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In driving a single LED from a 9V battery, for example, you put an appropriate resistor in series with the LED, and the current is reduced. Vary the resistor, and the light intensity from the LED changes. The other way is to vary the apparent intensity is to use pulse width modulation (PWM) with the same sort of circuit, but turning the LED on and off rapidly. This all makes sense to me, and I've done this many times, for single LEDs.

I need to drive a bunch of LED panels, that are usually built up from 100+ LEDs in series/parallel. The way you can drive these is with LED drivers, like the Meanwell LPF-60D or ELG-240 series. They accept 1-10V, PWM, or variable resistor inputs to control their intensity. The good thing about these drivers is that they provide true variable current, rather than PWM chopping of the signal. I need true variable current to vary the intensity, for this particular application.

However, I've got to drive a lot (30+) panels (24 VDC, current could be up as high as 10 Amps, hence the different Meanwell drivers) at specific intensity levels via computer, and am wondering what might be a cost-effective way to do this.

These panels don't need to be varying quickly; I just need to be able to set the intensity at variable levels for various tests for a few seconds. No flashing or blinking required.

DMX controlled LED controllers are relatively ubiquitous, and they use PWM outputs (i.e., from Amazon - 32 Channel 96A RGBW DMX 512 LED Decoder Controller DMX Dimmer DC5-24V). One way is to use the DMX decoder is to drive the Meanwell units with PWM. This seems like it will work.

This may be a stretch, but I'm wondering if it is possible to modify DMX output, so the output looks like a variable current. In order to drive higher currents (limit is 3 A on the one above), I'd use a different DMX box, or multiple DMX boxes.

Is this possible, or is the DMX to Meanwell architecture the way to go? One way to drive the Meanwell units directly is with 1-10 V from some D/A board, but generating 1-10V from an analog output system seems wrong (you'd be going from digital to analog to digital).

The other advantage of the DMX system is that you don't need AC power, just DC. I didn't know if DC-DC LED controllers existed in that voltage/current range that do the same thing (without PWMing the outputs to the LEDs); the Meanwell site only shows lower current ones (only up to an amp or so).

Each individual panel will be calibrated by a solar cell/photocell so that an intensity levels can be known for each driver/LED panel pair.

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  • \$\begingroup\$ Do these panels need to be able to appear to have the same brightness to someone looking at them, if you want them to do so? Or is it okay if you cannot work out how to make them all appear to be the same? If you don't understand my question, think instead of having a display in an aircraft cockpit that has (5) 7-seg displays bought separately but installed in the same instrument. The instrument automatically dims or brightens the display based on the ambient light (time of day.) But they don't want pilots bitching that one digit looks brighter than another (flakey.) Is that your situation? \$\endgroup\$ – jonk Jan 4 '18 at 18:31
  • \$\begingroup\$ Similar; added clarification at end of post. \$\endgroup\$ – asylumax Jan 4 '18 at 18:40
  • \$\begingroup\$ Not the same question, though I am sure you think it is. I'm asking you if human perception of the brightness is important to you. I am not asking if a solar cell or photocell says so. These are, sad to say, completely different questions. (Though you did answer part of my question.) \$\endgroup\$ – jonk Jan 4 '18 at 18:51
  • \$\begingroup\$ I've worked as a consultant for Seimens' OSRAM division (before Siemens sold it) working on LED panels that had to be used as part of those outdoor video panels and had to be calibrated for human brightness and color perception. I spent quite a bit of time studying textbooks and the CIE theoretical models (there are more than one.) So the question I'm asking is coming from those years of experience calibrating devices that cannot be made precisely enough that they will look the same and must be carefully binned and/or calibrated to achieve goals engineers require when buying them. \$\endgroup\$ – jonk Jan 4 '18 at 19:00
  • \$\begingroup\$ Human perception of brightness is not important; the solar cell/photocell response is the critical element. We are using white LEDs only. \$\endgroup\$ – asylumax Jan 4 '18 at 19:09
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Is this possible,

Yes

is the DMX to Meanwell architecture the way to go?

Use multiple Mean Well HLG-240-48A or HLG-240-48B (cheapest cost per watt)
The type A has a pot to vary the current between 50% and 100%.
Type B uses 0-10v, or a resistance to set the current.

Use strings of 16 LEDs (white, blue, green) or 21 red in series (≈45v Vf). Connect as many of the strings in parallel as each HLG can support. Try to match forward voltages of the strings when connecting in parallel.

The parallel wiring will cause some current imbalance between strings. If the forward voltages are not matched well enough you will need to add current balance circuits. The easy way is to use an LM3466 with each string. Keep the temperature down with good thermal management.

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