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0-10V Dimmer to drive LED Drivers

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magnetar68

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I have 9 Meanwell ELN-60-48D LED drivers. I am using them to drive 9 strings of LEDs (3 white strings, 3 blue strings, and 3 royal blue strings -- each string as 9 CREE XP-G LEDs). These Meanwell LED drivers have a 0-10V input for controlling the dimming level.

I am using a Digital Aquatics advanced light controller (ALC) unit that outputs a 0-10V signal to dim the LEDs using separately controllable Port A and Port B.

My goal is simultaneously dim the 3 white drivers with Port A and the 6 blue/royal blue drivers with Port B.

In a perfect world I could hookup all 3 whites to Port A and all 6 blues to Port B and everything would dim.

The main problem is that the DA light controller is designed for florescent light dimmers which I read typically draw about 1mA, but I read that these LED drivers draw around 25-40mA per driver. The light controller cannot therefore feed all of these drivers. The end results is that the max voltage on the controller is less than 9V and I cannot run the LEDs at maximum intensity.

I do not know why Meanwell designed thier dimmer input to draw so much current. I am stuck with this setup as I have already bought everything and set it up.

I found a circuit **broken link removed** that will drive up to four LED drivers from a single regulated 12V power supply using an LM324 low power quad opamp.

If possible, I would like to use 1 inexpensive regulated power supply to drive ALL of the opamps (one set of 3 opamps for white and one set of 6 opamps for blues).

Assuming the worse case of a 40mA draw, then this means I need at least 360mA just for the 9 drivers (9*40=360). Plus the overhead of the opAms, I am not sure I can get away with a 12V 500mA power supply like this one. Can I?

Anyway, I have to believe this is trivial for someone with experience in this type of stuff, but my experience is limited to a few robotics projects, so I wanted to see the best way to do this. Without any guidance I would try something like this:

The regulated 500mA +12V power supply drives ALL three LM324s on their +Vcc
The portA output goes into the signal inputs of LM324-1
The portB output goes into the signal inputs on both LM324-2 and LM324-3.
LM324-1 OUT1, OUT2, and OUT3 go to the dimming inputs (+) on the three white LED drivers
LM324-2 OUTs go to the (+) on the blues
LM324-3 OUTs go to the (+) on the royal blues.
All of the IN- nodes get tied to their corresponding OUTs.
The LM324 GND nodes and all of the LED driver (-) nodes get tied to the (-) on the powersupply

Would this work? I am not sure of the total draw of the system and I don't know how much each of these LM324s would draw from the light controller.

Code:
+12V-----------------------------
          |          |          |
      LM324-1      LM324-2    LM324-3
          |          |          |
  0V------------------------------
 
40 mA seems a lot for a control input. Have you measured the input current?

The circuit that you linked to is a standard buffer circuit made with op-amps. The inputs of the op-amps will take no current (well certainly so little that it is hard to measure), so you can connect as many buffers as you want to one source.

The op-amps themselves will take hardly any current, so the 1/2 amp power supply will be fine.
 
40 mA seems a lot for a control input. Have you measured the input current?

The circuit that you linked to is a standard buffer circuit made with op-amps. The inputs of the op-amps will take no current (well certainly so little that it is hard to measure), so you can connect as many buffers as you want to one source.

The op-amps themselves will take hardly any current, so the 1/2 amp power supply will be fine.

Thanks for the response. I have not measured it myself yet, but a few folks doing these DIY LEDs for reef tanks have and they have seen somewhere around 25mA.
 
I've had a quick look at the fish forums, and to be blunt, a lot of the posters there don't understand electronics.

It seems that the ELN-60-48D needs the input to be up at 10V to work, and people have used resistors that are around 2.2 kΩ to pull the input up. Now if the input needs to be 10 V, and they are using a 12 V supply, then there can't be as much as 1mA flowing into the input under those conditions.
 
I ran a test this morning and the issue appears to be a real problem. On the three white drivers the current at 100% intensity is 5.5mA. So certainly not the 25mA per driver that others were stating. On the set of six blue drivers, the current was 8.5mA. The bigger issue, however, was the voltage across the dimmer inputs was only 6.5V, so it was only driving the LEDs at ~65%. So it looks like the 9 drivers were sinking about 14mA combined, but this is enough to overdraw from the light controller and reduce the voltage it can provide. I will need my opamp circuit.

Btw, I have also read that these drivers will burn out if more than 10.6V is applied across the dimmer inputs. If the cuircut above delivers more than 10V, where is the best place to drop the excess voltage off of the +12V regulated supply?
 
Last edited:
If I understand you correctly, your ALC cannot supply the input current to the dimmer (which as previously said, is pretty high).
Have a look at the attachment. It's an emitter follower using any high gain transistor with diode droppers to limit the maximum voltage to your device.
View attachment 62182
 
If I understand you correctly, your ALC cannot supply the input current to the dimmer (which as previously said, is pretty high).
Have a look at the attachment. It's an emitter follower using any high gain transistor with diode droppers to limit the maximum voltage to your device.
View attachment 62182

That's right, the ALC cannot provide the input current for ALL 9 of the dimmers, it seems to handle a few OK.

So this does not amplify the voltage, it just enables more current to flow at the same voltage of the input to R2? Am I asking for trouble with the LM324 solution above?

If I setup 9 of these little circuits and drove all of the from a regulated 12V power supply, I assume there would be not issues? Three of them would have the PortA+ from the ALC going into R2 and other six would have the PortB+ going into R2.

In the even the +12V is not ideal, would it help to make anything trimmable (maybe R1), so I can force the top end voltage to be exactly 10.0V?

Thanks, BTW, I do appreciate the help here.
 
This circuit does not amplify the voltage but amplifies the current available. To ensure that the circuit will not apply more than 10V then use a low dropout regulator off the 12V and remove the diodes to power the collector of the transistor. If your ALC cannot provide more than 10V and the collector voltage on the transistor is less than 10V then you cannot get more than 10V into your dimmer.
Dunno about the LM324 solution but posted this as it's simple and effective. Just try it on one of the inputs to see if it works.
R2 is just a dummy load on the emitter to regulate the measurements should you wish to measure anything without the dimmer attached.
 
OK, got it. So I only need two of these. One can drive the three white LED drivers and the other can drive the six blue drivers. This provides a pass-through of the ALC voltage and will provided the additional current required to feed the multiple LED drivers. Sounds great, I will give it a try. Thanks!
 
I had already order the LM324s so I wired this up this weekend. It works great. The ALC delivers 0-10V on both port DIMA and port DIMB with all 9 LEDs at 100% intensity. The 12V power supply delivers a total of about 40mA to the network of 3 LM324s with everything turned on at full.
 
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