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| Digital controlled linear current source IC simple to use? |
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| mariush:
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 on Some 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 |
| forrestc:
--- Quote from: smile on October 22, 2018, 10:22:38 am ---Do not offer specialized LED controllers as these are not linear but square wave 180KHz etc. --- End quote --- Could 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)? |
| smile:
--- Quote ---Could you explain why you can't use a PWM/square wave drive in this case? --- End quote --- I 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. --- Quote ---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. --- End quote --- Well I somehow never found any of these. --- Quote ---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)? --- End quote --- I 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 |O |
| tooki:
--- Quote from: smile on October 24, 2018, 01:25:46 pm --- --- Quote ---Could you explain why you can't use a PWM/square wave drive in this case? --- End quote --- I 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. --- End quote --- Not 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 pm --- --- Quote ---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. --- End quote --- Well I somehow never found any of these. --- End quote --- They’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 pm --- --- Quote ---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)? --- End quote --- I 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 |O --- End quote --- Well, 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. |
| smile:
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. --- Quote ---Well, 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. --- End quote --- I 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? |
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