: Super Contributor
timestamp: April 29, 2022, 05:20:02 pm
content: Quote from: DeadlyChemist on April 21, 2022, 07:43:03 pmWhat? It's using rectified mains. Put them in 8series*4parallel array with 0.1R balancing resistors, you'll get 160-180Vf.I've driven a 100W ~200Vf led array with it, just had to replace the output capacitor and the voltage limiter feedback resistor which is 100V by default in that design. The controller can handle up to 400V or something like that.It's a high frequency buck converter, you don't get any flickering at xxxKHz, the only possible issue could be being a non-isolated converter, not a problem if you properly ground the lamp.

author: DeadlyChemist
author_rank: Regular Contributor
timestamp: June 08, 2022, 12:52:30 am
content: Update:bought 16x MC 33204 (the op amp)only need like 10 but yeah, i prefer spares than paying shipping againmost likely next month will get the transistors as the fees on mouser are bit expensive :/with resistors I will deal some other time (at pcb desigh state), and voltage reference i have no clue what to pick.

author: OM222O
author_rank: Frequent Contributor
timestamp: June 09, 2022, 02:29:52 pm
content: The voltate refrence isn't critical here, buy whatever is cheapest / easiest to find. It can even be as simple as a 1v zener but to be honest since you only need 1, I'd go with a 1.024 IC because they're more stable.For PCB, you need to design 2 boards: a control board that produces the different voltage levels for each LED (control board) which houses the voltage refrence, digital pot, micro controller etc. Then you have to design a second board that has the mosfet, op amp and sense resistors (power board) which takes VCC (24v) and the control voltages from the control board. If you're using the quad op amp, each power board can handle 4 LEDs

author: DeadlyChemist
author_rank: Regular Contributor
timestamp: June 10, 2022, 01:19:44 pm
content: Quote from: OM222O on June 09, 2022, 02:29:52 pmyeah, i'll just get something from digikey/lcsc when im ordering the transistors/resistors there, temperature sensors, thermal/current fuses and other stuff i'll most likely get from aliexpress, good enough for meQuote from: OM222O on June 09, 2022, 02:29:52 pmthats a worry for later, also found another small issue, but that can be dealt with lateronce i get the transistors and run few tests i'll make schematics...thanks for your help !

author: wraper
author_rank: Unknown
timestamp: June 10, 2022, 03:05:42 pm
content: Quote from: DeadlyChemist on June 10, 2022, 01:19:44 pmMost if that is usually counterfeit on Aliexpress and in most cases dirt cheap on LCSC, unless you want western branded stuff. And using counterfeit fuses is not smart as minimum and potentially very dangerous.

author: DeadlyChemist
author_rank: Regular Contributor
timestamp: June 18, 2022, 02:35:37 am
content: Quote from: wraper on June 10, 2022, 03:05:42 pmtrue, but i trust them enough actually, they arent that bad + fuses are only ment for huge overcurrents anyways, the only thing i won't order from questionable sources is the power supplyas for counterfeit stuff, i usually don't care, they perform the same way as original ones as the margin of error is huge (never had issues when fixing stuff with ebay/alli junk)and stuff like "normal" caps or resistors, i can't care enough, never had issues (because never needed precision parts?)guys, might need help with the transistor, i dont think i wanna pay 50€ or more for 40 transistors because both digikey and mouser have like 20€ fee..., (technically need only 32 but 40 would be good)i need something available in more places :/also i'm moving across country next month (600 km) so this project will get delayed by about few months untill i can pack and unpack all my gear and start working on this again... *sigh* + money ofc

author: tooki
author_rank: Super Contributor
timestamp: June 18, 2022, 11:33:14 am
content: Well yeah, it’s stupid to pay the 20€ shipping for small orders. If you need 30€ of product, just spend 25€ more on other stuff you need so that you hit the minimum for free shipping (€50). I always maintain a list of low-priority things I want, but don’t need urgently, to use as “padding” for small orders, be it soldering supplies, standard components I’m getting low on, wire, tools, microcontroller boards and eval boards I wanna play with, etc.

author: tepalia02
author_rank: Regular Contributor
timestamp: June 18, 2022, 12:54:31 pm
content: Constant current LED driver circuits may help.

author: DeadlyChemist
author_rank: Regular Contributor
timestamp: June 18, 2022, 02:12:57 pm
content: Quote from: tooki on June 18, 2022, 11:33:14 amEDIT: the fuses seem like a crappy idea tbh, the leds can do max of 300mA but willing to drive them with 250mA, looking at blow characteristicshttps://belfuse.com/resources/datasheets/circuitprotection/ds-cp-c2q-series.pdfit just looks like crappy idea tbh.true, but then not sure what could i want from digikey, ~35€ is the max i can think of, unsure what i can fit for 15€, i rarely need electronics parts and when i do i just buy a bunch of random kits for aliexpress to havefor 35€ i can get 50 transistors (need 32) 200 1ohm resistors (need 32*4) and 2 voltage references (need 1)this gives me spares when i do break something, which is good !maybe i can get some overpriced fusesmaybe thishttps://www.digikey.de/de/products/detail/bel-fuse-inc/C2Q-300/615176300mA fuse, 40 of them = 10€, kinda useless but yeah... could get itideas?Quote from: tepalia02 on June 18, 2022, 12:54:31 pmthis is what i'm trying to build

author: OM222O
author_rank: Frequent Contributor
timestamp: June 22, 2022, 10:21:48 am
content: Before ordering large quantities of parts, it's always worth buying a few to test the circuit with those specific components. RS usually has most ICs / transistors in stock and you can buy them in low volume.For 15 bucks you can get 2 or 3 different micro controller boards to play around with. I'm not sure if you used STM 32, Pi Pico or ESP 32 before, but they're fun to play with.

author: DeadlyChemist
author_rank: Regular Contributor
timestamp: June 22, 2022, 01:56:04 pm
content: Quote from: OM222O on June 22, 2022, 10:21:48 amTrue, but i'd rather buy everything/too much than pay 18€ shipping/50€ total next timewould order 50 trannies, 2 references, 200 1R 1/2W resistors and some other stuff (more below)Quote from: OM222O on June 22, 2022, 10:21:48 amalready got some, also digikey is bloody expensivewhat i picked is random IR leds (diff wavelenght) not super accurate but crudy way to test what my camera can/cannot use as nightvision.also could you please check if this voltage reference is good enough (probably overkill)/easy to use?https://ww1.microchip.com/downloads/en/DeviceDoc/20005474E.pdfi assume i should grab some parts for "5.1.1 BASIC APPLICATION CIRCUIT"is there anything else i should add?

author: OM222O
author_rank: Frequent Contributor
timestamp: June 22, 2022, 09:09:57 pm
content: I have no idea what "5.1.1 BASIC APPLICATION CIRCUIT" isThe reference you chose is definitely good enough with 0.1% accuracy and 20mA drive capability

author: DeadlyChemist
author_rank: Regular Contributor
timestamp: June 22, 2022, 10:34:26 pm
content: Quote from: OM222O on June 22, 2022, 09:09:57 pmlook at the datasheet page 15.will also order 2.2µ and 300pf, ceramics, in big package (1206, 3216 metric) so it's even easier for me (both good brands)willl update here once i order and receive the parts, might run a test as wellthanks for the help !

author: DeadlyChemist
author_rank: Regular Contributor
timestamp: June 29, 2022, 11:40:47 pm
content: okay the parts from digikey arrived !so I don't want to make any drama or anything but holy sh*t that's a LOT of plasticAnyways: here is the rundown:FQD7N10LTMCT-ND - MOSFET N-CH 100V 5.8A DPAK (50)RNCP1206FTD1R00CT-ND - RES 1 OHM 1% 1/2W 1206 (200)MCP1501-10E/SN-ND - IC VREF SERIES 0.1% 8SOIC (got 2)1276-1072-1-ND - CAP CER 2.2UF 25V X7R 1206 (5)399-C1206C301J5GAC7800CT-ND - CAP CER 300PF 50V C0G/NP0 1206 (5)other orders:MCP 4461-103E/ST - digital pot quad channel 256 step (7)MC 33204 DG - op amp 4 channel SO-14 (15?)I did try a setup with 1 op-amp, 5v source, 10R resistor and no potentiometer, just some resistorsit did work, kinda?was very touchy, probably because of beeing on a breadboard and mid airalso the current wasn't right, at all, should have been 300mA was like 100mA, should be 600mA was like 250mAi assume this is because breadboard + no resistors/caps anywherehere the the plan:https://tinyurl.com/2d2zq6m7- simulation does not work anymore, but will be relevantbasically i would use EasyEDA to make the curcuit and later maybe @OM222O can help with the PCB because you guys know tricks, i don't... or maybe he can do both, that be appreciated, more belowthe led grid will be 4x4 and every led has 2 channelsbecause everything is quad channel (pot, op-amp)i assume the best is to fit 1 quad potentiometer which will control 8 leds, 2 zones x 2 colors x 2 ledsthis would give me current control over 2 leds at a timeif you imagine the grid beeing like this:11 12 13 1421 22 23 2431 32 33 3441 42 43 44also every number having W for warm and C or coldfirst board would allow me to control current to:11C + 12C (pair) (one pot, 2op amps, 1 follower)11W + 12W (pair) (one pot, 2op amps, 1 follower)13C + 14C (pair) (one pot, 2op amps, 1 follower)13W + 14W (pair) (one pot, 2op amps, 1 follower)i could split it from 2 to 1 or expand it from 2 to 4 (basically have 4 zones/rows)but if i split it, i need more digital pots (i only have 7 i think)and if i expand it to 4 to would be messier designor maybe we put the follower and potentiometer on the same board as arduino/raspi ? that would be even better now i think? and 1 board is 4 leds (instead of, so 11W, 11C, 12W, 12C and takes 2 signals/voltages 0 - 1.024vI dont know the best way, please let me know what's smartestanyways, please add/or let me know what and where caps/resistors for stability/stop oscilations from the opamps/followers as well as general stabilitythe mains (well, 24v) fuse will go in circuit without a board, but if you have ideas what to add on the board, let me know !i will also need a carrier board for the leds, but that will come laterdon't need the full pcb design now, just approx size/planscurrently my next step is getting the heatsinks, however im in a middle on moving 600kmthanks, this wouldn't be possible without your help ! (i will set up github and everything once im mostly done)

author: John B
author_rank: Frequent Contributor
timestamp: June 30, 2022, 02:44:26 am
content: I'm in the process of making something similar to you. I would echo some sentiments in that you should try to make a small batch of units (like 5 tops) and actually using them and testing them for a good while. I'm working on a lighting project, where I have about ~30 LED driver boards, ~20 LED driver PSU boards, ~20 microcontroller boards etc. I purchased a lot of components ahead of time (I was also mindful of the supply chain shortages) and then radically changed the design halfway, and while I have been able to reuse the vast majority of components, a lot of things like inductors, switchmode LED drivers, and capacitors aren't going to be used leaving me with a lot of money tied up in components I'm not sure I'll get around to using in a reasonable time frame.Also have you looked into automated assembly? I am hand soldering, and have literally thousands of components to solder, lol FML. I would have looked into partial automated assembly. It would have been a massive help even just to do the cheap resistors and caps.

author: DeadlyChemist
author_rank: Regular Contributor
timestamp: June 30, 2022, 02:36:46 pm
content: Quote from: John B on June 30, 2022, 02:44:26 amexpensive + i actually enjoy soldering, it's a nice activity to have while having some beer and youtubeso most likely i'll do everything by myselffor now i need a final design/schematic with all the stuff (please help)meanwhile im working on getting money for the heatsink (+ making the actual heatsink, yikes...)but again, i'm in middle of moving right now, so the project is going slow...

author: OM222O
author_rank: Frequent Contributor
timestamp: June 30, 2022, 04:51:18 pm
content: The current not being what you expect is a very good sign that the op amp that is driving the mosfet is oscilalting. I'm away from home now so can't give detailed inatructions on how to fix it, but a simple test would be adding a 100 ohm resistor between the output of the op amp and the mosfet gate. If that doesn't fix it, 2 resistors and 1 capacitor should do the job. I'll post that tomorrow when I have time.Edit: something like this usually fixes even the worst oscillations:https://electronics.stackexchange.com/questions/162351/why-is-my-op-amp-oscillatingIf this doesn't fix the issue then the mosfets don't have enough "gain" ( I think it's called trans conductance). I'm pretty sure I checked the fets current capability at 5v Vgs, but I'll double check later.Edit 2: how did you calculate the current? 10R and 5V is a max of 500m, so 600 is impossible even with no load 🤔 I'd double check that

author: DeadlyChemist
author_rank: Regular Contributor
timestamp: June 30, 2022, 09:17:17 pm
content: Quote from: OM222O on June 30, 2022, 04:51:18 pmtried 3.3v, 5v and also other resistances, so my math was correct i hope lolQuote from: OM222O on June 30, 2022, 04:51:18 pmthe voltage is 1v from reference remember? 4 ohms 1 volt?i wont be able to test anything in the next ugh, 2 months?but yeah, might even go straight to PCB, does not cost THAT muchas for oscilations, might take the fix anyways, because i dont wanna find out that it's oscilates at some weird frequency or whatever, i'll chuck a cap wherever i can tbhjust tell me what extra to get

author: OM222O
author_rank: Frequent Contributor
timestamp: June 30, 2022, 09:27:18 pm
content: Quote from: DeadlyChemist on June 29, 2022, 11:40:47 pmif you put 5v directly across a 10R resistor (ignore MOSFETs or other things) you can have a maximum of 500mA, that's just ohms law!to calculate current you should divide whatever voltage is at the non-inverting pin (+) of the op-amp by the current sensing resistor.DO NOT order PCBs if you don't have a working circuit, trust me on that one. if you're worried about the breadboard causing issues, solder the components with short wires (for SMD parts you can buy breakout boards similar to this:https://www.ebay.co.uk/itm/362262676455)also, your simulation is broken because of the voltage reference you added. I'm not sure how you created the model for it, but the error says there is a wire loop somewhere (most likely connecting the grounds together with no resistor). If you remove it, the sim runs fine.Edit: If you can give me a schematic of exactly what you tried, that would be helpful.The only extra components you will need to solve oscillations are resistors and capacitors (I assume you have some common values on hand to test, for example, 100ohm, 1kohm, and 100nF). If you really want to jump straight to PCB design, it's a good idea to include the extra components and not populate them later on.

author: DeadlyChemist
author_rank: Regular Contributor
timestamp: June 30, 2022, 11:32:21 pm
content: Quote from: OM222O on June 30, 2022, 09:27:18 pmi have tried other resistances than 10 ohms as well (said it above?), i did put 2 and 3 10 ohm resistors together, but anyways...Quote from: OM222O on June 30, 2022, 09:27:18 pmgot some, might try that, would need to buy some wires first or might just cut up old lan cableQuote from: OM222O on June 30, 2022, 09:27:18 pmwill probably re-test everything, the test was very quick and dirty, veeery unoptimal, i do have a picture i took, but not sure you can make anything out lol, tbh, better don't look, you'll question your life, my work-bench is full of boxeshttps://cdn.discordapp.com/attachments/718850705363828748/991711381621583962/20220629_162635.jpgQuote from: OM222O on June 30, 2022, 09:27:18 pmi actually dont, resistors i do, but i have no caps, i usually just order them as i need them or desolder from junk (because i dont make things like you all, i fix/mod things once a while)actually found 2x 220µF capsthe pcb would probably just be a final testbecause whatever we come up with, i dont believe the first prototype will be the actual PCB i'll use lol

author: OM222O
author_rank: Frequent Contributor
timestamp: June 30, 2022, 11:49:25 pm
content: one problem you'll have is that the digital pots ICs you bought have a 2 bit address (A0 and A1 pins), meaning you can only have 4 of them on a I2C bus (total of 16 actual pots because each single chip has 4 pots). What MCU are you using? does it have multiple I2C ports or do you have to use 2 MCUs as well?I can start designing the schematics tomorrow as well.

author: DeadlyChemist
author_rank: Regular Contributor
timestamp: July 01, 2022, 12:15:03 am
content: Quote from: OM222O on June 30, 2022, 11:49:25 pmthought of that, there is a i2c multiplexer, would use thatyeah, if you know where to add fuses/protection/anything, that be nice, so far i only thought of 24v input fuse, but nothing elsefor mcu, im most likely gonna use Raspberry Pi Pico W (launched today hehe) high overkill, but for 6€ you can't beat itEDIT: the dev time in python would be minimal, so i like it

author: alligatorblues
author_rank: Regular Contributor
timestamp: July 01, 2022, 04:56:58 am
content: Wow, all this work. I wanted to build some studio lights. I purchased five 100W square led arrays about 1.5" square, maybe 16x16 leds. I purchased the drivers from the same seller, which were 12VDC to 40VDC converters enclosed. I took some heat sink fan cpu coolers, tapped some holes and affixed the leds to them with acrtic silver thermal paste interface and 2 screws! I took some wallwarts I had laying around for the 12VDC IN, and cut off one side of (4) PC PSU cords.I soldered the cord leads to the prongs on the wall warts. So, now they plug into the wall! I made 4 lights, three 100W and 1 200W. I think the brightness of leds compared to incandscent is about 25:1 per W. So, the 100W are equivalent to about 2,500W incandescent, and the 200W about 5,000W incandescent! So, I required a dimmer, because these things are surreal they're so bright!I just used a variac I had laying around for a dimmer, and it works pretty well. So, I think my total bill was ab out 150.00USD because I had a lot of little stuff I needed already! My basement is a electronics salvage yard. There's some pretty good stuff in there too! If I was disciplined enough to sell it all I'd probably make 50,000.00USD!But I've got plans for almost everything down there! I just picked up a ESI SR104 10k resistor, Fluke 732B DC STANDARD, (2) 10Mhz. rubidium standards, 6 HP 735A 1.0VDC Standards with +-0-1000uV by 1.0uV control, 2 HP 34401A 6.5 DIGIT DMMs, Fluke 8842A DMM, and a huge box of miscellaneous passives, actives, and I don't know what all else, for a C-NOTE, at a yard sale. The lady was older than dirt! Her husband had just died. And, she was having a sale to downsize.The husband had been in electronics somehow, and she was really thankful for all the work I did carrying all the stuff to my UTE, all by myself! Always carry cash. She wanted cash! I said, all I have is a $100 bill. She said, Oh, I cwn give you change back! I said, No, you've just had a significant loss in life! You can just keep the whole thing. She said, Oh, Bless your heart!So, now I've got a little project testing that stuff. Oh, and there were (2) 10A Staco variacs, and a bunch of leads.It pays to shop yard sales. She thought she was going to have to leave the stuff at the curb for collection, because no one else even looked at any of it!So, anyway, that's the story of 9500k studio lights. They just get a little warm. So, the fans on the heatsinks must help a lot.

author: DeadlyChemist
author_rank: Regular Contributor
timestamp: July 01, 2022, 12:09:55 pm
content: Quote from: alligatorblues on July 01, 2022, 04:56:58 amthe light quality will be eh, but depends what you doingas for flicker, this will definetly flicker, set your camera fps as higha s you can, and lower the shutter speed as low as you canQuote from: alligatorblues on July 01, 2022, 04:56:58 amUSA i guessthe best things i bought at a "yard sale" basically we have a flohmarkt (german) every couple of months... you go, rent a spot and offer to sell your junkso best things i bought were 6 mercury thermometers (some high temperature) for like 10€no one here makes yard sales like in movies/youtube flip series

author: DeadlyChemist
author_rank: Regular Contributor
timestamp: July 03, 2022, 09:49:16 pm
content: did some math and thinkingaccuracy:my resistors are this:https://www.digikey.de/de/products/detail/stackpole-electronics-inc/RNCP1206FTD1R00/22403021 OHM 1% 1/2W 1206 so 4 of them (ignoring gaussian distribution) would be 3.96- 4.04and my transistorhttps://www.digikey.de/de/products/detail/onsemi/FQD7N10LTM/1053477has a resistance of 0.275(typ) to 0.350(max) sadly does not say minimum, but i can just assume 0.200so basically 0.200to 0.350(check if im correct)together that would be maximum of 4.16- 4.39worst case possibleputting that into simulation gives me 246.133mA - 233.238mA basically 5.53% difference, considering everything is gonna be at very similar temperature, from the same box and datasheet values are usually in typ range instead of min/max everything should be within 2% or so which is pretty good, but 5% is also fine, i assume the leds will also have some variation.Current measurment:thinking to integrate this or similarhttps://www.aliexpress.com/item/1005003671166977.html?ina3221 tripple current sensor "Up to ±1.638A current measurement"basically could split warm and cold and get some proportions/feedback, could be useful, they cost pennies and Rpi Pico W has few pins i can dedicate to that (or do you know of a better chip?)but because it's "upto 1.63A" and i don't trust aliexpress so 4 channels/1 input (4x 250mA) x3 boards to get upto 36 ledsone board is like 3€ so might include itother features:I'm looking to detect the power switch (230V) beeing turned on and off quickly, basically some leds have the feature that if you double tap the power switch you get another mode, im looking to implement that, any ideas?I'm unable to test anything so currently just looking thru things i can implement

author: OM222O
author_rank: Frequent Contributor
timestamp: July 04, 2022, 12:21:25 pm
content: The resistance of the MOSFETs doesn't change the accuracy, only the voltage reference, the input offset voltage of the op-amp, and the resistor value determine the output current.Current measurement shouldn't be necessary, as long as the circuit is verified to work correctly, then whatever you set in the software, is what you get on the output. It could be useful for fault detection and protection if somehow the MOSFET fails short, but adds a lot of costs.If you really want to monitor the current, there are tons of I2C chips available, just need to find one that has enough gain to read the small currents you're working with. I can have a look if you want. This uses 0 extra pins which should be ideal for your situation. If you want to search for yourself, you can have a look here:https://www.ti.com/amplifier-circuit/current-sense/power-current-monitors/products.htmlI'm not sure how they do it in commercial lights, but there are many methods for detecting a double press. I think the easiest solution is to add some sort of backup power (probably super capacitors + boost converter). Then you need to monitor the "high voltage side" (probably monitor the 24v output of the PSU rather than 230v mains) with a comparator of some sort. If the high side voltage drops below the output of the boost converter, then you know the switch has been turned off. Then you can write the logic for what happens after power down / power up.

author: DeadlyChemist
author_rank: Regular Contributor
timestamp: July 04, 2022, 03:01:43 pm
content: Quote from: OM222O on July 04, 2022, 12:21:25 pmyeah, i think the aliexpress listing i showed above with ina3221 should be perfect tbh, the board is already made, and it's cheap enough.. unless you have better idea?, surely the alie board will be crappy quality but should be fine.Quote from: OM222O on July 04, 2022, 12:21:25 pmyeah, but what if the leds are really low power, i flick off-on the switch, but the caps in the psu/boards still are basically supplying the power, so it won't detect anything im worried...https://www.aliexpress.com/item/1005003739343987.html?i dont know what it outputs, but maybe have the micro powered by big cap with diode or something, and use that to detect if main power is on or off or even secondary chip/comparator ? or instead just put a hall effect sensor next to the main wire?i prefer to deal with 230V instead of 24v in this case, because it should be more reliable

author: OM222O
author_rank: Frequent Contributor
timestamp: July 04, 2022, 04:50:01 pm
content: those modules have a ton of extra components that you don't need and add a sense resistor that you already have. If you want to use a current sense amplifier, the best bet would be to buy the IC rather than a module.those current clamps are way too much of an overkill (definitely not used in commercial circuits), but they do work. If you have one of the commercial units that do this, might be a good idea to take it apart and reverse engineer it, but I have to question the use of this though, especially the fact that you mentioned using the Pico W. Why not host a small web page on the Pico to change the settings/mode etc. ?Edit: if the current is low (LEDs on very low brightness), the current clamps will also have trouble detecting it. I still think it's best to monitor the voltage of the PSU and see when it drops below let's say 20v or 22v or something similar. With any reasonable load, time taken for the output voltage to drop from 24v to something below that should be small enough that it'll be detectable.

author: DeadlyChemist
author_rank: Regular Contributor
timestamp: July 04, 2022, 07:58:35 pm
content: Quote from: OM222O on July 04, 2022, 04:50:01 pmtrue, but then how much would it cost to add 32 current measurments? because if im gonna use the 4R as current shunt, i have 32 of them?Quote from: OM222O on July 04, 2022, 04:50:01 pmi'll have that as well, but since i'm adding RGBYWU leds as well (havent bothered about it at all for now)RGB for accent with white/RGB party lol?White for well, not usedYellow (kinda monochromatic) for accent or generally just yellow for that low pressure sodium lamp look, or if i want to work with film/light sensitive stuffUv (405nm, safe) for party mode i guess? or when i would firm some glow in the dark stuff, could be usefulAlso to anwser the question:i want to add "sleep mode" basically double hit the switch, the leds turn on very low on Red (because red does not kill human nighvision apperantly) and after a minute or whatever but still beeing on, so i can turn in on from my phone/clapping?/whateveror maybe double cycle (so 4 clicks) to get into safe mode so, yellow only untill changed in settings or whatever, honestly, not 100% sure, but having the ability is soo usefulQuote from: OM222O on July 04, 2022, 04:50:01 pmfair, but i could just use the like power lines detector that goes thru walls and looks for active cables, some meters have it built inbasically this, whatever you call ithttps://www.aliexpress.com/item/33036736656.html?might be overkill on the stuff i wanna add/implement even if i don't end up using them, but having possibilities is nice

author: OM222O
author_rank: Frequent Contributor
timestamp: July 04, 2022, 09:20:02 pm
content: those probes use a very high gain amplifier to detect ANY electric/magnetic fields, won't give you a good measurement of how much current is in the wire (few pA or uA as leakage vs few mA for a device that's turned on). Again, I really don't know how they do it in commercial units, so if you really want this feature, you may wanna reverse engineer one.Funny enough I had a look at TI'sparts and the ina3221 is the only part that can monitor 3 lines at once, but even in massive quantities (10k+ parts) it still costs around 1.5 pounds, but the module you showed is only 1.7! I have no idea how that is possible unless they're using fake ICs? I still don't think you need current monitoring. Even if the MOSFET fails short, you will only have (24-22v) / 4which is 500mA. This can be easily detected with a comparator since you said the max current you plan to use is less than 300. This will be much cheaper and require no programming. If you bought extra op-amps, you can use them as comparators, if not, comparators are dirt cheap these days.Either way, I think you need to think about those features later on. let's focus on the actual circuit first.

author: DeadlyChemist
author_rank: Regular Contributor
timestamp: July 04, 2022, 10:25:25 pm
content: Quote from: OM222O on July 04, 2022, 09:20:02 pmmost likely and fair enough.

author: OM222O
author_rank: Frequent Contributor
timestamp: July 05, 2022, 05:58:24 pm
content: I actually remembered that I made a very similar thing about 3 years ago for a robotics competition. I've put it up on wordpress and as you can see, I did include two 1k resistors and a 100nF capacitor to stop the op-amp oscillation. The brightness change isn't super visible on the camera (only visible when the LED has low intensity).https://manisprojects.wordpress.com/2022/07/03/eurobot-lighthouse/I've been really busy so haven't had time to start a new design for you, but I think I'll have time after this week. Other than using a digital pot instead of a manual one, I think the rest can be copied without any changes. let me know if there's anything else you want to add (other than current sensing).

author: DeadlyChemist
author_rank: Regular Contributor
timestamp: July 05, 2022, 10:00:36 pm
content: Quote from: OM222O on July 05, 2022, 05:58:24 pmdamm, that's a nice thing !Quote from: OM222O on July 05, 2022, 05:58:24 pmno rush, i basically only want to get the "driver" pcb/design done so op amps, maybe pots, transistors, etcthe board and final schematic with the micro, sensors and whatever else i come up with and or voltage reference? i'll do probably after i assembled the drivers and tested everything.also can't think of anything (except sensors) to add that changes the designso i think making the drivers is the first step i guess?

author: OM222O
author_rank: Frequent Contributor
timestamp: July 10, 2022, 02:32:59 pm
content: I have started designing the schematic and PCB for the project:https://oshwlab.com/theepicn008/eevblog-cc-led-driverA really neat solution would be to have a stackable design where the control board sits at the top and provides the 1.024V reference to the driver modules and you can stack the driver modules on the bottom (you can stack up to 4 driver boards (16 output channels) because of the I2C address issues). If you have an I2C multiplexer let me know; It can be included in the control board.

author: DeadlyChemist
author_rank: Regular Contributor
timestamp: July 21, 2022, 02:25:51 pm
content: My health is back (ish)Quote from: OM222O on July 10, 2022, 02:32:59 pmI took a look at the schematic and looks like basically a done driver board, good jobShould I make an account there so you can add me? or how does that work? later in the build process i'm looking to dump images/videos/stuff on there so it's more or less easy to reproduce, always used github for that stuff, but i guess that website works as well.Quote from: OM222O on July 10, 2022, 02:32:59 pmthe multiplexer would behttps://www.adafruit.com/product/2717or similar TCA9548A based one (they cost 3-5€ on ebay)yeah i guess that's the best flow, not sure if "stackable" like litteraly, is what I want (because im worried the stack might cause a shadow + heat buildup), but yeah, 4x driver board and 1 main board or so. what size are we even talking for the driver board? i prefer a long skinny one so i can put it on the edges.The main board (layout) is last worry for now until i test it and do the heatsinkI began writing driver (made 0 progress, but technically began) for the 4 channel digital potentiometer in micropython. I'll update once a while if i'm stuck/doneWill also buy a large piece of paper and draw the heatsink/leds/whole layout (can't find software that does not suck)most likely will do with 400x400 heatsink (16x 10x10 heatsink) i only technically need 300x300 but meh

author: OM222O
author_rank: Frequent Contributor
timestamp: July 22, 2022, 07:46:13 pm
content: I meant literally stackable. 1 control board, 8 driver boards. Heat won't be an issue as you can use a fan to blow fresh air on the stack (highly doubt that'll be required) and what do you mean by shadow? the board will be placed above the light fixture (aluminum angles/plate). Do you have drawings / 3D models of what the final fixture would look like? that'd be helpful.Driver boards are not completely finished as I still need to add comparators, a latch circuit, and P channel MOSFETs to disconnect the 24v input in case of overcurrent detection.For the digital pot, I have never used that specific IC but had to write my own library for a similar microchip pot, let me know if you need help.other than that, I think I can start designing the control board as well.To join the projects, you need to create an account on easyeda.com and send me your email/user ID so I can add you.

author: DeadlyChemist
author_rank: Regular Contributor
timestamp: July 23, 2022, 12:41:20 am
content: Quote from: OM222O on July 22, 2022, 07:46:13 pmi have 2 plans in my head for mounting/heathttps://prnt.sc/JugNYgPaiaATorhttps://prnt.sc/Fx0IrxL2DE3Gfirst of all, i don't want any fans, i did the math, and a 3x3 grid of heatsinks (100x100x15) (green) with 4x4 grid of warm-cold leds should be enough to keep them under 60Cthe red would be the electronics and blue would be RGBYWV leds (i just briefly talked about), i have 5 or 6 of them, and not sure of the locations, might go with more, not sure as of now, will worry later as the voltages are unlucky, not super good with 24v, lots of energy to burnthe 2nd plan would be to super overspec and make it bigger, what i like, the price would be 50€ vs 100€ for heatsinks (9 vs 16)the heatsinks would be in 4x4 grid and everything should be ice cold basically (most likely will go with that, even tho it's wasteful)but it should be basically like a tank that can disappate a lot of poweri spent about 2 days looking for cheapest, best heatsinks for this project (30cm - 50cm) and welding up 10cm heatsinks is sadly the best way i foundthe 24v powersupply will be externalwill prob mount it 3-6cm from the ceilling to have airflow/convection (should be enough) using a bracket or something.the "case" for the light will be just a square of stainless steel with a frosted plexiglass mounted to it, not sure, spent many days looking at existing designs and don't like a single one (suggestions open)the light will be super thicc and ugly (well, i think stainless looks nice) but that was never the goal.Quote from: OM222O on July 22, 2022, 07:46:13 pmwill do, might take me few days (moving and stuff)also have done 0 experiments regarding light uniformity, like how far away the led needs to be from the frosted glass to look uniform, also how close the leds need to be to each otheri guess once i built the driver i can just experiment with 4 leds and see what looks howthe 4x4 heatsink might put the leds too far apart i'm worried, i'm not sure how to calculate that without actually testinghere is my terrible explanation of the shadow im worried abouthttps://prnt.sc/2spWGymy4zcubasically, let's say the electronics stack is whiteand red would be the frosted glas, i'm worried that the light might hit the electronics on a weird angle where one side/corner is just slightly dimmer than the other ones, basically less uniformyeah, i'm probably just paranoid, but i feel like placing the electronics all around is better than i 1 place anywaysunless you have a better design/idea

author: OM222O
author_rank: Frequent Contributor
timestamp: July 23, 2022, 01:35:08 am
content: hmmm ... it is possible to design the modules to be daisy chained sideways instead of stackable on top of each other, but due to the increased distance, there might be a lot of noise/error in the 1.024v reference, especially on the furthest modules. adding capacitors can somewhat overcome that, but it's not ideal. Since you are so unsure about the final dimensions/design, I think it'd be a good idea to order some prototype PCBs and once you were happy with the test results, finalize the PCBs, but that requires desoldering parts from the prototype which can be a bit annoying.Do you have access to fusion360 or other cad packages (Solidworks, etc.)?For the RGB LEDs, you can add extra resistors to dissipate the heat without overloading the MOSFETs. since you bought a lot of extra 1 ohm resistors, this can be a nice solution.

author: DeadlyChemist
author_rank: Regular Contributor
timestamp: July 23, 2022, 12:07:45 pm
content: Quote from: OM222O on July 23, 2022, 01:35:08 amdont have hot air, buying isn't a problem but space is, so currently can't really desolder SMDi'm not that worried about reference, i can just run more individual wires to it instead of daisy chaining, but then you probably know betterQuote from: OM222O on July 23, 2022, 01:35:08 ami have autodesk fusion360 but im very terrible in it (can't get anything done)so i have been using blender for everything (including modifiying 3d prints...) but it's not ideal for accurate parts as you knowQuote from: OM222O on July 23, 2022, 01:35:08 amprobably, but again, first i need to buy one and test the actual voltage/current like i did with the white ones

author: OM222O
author_rank: Frequent Contributor
timestamp: July 24, 2022, 01:20:10 pm
content: You will ABSOLUTELY need to buy a hot air station for this project. Soldering that many SMD parts by hand is both very slow and unreliable (high chance of bad joints).I'll leave the PCB design for the end since you don't even know the physical dimensions of what you're trying to build. I made a customizable fustion360 light fixture which you can make from 4 angled pieces (any specific reasons for choosing stainless? aluminum is both cheaper and easier to weld. Anodized aluminum also looks better in my opinion):the frosted glass sits on top of the metal (I recommend adding some sort of foam or felt under it. You can easily buy self-adhesive foam tape in different sizes) and you can add a layer of light diffuser sheet+ fresnel lens (common construction in most LCD panels to make the backlight look uniform).Finally, the LEDs + heat sinks sit on top of that assembly with a bit of distance (using some sort of spacer, probably wood or 3d printed). Do you know how you want to mount it to the ceiling?Edit: I personally bought a YIHUA 862D+ from amazon for about 60 GPB and have been pretty happy with it, I'm sure you can find similar cheap soldering stations if you have a look.

author: DeadlyChemist
author_rank: Regular Contributor
timestamp: July 24, 2022, 03:37:50 pm
content: Quote from: OM222O on July 24, 2022, 01:20:10 pmhm, probably will get the same one, heard great things about it somewherebut will solder bulk by hand anyways, it's relaxing for me to solder for hours and hours, hotair is meh, not satysfying and loudonly worried about reliability tho, as hotair is just better i agreeQuote from: OM222O on July 24, 2022, 01:20:10 pmmy friend can weld whichever material i want, and stainless feels premium?, might go with aluminium but for now it does not matter that muchi would go with bright pink anodized aluminium but sadly it would cast a pink cast on everything + welding anodized isn't really possibleQuote from: OM222O on July 24, 2022, 01:20:10 pmlooks good i guessfoam is easy to get, but don't get why i need it in the first place? is direct contact bad? (there wont be any shaking or anything)no clue where i would get fresnel lens or difuser sheet, except broken tv's or something? but that's not really repeatableQuote from: OM222O on July 24, 2022, 01:20:10 pmi thought the "frame" will have hooks (L bracket or whatever) on top to mount to the big heatsink, so basically the frame will be a spacer?as for mounting to the ceiling?, no idea, my plan was to go to a hardware store, look at the parts/what exists and figure something outunless you have a "ready" solutionalso great job on the 3d cad model, i would have need weeks for it, days in blender...

author: OM222O
author_rank: Frequent Contributor
timestamp: July 24, 2022, 04:14:04 pm
content: Quote from: DeadlyChemist on July 24, 2022, 03:37:50 pmYou first weld it into shape and then anodize it.Quote from: DeadlyChemist on July 24, 2022, 03:37:50 pmI personally don't like the idea of glass on metal (too many broken PC side panels and those are tempered glass), but if you're ok with it, then just leave that part out.Diffuser sheets are pretty common in photographing industry, you can buy huge sheets for relatively cheap:https://www.amazon.co.uk/Diffuser-Diffusion-Seamless-Modifier-Photography/dp/B085FRNY1Hsame with fresnel lenses:https://www.amazon.co.uk/DarwinUK-Large-Rigid-Fresnel-395mm/dp/B01MU4HR20or like you said, you can take apart old broken TVs.Quote from: DeadlyChemist on July 24, 2022, 03:37:50 pmusing L brackets sounds like a good idea, but then you need to figure out a way for mounting the heat sink to the ceiling.I think the first step is to figure out exactly how many LED modules you want to use and in what configuration (4x4 only white? larger array with RGB?) and the final spacing and dimensions of the LEDs. This lets you finalize the dimensions of the frame and tells you how many driver boards you will need. I still think a stackable design works much better if you're willing to mount the frame a bit further from the ceiling (maximum of about 10cm if I had to guess). All the electronics will be mounted above the heat sink (you can just use double-sided tape if you want something easy or you can 3D print a small enclosure for it if you want to be more professional).Let me know when you decided on the LED arrays and their spacing.

author: DeadlyChemist
author_rank: Regular Contributor
timestamp: July 24, 2022, 05:43:32 pm
content: Quote from: OM222O on July 24, 2022, 04:14:04 pmthanks for the linkQuote from: OM222O on July 24, 2022, 04:14:04 pm4x4 (16) of thishttps://www.aliexpress.com/item/1005003210480731.html?(white)the spacing, im unsure what looks good on a 400x400 grid (more below)as for thishttps://www.aliexpress.com/item/1005001267331243.html?i can see the voltage range is 2.2V - 3.6V so technically i can fit 6 to get 21,6V (but i haven't tested the leds at all so i don't know) the current is 500mA but i'll go with tiny bit less (-50mA?) so maybe 7 leds can be fit into 24V?i know the RGBWYV are crappy quality but that's fine. i only really care about yellow and redI'll have to buy 10 of them for 50€ but oh well, unless you know of an EASY way how to use like 10 of them? without making my lamp into a bigger space heater than it already isalso i dont know where/how to fit 6-7 or all 10 leds into a 4x4 grid that look nicelyThe heatsink will be thishttps://www.conrad.de/de/p/fischer-elektronik-sk-81-100-sa-strangkuehlkoerper-2-k-w-l-x-b-x-h-100-x-100-x-15-mm-188557.html(can't find anything better/cheaper)in a 4x4 array welded together (400mm x 400mm x 15mm) i think they are anodized, but one acid bath is enough.my friend can weld aluminium, worst case i'll use brazing rods and a dozen of gas burners.I'm still thinking of mounting the electronics on top as you said. with 400x400 heatsink it should be plenty enough cooling and space

author: OM222O
author_rank: Frequent Contributor
timestamp: July 24, 2022, 08:10:43 pm
content: the easiest way to deal with 10 is to break them into two groups of 5 LEDs, but since these are small COB modules, I think you can always add them later. Let's focus on the 4x4 white LEDs for now.You don't need to weld the heat sinks together; it's easier to weld some straight pieces of steel/aluminum (whatever the frame material is) to the top of the frame. You can then drill some holes and screw the heat sinks onto those bars. This way you won't need extra L brackets either (bars act as L brackets). Then you can use 1 heat sink per LED (400x400mm) which should be enough cooling. I'll post an update when I finish the design.

author: OM222O
author_rank: Frequent Contributor
timestamp: July 24, 2022, 09:28:30 pm
content: Mechanical design is mostly finished:https://a360.co/3BbbbPLyou just need to finalize the dimensions of the angle pieces and the bars on top.It might be a pain in the ass to drill that many holes, especially in the heat sinks (you can ignore the unused holes on the left and right-hand sides. They're there because I wanted to copy the bar 5 times).You also need to tap the heat sink holes which is not ideal. Are you sure you can't find a larger heat sink?I'm not sure how efficient the LEDs are but tbh this seems a bit overkill. If you can measure their maximum heat output, you may find that using a 400x400mm aluminum plate is enough. If it wasn't enough, maybe adding a few heat sinks to the plate could be enough (I can't imagine you'd need more than 4 heat sinks total).Edit: I just realized I'm an idiot ... it would be impossible to put the glass in with this design. But it should be fixed now (I added 2 more bars that can be screwed to the frame with some L brackets. The 5 support bars can then be welded onto those 2). I still think you should reconsider using 16 heat sinks though.What I mean is that instead of having the 5 supporting bars, you can have a 400x400mm aluminum plate (around 3mm thick) as a heat spreader. If this surface area wasn't enough, then you can use thermal adhesive to glue heat sinks to the plate. If you can figure out the efficiency of the LEDs or measure how many watts of heat each one outputs at 250mA, then you can even simulate it without spending any money.

author: DeadlyChemist
author_rank: Regular Contributor
timestamp: July 25, 2022, 01:32:03 pm
content: Quote from: OM222O on July 24, 2022, 09:28:30 pmi can't or they get ridiculessly expensive, plate idea belowQuote from: OM222O on July 24, 2022, 09:28:30 pmbasically the math i did was:the max power cool white can use would be 16*7*0.85 basically 16 leds at 7W at 85% max power (255mA instead of 300mA) about 95.2Wfor warm white it's also 95.2Wrbgwyu would be 6*18W (worst case, everything turned on)so total is about 300W, assuming 0% efficiency of the led, that's 300W i need to get rid ofthe heatsinks are 2K/Wusing 16 of them, that's 0.125K/W at 300W that's about delta 37.5Kso the heatsink would rise by about 37.5C with EVERYTHING turned on with 0% efficiencyleds have actual efficiency of about 30%, 30% is light, 70% is heatso that's about delta 26.25C with a room temp of 25C thats a chilly 50C at 300W i'll probably never use lolmy goal is under 60C at about 200W (140W if you count 30% efficiency)so 3x3 heatsink grid could defiently workI like the 400x400 heat spreader with few heatsinks at the back, but i can't really do any math on that, how much can that handle? on ebay 400x400x3 aluminium plate is about 25€ plus like 5-10€ for shippingway cheaper than 120€ + work for a heatsink, but i have no clue how much it can handle.I defiently prefer a big plate, but need some help regarding thermal capabilityas for taping the holes, that's fineI'm thinking to go the "smart" way and mount the leds on a small carrier pcb (alumiunium) which gets screwed into the heatsink with some thermal paste inbetween (thermal glue between the led and board)this is worse thermal contact than direct led on heatsink, but the cleanup/replacement is way easierim unsure, might go lazy and just mount them without carrier board.

author: OM222O
author_rank: Frequent Contributor
timestamp: July 25, 2022, 02:52:15 pm
content: I found this:https://www.heatsinkcalculator.com/flat-plate-heat-sink-calculator.htmlA single large plate won't be enough as I guessed (doing the math for 1 LED: 100x100x3m flat plate gives a thermal resistance of 7.84°C/W which at 10 watts and 25c ambient is around 100c).I suspect adding 4 or 6 heat sinks to the plate should keep it below 60c, but it's hard to tell given how much of it is guesswork (thermal paste thickness, conductivity, etc.)Do you really need a 300-watt LED panel? that seems a bit too much for any indoor application.If you wanna be sure, go with the 16 heat sinks, but it's gonna be painful (and you'll need a drill press, calipers, and taps which I assume you have access to).You may also want to reconsider using fans because there is too much heat in a small area.Edit: I'm gonna do a proper simulation in fusion later when I have time.Can you take some pictures of the COB module from the top, side, and bottom next to a ruler? the aliexpress listing shows different packages which is confusing.

author: DeadlyChemist
author_rank: Regular Contributor
timestamp: July 25, 2022, 05:30:10 pm
content: Quote from: OM222O on July 25, 2022, 02:52:15 pmyeah no, 6 heatsinks are about 6*7=42€ + 5€ shipping plus 25€ plate + 10€ shippingthats 77€i'd rather pay 16*7€ = 112€ + free shipping for 16 heatsinksQuote from: OM222O on July 25, 2022, 02:52:15 pm300W is simply ridiculess, agreed, but could be very useful for slow motionbut it's technically 100W warm 100W cold, 100W rgbwyuas for heatsinks, i intended to give my friend just the 16 heatsinks and tell him to have fun welding it all up lol + would have a big solid heatsinkbut the connectors/straps sound also good, i don't mind doing it myselfas for fans, no, to much space (simply thiccness) and I hate any noise (even the barely audiable one)Quote from: OM222O on July 25, 2022, 02:52:15 pmThanks, and I'll next week once i unpacked some of my stuff from boxes

author: OM222O
author_rank: Frequent Contributor
timestamp: July 25, 2022, 09:42:11 pm
content: I ran a simulation using the plate and heat sinks with convection and emission:I really doubt this is correct though ... I have to investigate a bit more (need a more detailed model of the LEDs; right now they are 13mm aluminum cylinders) and remove the heat sinks to see if the temperature goes up or if I messed something up.Again, just based on pure guess I'd say a large plate and 4 heat sinks should be enough cooling and much easier than stripping paint from heat sinks and welding them together. I'll post another update when I make sure the simulation results are correctEdit: I figured out what I did wrong. For heat load, I used 10 watts (14 watts LED at 30% efficiency) and selected all the LEDs thinking it applies 10 watts per LED, but fusion meant total power. After increasing it to 160 watts (10*16) this is what I get:This is assuming perfect transfer between the LEDs and plate to heat sinks (no thermal interface material / assume the entire thing is machined from a solid piece)4 heat sinks were definitely a no-go. Funny enough increasing them to 9 didn't improve things by a huge margin:The inner LEDs are just on the edge but the outermost LEDs seem to be fine. Now if we add the thermal paste inefficiencies back into the equation, even 9 heat sinks won't be enough.Edit 2: I have some bad news for you: after playing around with the simulation and using BOTH the heat spreader plate AND 16 heat sinks, the LEDs are at 50c with an ambient of 25c (25c delta). Again this is assuming no thermal paste (perfect transfer) so in reality, they'll be right around the 60C mark. Unless you want to run the LEDs at a lower power level, this design is very impractical on its own (ignoring RGB). If you want, you can send me your fusion 360 account so I can add you to the project to play around with the model yourself (everything is parametric and easy to change).I'm not sure how they measured the 2K/W (maybe with a decent amount of airflow?), but 16 heat sinks will definitely not be enough on their own. Increasing the convection value from 10 to 100 (aka using a fan) does improve things a lot but you said you don't want to do that.As a side note: heat sinks are extruded aluminum so you may not be able to easily find them wider than 100mm, but I'm sure you should be able to get longer ones (for example 100x500mm). Try contacting the seller to see if they can send you longer pieces (without cutting them down to 100mm).Edit 3: using the spreader plate and 4 heat sinks + airflow (fans) results in a max temp of 46c which is only 10c warmer than using 16 heat sinks! Increasing the plate thickness from 3 to 5 drops temps by another 3 or 4 degrees! This should tell you that the heat sinks you chose are a very bad choice for passive cooling and when using fans, just 4 should be enough.As you can see the innermost LEDs get a bit hotter than the outermost LEDs so you might want to run them at a bit lower power which is easy as you have full control over each individual LED from the driver board (it's a good idea to actually check the temperatures using a thermocouple after you build the whole thing).You can also watch this video :where they add a "massive" (compared to what's already in the steam deck) heat sink, but after about 30 mins, it reaches the same temperature as it did without the heat sink! but adding a small fan makes a huge difference in the end so they decide to keep the fan on there.

author: DeadlyChemist
author_rank: Regular Contributor
timestamp: August 02, 2022, 04:29:37 pm
content: Quote from: OM222O on July 25, 2022, 09:42:11 pmmy leds will be pairs (1 pot for 2 leds (2x cool or 2x warm)Quote from: OM222O on July 25, 2022, 09:42:11 pmI know that, but heatsink should radiate some power passively, the heatpipe just redirects the heatQuote from: OM222O on July 25, 2022, 09:42:11 pmi assume with fan it's gonna be way less than 2C per wattand yes, i don't want fanshere are the measurments:Im considering adding a tiny tiny fan and use software to ramp it up barely only at like 50-60Cbut i simply don't want it, space/cost/moving parts is another factori'll look for 400x100 aluminium heatsinks or somethingbut for now im not sure, not sure how much 2K/W is lies or notEDIT: found these as wellhttps://www.conrad.de/de/p/fischer-elektronik-sk-42-100-sa-strangkuehlkoerper-1-2-k-w-l-x-b-x-h-200-x-100-x-25-mm-188026.htmlbasically 200 x 100 x 25 mmso would need 8 for 400x400they are 1.2 K/W instead of theoretical 1.0K/Wlookming for alternatives, don't like the fan idea

author: OM222O
author_rank: Frequent Contributor
timestamp: August 02, 2022, 06:41:19 pm
content: Quote from: DeadlyChemist on August 02, 2022, 04:29:37 pmTrust me, manufacturers always advertise their best possible number, so it won't be any better than 2C/W, besides the design does not seem like a passive one. I mean just have a look at these passive heat sinks for CPUs:They have much thicker, longer, and spaced-out fins.Quote from: DeadlyChemist on August 02, 2022, 04:29:37 pmNope, that's a terrible idea: smaller fans have to spin much faster to move the same amount of air, so they consume more power and produce A LOT more noise. If you want to add fans, go with 140mm from either Noctua or be quiet (I think they're called silent wings). Adding temperature measurements to that many LEDs would be a challenge on its own, so you should base your fan curve on power draw. Obviously, you can test the temps to optimize the fan curve for noise while keeping things below 60C (if you're measuring the temperature of the heat sink or spreader plate, you should aim for a max of 50C).2C/W is not a lie, but I'm fairly certain they came up with that using a ton of airflow.The new heat sinks are wider, not longer (wrong direction (I don't recommend using 200mm fans)).Again, from all the testing I did, a 3mm plate, 4 heat sinks, and 4 140mm fans seemed like the best choice and simplest construction (and cheap), but the final decision is up to you.You only need the fans to come on at higher powers(I will try to find the max power level with 4 passive heat sinks) and either Noctua or be quiet fans are optimized for noise, so you should be fine.

author: OM222O
author_rank: Frequent Contributor
timestamp: August 03, 2022, 03:30:37 am
content: I ran the numbers again using the most optimal layout I could come up with from previous simulations and at full power and without fans, the max temp was 63.5C (add about 10C to all the numbers because of thermal paste):I then reduced the power in 10% (16 watts) increments which resulted in:As you can see, it's roughly 4C per increment (0.25C/W), meaning you can probably go to 60% power without running the fans (I'd go with 50% just to be safe). I finally ran the simulation again using fans which resulted in:To mount the fans, you can easily use 16 standoffs that are mounted to the 3mm plate. Are you happy with this as the final version? If yes I can finally finish the PCBs (stackable design would work without any issues here) or do you want to make some changes?

author: DeadlyChemist
author_rank: Regular Contributor
timestamp: August 03, 2022, 06:48:20 pm
content: questioning my life atm buuutyeah i guess i gotta go 3-5mm plate and 4 or preferably more heatsinks + a slow large, mostly turned off fan (i assume as big as i can fit noctua)can you make a more or less visual of how it would look like? and how much clearance do i need from the celling to the fan so it can propearly "grab" airthe only problem i have now is that it will get much more expensive because of shipping 3x instead of free shippingyes, you can design the power boards

author: OM222O
author_rank: Frequent Contributor
timestamp: August 04, 2022, 08:30:52 pm
content: Quote from: DeadlyChemist on August 03, 2022, 06:48:20 pmThis definitely got out of hand for a simple light (500x500m frame weighing around 10KGs) You may want to consider breaking this up into 4 smaller panels, each having 4 LEDs. That way you can eliminate the heat spreader plate as well saving some cost there.But as it stands, here is the final design:https://a360.co/3vGPL9pI only included 1 fan as the model is really detailed and starts lagging the computer if I added 4. The fans need about 5cm of clearance to properly cool, so the overall stack height is about 15cm.I also didn't realize how expensive fans have become (look for Noctua NF-A14 or its industrial PPC version which has better build quality). I still doubt you need that much LED power in one panel. If you break it into 4 panels, then the added height can even look good! Something similar to these:Although I'm not sure how easy it is to find 140mm or 120mm square metal tubes or if you have access to a CNC (you need to cut out slots for ventilation, could be done by hand, but it'll be messy and look weird).Alternatively, you can run the LEDs at 50% maximum brightness and avoid using fans, which should extend their life significantly.Do you want to go with the large panel idea (500x500m frame, 400x400mm LED area) or do you want to consider a redesign for 4 smaller panels?Edit:here is a simulation of 4 LEDs directly on a heat sink with a fan:even adding 10c for thermal paste, it's fairly cool at max power.

author: amaschas
author_rank: Regular Contributor
timestamp: August 06, 2022, 05:10:21 am
content: Take it from someone who has just spent the last few years trying to design an LED application that utilized PWM dimming at a high enough frequency that it won't flicker on camera/video: use analog dimming for your implementation. Also the guy who recommended a DC/DC switching constant current LED driver on the first page had the right idea. The switching frequency of a SMPS is so high that there is no chance you will be able to see a noticeable flicker. In fact, the human eye can't see flicker above a few hundred hertz. On top of that, while a SMPS switches at a certain frequency, unless its designed really poorly (lots of voltage ripple) you are going to get a constant voltage out the other size. That's the whole point of a SMPS. There's really no need for a linear power supply for this application.The recommendation for designing LED lighting is that your PWM frequency (for dimming) has to be above 20khz. Generally these applications target 30khz, since frequencies < 30khz are in the audible range, and can produce a noticeable whine. Even the slowest SMPS operate a frequencies of a few hundred kHz, so even if voltage ripple on the output were large enough to produce a noticeable change in the LED light output, you would need special equipment with a super high frame rate to detect it.

author: tooki
author_rank: Super Contributor
timestamp: August 06, 2022, 11:26:11 am
content: Quote from: amaschas on August 06, 2022, 05:10:21 amWhat’s weird is how it must depend on the camera, too: my homemade dimmer runs at something like 25kHz, and I could not produce any flicker whatsoever with my DSLR (a Nikon D7000), no matter how hard I tried, even at the maximum shutter speed of 1/8000s.Quote from: amaschas on August 06, 2022, 05:10:21 amJust to be clear, that’s a commonly held fallacy. I’ve written about this before in other threads, and somewhere I have a big post with sources, but the absolute worst-case scenario requires 35kHz to absolutely eliminate flicker and related effects (especially the “phantom array” effect).For me, I need at least 1.5kHz to not detect flicker in everyday lighting. Some people readily detect it at over 3kHz.Quote from: amaschas on August 06, 2022, 05:10:21 amLittle by little, at least. Many people still hold onto the confusion about the sufficiency of a 60Hz frame rate and design lighting with PWM in the hundreds of Hz, which is nightmarish for flicker-sensitive folks like me.FYI, the audible range for human hearing is 20Hz-20kHz best-case (children with undamaged hearing), but typically drops to 20Hz-17kHz (or less) in adults, with the upper range dropping with age. No human on earth can hear anything like e.g. 28kHz. If a switching supply produces audible noise when switching at 28kHz, it’s because there are sub-20kHz harmonics.

author: DeadlyChemist
author_rank: Regular Contributor
timestamp: August 06, 2022, 02:35:36 pm
content: Quote from: amaschas on August 06, 2022, 05:10:21 amyeah this is the plan, sooner or later im getting a high speed camera, either something rented or might buy a chronosi want to be free in whatever camera, framerate, shutter angle i choose so sadly linear is my only option for long thermI know my powersupply (which i havent picked yet) might have flicker which would be detectable by the camera, but thats a problem for laterQuote from: OM222O on August 04, 2022, 08:30:52 pmmeh, i dont want 4 panels, it would be more work + im not able to make 4 panels look goodwhy does it have to be 500x500? cant it be 400x400? like the metal?Quote from: OM222O on August 04, 2022, 08:30:52 pmhow about i add 5 heatsinks (cross) or 8 or 9 and just use larger than 100x100 fan? like 140mm or whatever in the middle?i dont fancy spending like 100€ on fans (another reason why i didn't want fans (cost), plus fans just fail or get louder and louder)

author: OM222O
author_rank: Frequent Contributor
timestamp: August 06, 2022, 05:09:47 pm
content: The frame is 500x500 because I chose 50x50x3mm angles which is one of the most common sizes (I thought you meant the window / light output area should be 400x400). If you want the frame to be 400x400, then the actual light output area would be 300x300. If you're ok with that, it's a really easy change.Like I said before, adding more heat sinks without fans doesn't do much because they get saturated by natural convection and if you want to go down the path of using fans, 4 heat sinks would be enough. If you don't care about even spacing, you can fit everything under a single 200mm fan, but all of the light would be coming from the center of the panel (edges might look dimmer) but you can shrink the panel to be about 200x200 as well.Do you want a redesign with a single 200mm fan and a smaller frame? or a 400x400 frame with everything in the middle?You can also consider water cooling with something like this:https://www.amazon.co.uk/sourcing-map-Aluminum-40x120mm-Polished/dp/B08JLNFJMN/ref=sr_1_3?crid=3ANDEO3EP9EFI&keywords=40x120+water+aluminum+water+cooling&qid=1659806267&s=electronics&sprefix=40x120+water+aluminum+water+cooling%2Celectronics%2C61&sr=1-3you still need to buy fans and a radiator so it won't be cheaper, but it can be quieter.It's VERY difficult to cool 160 watts passively; Like I said before, you can build the panel and limit the LEDs to 50% brightness, then later on if you really needed the extra output, you can always slap a few fans on top of the heat sinks. Let me know what the final decision is.

author: DeadlyChemist
author_rank: Regular Contributor
timestamp: August 07, 2022, 01:53:10 pm
content: Quote from: OM222O on August 06, 2022, 05:09:47 pmpreferably 400x400 frame, and the 400x400 plate beeing a structual part if possible?the light i guess 350x350 or 300x300, depends what can fit, but 450^2 or 500^2 and the light 400^2 works toowhat would you recommend?Quote from: OM222O on August 06, 2022, 05:09:47 pmsounds perfect, but not gonna use that due to maintance and other things needed... water is just a mess, especially 3m above me on the cellingQuote from: OM222O on August 06, 2022, 05:09:47 pmi think 1x 200mm or whatever fan and 4 heatinks with a 400^2 plate 3mm or 5mmand just spin it up once i reach some target power or temperature (pretty easy todo in software)

author: OM222O
author_rank: Frequent Contributor
timestamp: August 07, 2022, 07:37:59 pm
content: I just realized that the simulations don't match the advertised 2C/W of the heat sinks (sim shows around 0.3C/W) so the cooling design might have to wait for later, but knowing you want a 400x400mm frame and you're ok with adding a fan, I think I'll just finish up the PCBs. If you have one of those heat sinks on hand, you can do some thermal tests later to determine the number of heat sinks/fans required. Have you made an account for EasyEda? how about fusion 360?

author: MrAl
author_rank: Super Contributor
timestamp: August 08, 2022, 06:35:29 am
content: Hi,Just thought i would add a little getting here late to this thread.Yes one of the drawbacks to LEDs is that they have to have the right heatsinking and that can get rather elaborate. There have been some advancements in the lab where some of the heat is added back to the electrical current that is used to power the LED, but i dont see any of that in any LEDs yet, maybe someone else here has.The main thing though is that the main operating mode of an LED is that it requires a particular current unlike a regular incandescent bulb which requires a particular voltage. To understand this better simply swap the word "voltage" with the word "current" and the word "current" with the word "voltage" in the following description of the operation of a light bulb.A light bulb requires a certain voltage to operate correctly and with decent efficiency. If you have a 120v light bulb you apply 120 volts to it and you get proper operation, and more importantly, it 'draws' the current it needs to operate correctly when supplied with this 120 volts. By saying that it 'draws' the right current that means that we dont have to calculate or think about how much current it draws, as long as the power source can supply the voltage that we apply. In a circuit analysis that would mean we would use a light bulb and a constant voltage source.An LED is the same except it is best to drive it with a particular current. The LED then automatically goes to the correct voltage it requires to operate, as long as the current source is capable of supplying that voltage.There is a however a major difference between the two. It is not as good to 'dim' a light bulb as it is to 'dim' an LED. To dim a light bulb you reduce the voltage and the current goes down and the light bulb becomes less bright. To dim an LED you reduce the current and the voltage goes down (slightly) and the LED becomes less bright. So what's the big difference?The difference is that when we reduce the voltage to the bulb the light intensity drops more than it would if the current and voltage followed a linear curve. That means the efficacy drops by a large amount. We get less light out per electrical watt than we did at full brightness.When we reduce the current to the LED the intensity drops approximately in proportion to the current level and thus the efficacy does not drop. In fact, the efficacy actually goes up meaning we get more light output per watt.This means that if we drop the voltage to the bulb by 25 percent we get possibly only 50 percent light output, but when we drop the current to the LED by 25 percent we get around 25 percent less light output. That's a big difference, and remember the light output actually does not drop exactly in proportion the drop in light output is a little less, so when we drop the current by 25 percent the light output may only drop by 20 percent. That means we get 80 percent light output for a 75 percent current level. We also get a lot longer life. With the bulb we get a somewhat longer life but not as much as with the LED.There is one other difference worth mentioning. That is, that some LEDs are meant to be run at full current in order to ensure the color temperature does not change. That means that it is best to operate the LED at the full current if you want the right light color output. The nice thing though is that if we use a true PWM current drive, the LED always receives the max current, just less often, and so the light dims but the LED color stays the same.What this means is that the LED will be turning on and off rapidly which means it will flicker. That in turn means we have to use a high frequency, high enough that the human or pet eyes can not detect any change and it does not hurt any of us physiologically.If we wanted to be super sure that we get no flicker and no bother to any animal eyes or brain, we could simply filter the heck out of the output current. Filtering means that the LED will get a very smooth current level no matter what the current level is set for. The drawback though is that the color 'may' change although not all LEDs do change much, and the change may not be enough to bother us anyway. The advantage is higher efficacy because we are not driving (or banging) the LED at full current.Hope this helps some and good luck with the project!

author: amaschas
author_rank: Regular Contributor
timestamp: August 08, 2022, 04:38:03 pm
content: Quote from: tooki on August 06, 2022, 11:26:11 amIf your PWM signal pulses every 1/25000th of a second, the light is going to turn on and off 3 times while the shutter moves across the image. I could see you experiencing some banding at low duty cycles.Quote from: DeadlyChemist on August 06, 2022, 02:35:36 pmSo the Chronos captures ~25,000 frames in low res mode. A switching power supply turns on and offseveral hundred thousand times per second, minimum. Often they run at megahertz frequencies. And again, the only way you are even going to see a change in the light output is if the SWMP has really bad output voltage ripple problems, in which case I would recommend obtaining a better power supply. Trust me, you don't need a linear power supply for this use case.

author: DeadlyChemist
author_rank: Regular Contributor
timestamp: August 15, 2022, 04:25:01 pm
content: hey,Im still alive, just super busy with workill let you know of the easyeda account and maybe fusion360and yes, im still going linear route. im aware there are ways to make it work with high frequency but im not willing to try for this project and later possibly find out i can put my light or my camera into garbage because of banding/flicker (i had this issues too many times guys...)I dont have a heatsink on hand, i planned to buy them all at once (to save shipping)

author: tooki
author_rank: Super Contributor
timestamp: August 15, 2022, 04:50:51 pm
content: Quote from: amaschas on August 08, 2022, 04:38:03 pmIn testing, that’s exactly what I expected to see, but didn’t!!

author: DeadlyChemist
author_rank: Regular Contributor
timestamp: September 18, 2022, 04:03:07 pm
content: im not dead, moving in 2-3 weeks in a pretty nice apartment (42sqm)after i buy a table i'll continue on the project.however got this email:Part Life NotificationDear Valued Digi-Key Customer,You have purchased the following part number from Digi-Key within the last two years. The manufacturer has announced an update to the part status.Part AffectedManufacturer ONSEMI (VA)Description MOSFET N-CH 100V 5.8A DPAKManufacturer Part Number FQD7N10LTMDigi-Key Part Number FQD7N10LTMCT-NDStatus End Of LifeLast Time Buy Date 12/30/2022Substitutes Please click herebit sad ngl but oh well, i have 50 of them, should be enough i hope

author: MrAl
author_rank: Super Contributor
timestamp: September 19, 2022, 01:22:39 am
content: Quote from: DeadlyChemist on September 18, 2022, 04:03:07 pmHi,I would think there would be a thousand replacements by now made and sold. Check around maybe find another part similar.

author: John B
author_rank: Frequent Contributor
timestamp: September 19, 2022, 02:14:38 am
content: Quote from: MrAl on August 08, 2022, 06:35:29 amI experimented around with this colour temperature issue with my lighting controller project and found it to be of little to no practical concern. First step would be to purchase good quality high CRI discrete LEDs or LED panels.My understanding is that the colour spectrum would skew slightly towards the red direction of the spectrum for low currents (not red in colour necessarily, but e.g. you could have more green, which is more to the red end compared to blue.)The effect is perhaps more noticeable with 6000K LEDs vs 3000K warm white LEDs, but this is at very low currents.FWIW I settled on using low dropout linear regulation as it's very easy to have ripple free and accurate regulation from 1-700mA.