Digital controlled linear current source IC simple to use? - Page 1
Forum section: electronics / beginners

author: smile
author_rank: Regular Contributor
timestamp: October 22, 2018, 10:22:38 am
content: Hello, I'm looking for digital controlled (arduino) linear current source IC easy to use like LM317 (few external components).I need at least 5W of power, more better.This is for RGBW led.Do not offer specialized LED controllers as these are not linear but square wave 180KHz etc.I would use LM338, but the resistor to control current must be power potentiometer of very low resistance and these are not cheap, besides I was told there is no way to digitally control LM338 etc.

author: spec
author_rank: Frequent Contributor
timestamp: October 22, 2018, 10:14:59 pm
content: Quote from: smile on October 22, 2018, 10:22:38 am+ smile(1) What is the total maximum and minimum constant current required for the RGBW LED?(2) What is the maximum voltage drop across the RGBW LED at the maximum current?(3) Can you identify the RGBW LED?(4) What degree of control of the constant current do you require? For example, 8 digital data lines would give 255 steps so, if the maximum current were 5A, each step would be 19.6 mA.Quote from: smile on October 22, 2018, 10:22:38 amIt is possible to use LM338s etc as constant current generators, and control the constant current digitally but, so far, I cannot see an easy way using non-specialist chips.

author: spec
author_rank: Frequent Contributor
timestamp: October 22, 2018, 10:59:04 pm
content: Quote from: smile on October 22, 2018, 10:22:38 am+2 smileWould you be happy with a circuit where the constant current could be controlled by a normal potentiometer.If so, there is a simple circuit that would do the job

author: smile
author_rank: Regular Contributor
timestamp: October 23, 2018, 06:39:19 pm
content: Quote from: spec on October 22, 2018, 10:59:04 pmNo POT will not work, I already made LM338 current circuit with 2.2Ohm resistor for 1.90Eur instead of paying 80Eur or 100Eur. Are you guys find it also crazy that in US and Europe the wireqound POTS are crazy expensive? Why? Nichrome wire is nonexistent in these parts of the world or is made from gold?

author: smile
author_rank: Regular Contributor
timestamp: October 23, 2018, 07:23:06 pm
content: I wanted to drive something like thishttps://www.aliexpress.com/item/CREE-XML-MC-E-10W-RGBW-diodes-High-Power-led-RGBW-Color-led-red-green-blue/1809369010.html?spm=2114.01010208.3.206.eNIfRV&ws_ab_test=searchweb0_0,searchweb201602_2_10065_10068_10000009_10084_10083_10080_10082_10081_10060_10062_10056_503_10055_10054_10059_9911_10099_10078_501_10079_426_10103_10073_10102_10096_10052_10053_10050_10107_10051_10106-9911,searchweb201603_9,afswitch_5&btsid=5510bf64-5f8d-4909-8d15-4864ae161cc8Perhaps there are better LEDS.My requirement are :RGBW LED with 4000K for white.5W minimum 10W MAXI prefer it sold soldered to a star boardhttps://www.cree.com/led-components/media/documents/XLampMCE.pdfThe only problem is that this LED has 85CRI, and I need like 95 or better CRI.

author: tooki
author_rank: Super Contributor
timestamp: October 23, 2018, 07:31:19 pm
content: Quote from: smile on October 23, 2018, 06:39:19 pmUmm, you didn’t understand what (s)he’s offering. Nobody is suggestingdirectlyrunning the power through a pot. They were asking if you can do without the Arduino and just use a pot for control, in which case there are simple circuits where youcontroltheconstant-current sourcewith a normal pot.

author: smile
author_rank: Regular Contributor
timestamp: October 23, 2018, 07:36:28 pm
content: QuoteI did not think my english is that bad, I'm sorry I'm not native english.I already made constant current circuit using LM338 and 2.2Ohm POT. I got answers that LM338 can't be controlled by arduino etc.

author: tooki
author_rank: Super Contributor
timestamp: October 23, 2018, 07:59:14 pm
content: I didn’t say your English is bad.Look, spec is asking if a circuit controlled by a pot (instead of Arduino) would suffice for your purposes. You just have to say “yes” or “no.”Quote from: spec on October 22, 2018, 10:59:04 pm

author: smile
author_rank: Regular Contributor
timestamp: October 23, 2018, 08:28:44 pm
content: QuoteAs thread is named "Digital controlled" i say no.

author: Buriedcode
author_rank: Super Contributor
timestamp: October 23, 2018, 10:29:49 pm
content: Perhaps I'm missing something but why not use the PWM out of an Arduino - or any microcontroller - with an opamp and pass element like a MOSFET of even a bipolar transistor? A currentsourceis slightly trickier than a current sink, but it depends on whether you do low or high side current sensing, but as the LED's you linked appear to have no common lines (so you can drive them common anode OR common cathode) I would argue that a current sink is better.That's perhaps 4 components, and can be extremely cheap. The only downside is PWM requires pretty heavy filtering if you want reasonably low ripple, and thereby making it not the best option for very fast changes in voltage. The upside is you can have whatever resolution you wish, can be implemented with almost any micro, and is easily controlled.

author: mariush
author_rank: Super Contributor
timestamp: October 24, 2018, 11:07:49 am
content: A lot of led drivers out there allow you to set a maximum current through a resistor and then adjust current by either sending a PWM signal on the Enable pin or by setting some voltage on this enable pin (for ex. 0v..1v = off , 1v...3v 0..100% , 3v+ fully onSome work at high frequencies like 300-500kHz so flicker can be super small and you can filter output more if needed.Look LED drivers section on digikey or other sites and you'll find plenty

author: forrestc
author_rank: Unknown
timestamp: October 24, 2018, 11:31:50 am
content: Quote from: smile on October 22, 2018, 10:22:38 amCould you explain why you can't use a PWM/square wave drive in this case?That said, there are quite a few LED controllers out there which are linear, just search for 'linear led driver'. Without knowing more about your application I can't really be more specific.You mention that you need 5W. But at what voltage? What current? Are you driving chains of these, or is it a single LED? Are you going to want many of these drivers or just one big one (per color)?

author: smile
author_rank: Regular Contributor
timestamp: October 24, 2018, 01:25:46 pm
content: QuoteI cant use PWM because the this is backlight for a camera, and as such the flicker will be registered even if the eye do not see any. Because the LED will be RGBW I need to vary the colors so they can be in a state were they are very low intensity, PWM would introduce flicker in such scenario.QuoteWell I somehow never found any of these.QuoteI wanted to use a single RGBW LED 5W or 10W, I posted a link to datasheet for CREE LED. It's somehow I missed that it is only 80CRI and I need like 95 or better CRI. Looked at digikey or mouser I see no RGBW LEDS with 95CRI

author: tooki
author_rank: Super Contributor
timestamp: October 24, 2018, 11:08:57 pm
content: Quote from: smile on October 24, 2018, 01:25:46 pmNot if you use a high enough PWM speed. I’ve toyed around with PWM at aroudn 60KHz and I could not persuade it to flicker in any of the cameras I tested with, even a DSLR set to 1/8000 sec.Quote from: smile on October 24, 2018, 01:25:46 pmThey’re fairly common, and many accept either a PWM or serial input to control the output level.Quote from: smile on October 24, 2018, 01:25:46 pmWell, using RGB to tweak the light is going to ruin the CRI anyway. I’d use separate RGB LEDs and choose really good white LEDs for the white — if you really need good CRI with color temp control, get high-CRI LEDs in a few color temps and dim between them.

author: smile
author_rank: Regular Contributor
timestamp: October 25, 2018, 02:29:10 pm
content: Well PWM gets slow at low brightness, that is how it dims the light. At such conditions the camera detects flicker or image distortions at pixel level, especially if I would use R,G,B as separate photos then merge them together to make color image.QuoteI would use RGBW as convenience product meaning one chip would have white and RGB. They would be used separately meaning that I would not use RGB to "correct" the white color. The light is made for photography project, and there we have color negatives that needs to be back lighted with RGB, where positives "slides" needs to be back lighted with white 3000K 4000K only.So if there is no RGBW chip with 95CRI white then this idea will not work. I need to have 2 chips one with RGB the other with 95CRI white at 3000K or 4000K, perhaps both. That complicates things, are you sure there is no RGBW chip with 95CRI white?

author: tooki
author_rank: Super Contributor
timestamp: October 25, 2018, 02:49:45 pm
content: Quote from: smile on October 25, 2018, 02:29:10 pmPlease, I know how PWM works. Are you sure you do? You say that “PWM gets slow at low brightness”, but that’s not true. You choose a PWM frequency, and theduty cyclechanges: in oneperiod, the ratio of off to on. Thespeedis the same. The human eye is much more sensitive to changes in brightness at low illumination than high, which is why we notice any flicker more at the low end of PWM than the high end. (And persistence of vision comes into play, too.) A higher PWM frequency solves this.Anyway, you didn’t understand me. I said two things:1. PWM at very high speedwillwork fine on a camera. As long as the PWMperiodis much shorter than the shutter speed (and ideally a clean multiple), it’ll work without flicker or inconsistent exposure. (For example, if you’re using a shutter speed of 1/100sec, and you use a PWM frequency of 5KHz, then each exposure will have 50 complete PWM periods. So even if the timing is slightly off, and a picture gets 49 or 51 periods instead, that 1/50th variation is negligible.2. Many constant-current LED drivers offer PWM or serial input to control the dimming. Meaning that you give it either serial (like serial commands over SPI or I2C) or PWM input (meaning that it takes the PWM signal from your dimmer) and converts that to ananalogchange in LED current. The output is not PWM.Quote from: smile on October 25, 2018, 02:29:10 pm::shrug:: I dunno. You said they don’t exist, not me.P.S. Maybe it’s just the language barrier, but you come off as kind of argumentative.

author: smile
author_rank: Regular Contributor
timestamp: October 26, 2018, 06:32:28 pm
content: Thanks everyone for your input.So is there any constant current linear not PWM LED drivers that can be controlled by say voltage 0V-3V or PWM from arduino for my task. Perhaps somebody has first hand experience and can recommend what I need?

author: mvs
author_rank: Frequent Contributor
timestamp: October 26, 2018, 08:21:56 pm
content: Quote from: smile on October 26, 2018, 06:32:28 pmTake a look at PT4115. It is CCM buck converter for LEDs with linear dimmig capability (0.5-2.5V levels at DIM input).

author: amlu
author_rank: Contributor
timestamp: December 03, 2018, 01:22:42 pm
content: I had good results driving 10watt leds using this boards,they have pwm pin, easy to control it from an arduino.https://www.aliexpress.com/item/Free-Ship-3pcs-DC-DC-step-down-5A-constant-voltage-constant-current-module-LED-drive-solar/32811163878.html?spm=2114.search0104.3.317.36321483xbfH4h&ws_ab_test=searchweb0_0,searchweb201602_2_10152_10151_10065_10344_10130_10068_10324_10547_10342_10325_10343_10340_10548_10341_10696_10192_10190_10084_10083_10618_10307_10820_10301_10821_10303_10059_100031_10103_10624_10623_10622_10621_10620,searchweb201603_36,ppcSwitch_5&algo_expid=e06dbf02-9b40-4399-b07b-3bfdf2bef8cc-46&algo_pvid=e06dbf02-9b40-4399-b07b-3bfdf2bef8cc&priceBeautifyAB=0