DIY LED driver for reef lighting

PWM is either on or off. There is no dimming by lowering the voltage or current. It gets full current and voltage (as set with the resistor) on and off many times per second. To our eye it looks like it dims. The amount of on time to off it was causes the brightness changes.

The 0.4 is the highest voltage allowed to guarantee the LEDS will be off. The 1.3 lis the lowest voltage to guarantee they will be on. If the voltage was one volt on the PWM I am guessing some CATs would consider that on and some off.

So Randy nope different phenomenon on the meanwells.
 
I've noticed on my CAT4101s that they are quite unstable based on their input voltage. Nothing like the datasheet shows. Basically I can get about 20%-30% increase in PAR by varying from 21V to 24V on the potrans 6.5V PSU. That's on both blues (XP-E) and whites(XP-G); 6 leds each driver. I'll try to measure the actual current one of these days, but just wanted to point it out. Has anyone seen similar results?
 
What was the voltage on a string? I am guessing 20.5, But if 21V is not enough voltage to get the current set by the sense resistor that could be part of the problem. Also IIRC I tried to adjust the power supply up until the output voltage stayed the same. It never happened. Instead the voltage started to change slower. I am not sure it would have been 20-30% but we know our eyes can't tell that change easily. So I would say that I saw the same thing.
 
DustinB said:
So you are actually getting an increase in PAR by burning off more extra voltage as heat?
Click to expand...
That would be the case if the driver was actually doing what it should, but I don't think that's the entire story. The heat does increase but also does the output of the LEDs so my guess is the current also increases.

TheFishMan65 said:
What was the voltage on a string? I am guessing 20.5, But if 21V is not enough voltage to get the current set by the sense resistor that could be part of the problem. Also IIRC I tried to adjust the power supply up until the output voltage stayed the same. It never happened. Instead the voltage started to change slower. I am not sure it would have been 20-30% but we know our eyes can't tell that change easily. So I would say that I saw the same thing.
Click to expand...

~V18.6 on the whites and ~V19.5 on the blues. I have the whites on V22.5 and the blues on V24. On all strings I can see difference in brightness by moving from the current value to within +.5 of the string. Just checking that I'm not the only one with this result :)
 
after some tests of my 1/3 build ......
so my module have 5 strings of 6leds ... here are the numbers:
all the cat4101 are set up for 700mA
Power supply:21.5V

string 1: between Cool White XRE Leds: 20.4V Current: 690mA
string 2: between Cool White XRE Leds: 19.3V Current: 690mA
string 3: between Cool White and Royal Blue XRE Leds: 19.9V Current: 660mA
string 4: between Blue Royal XRE Leds: 20V Current: 690mA
string 5: between Blue Royal XRE Leds: 20.4V Current: 680mA

What you guys think about that ?
Little concern about the string 3. Did check the resistor for the current and it's ok. Did change the string ... still have the same current. I will change the cat4101 tomorrow to see if it's a default one. Somebody had this problem before ?

Thank you
Vincent
 
terahz ... I did see that too when you increase the Voltage of the power supply ... I have the number with 21.5V ... will do the same tonight or tomorrow with 24V
 
ok did the test ... looks like the the cat4101 need more than 0.5V !! between 0.5V and 0.8V the current still going up. At 0.5V I was only at 550mA (set up for 700mA). And when I got the 0.8V, I was at 700mA

I did the test until 24V of the power supply so 3V in the CAT. Between 0.8V and 3V, nothing change ... just a lot of heat !! lol

So conclusion, we should go at 0.8V to have the 100% efficient from the CAT. Somebody saw that too ?
 
OTCHU said:
ok did the test ... looks like the the cat4101 need more than 0.5V !! between 0.5V and 0.8V the current still going up. At 0.5V I was only at 550mA (set up for 700mA). And when I got the 0.8V, I was at 700mA

I did the test until 24V of the power supply so 3V in the CAT. Between 0.8V and 3V, nothing change ... just a lot of heat !! lol

So conclusion, we should go at 0.8V to have the 100% efficient from the CAT. Somebody saw that too ?
Click to expand...

My suspicion is that this has more to do with the variation in LEDs than in the CAT4101... From what we've seen, the LEDs can vary quite significantly...

Simon
 
I agree with Simon - large LED variation. Otchu I would not worry about string 5. IIRC the circuit has a 10% variation. If anything I would worry about string 2 - with the low voltage the CAT may get kind of hot.

Sorry I did not get a change to meause mine tonight.
 
Different subject but ST just released a demoboard for showcasing one of their microcontrollers as a LED driver. It's a buck design with 4 channels on the board, each capable of 10 HP LEDs (so, 40 LEDs per board). It's $85 at Mouser. The part number is STEVAL-ILL031V1. This is about twice the cost per LED as our DIY design but might be worth playing with or reverse engineering for those looking for a "larger" capacity design.
 
Did more test today ....
I did upgrade the current on the leds at 800mA
When I was at 0.6V internal CAT, my current was at 670mA. I had to go to 1.2V to have my 800mA. Voltage on the 6leds: 21V and power supply at 22.2V ... To be honest don't understand ... the datasheet is telling us to have 0.5V minimum .... somebody have an idea ?
 
It took me multiple days, but I finally read through this whole thread and my brain hurts :lol:. Now that I know that it's both possible and affordable to DIY LED drivers, I guess I have to decide on how many LED's I actually want to drive, colors, current, optics, but I assume that's all different threads. Perhaps I should close Pandora's box before I get sucked in permanently ;)
 
Please start referencing the post number, 4994, NOT the page number. Pages are meaningless when each individual has an option to change the number of posts on an individual page.
 
Fish'InMn, but that post only gives a third of the information. I don't have time to go back and get links each time I refer to it. I can try and start remembering to add at 25 posts per page. Got a better idea?

seti, As long as EACH CAT4101 HAS ITS OWN POT you maybe ok, but keep the leads really short.
Your powering scheme should be OK. I posted somewhere and IIRC you cna have either the 5 v or 24 v come on first.
CATs probably draw a few milliamps (let's overshoot and say 25). A 500 ma supply woulld run 20. Vin and PWM can be connected to the same supply at least that is what I did.
 
One big factor to take note of when using your wall wart with the VIN, you have to keep in mind that the majority of wall warts only output their rated voltage at their rated current draw. This could mean that a 5v wall wart could push upwards of 8v or so with a tiny load on it. IIRC VIN has a max of 6v.
 
parts list

parts list

I have followed this thread as far as my headache would allow.....It sounds great...a cheap LED controller.....I am sorry if this has been asked before....can you give me an accurate up to date list of all parts needed and a step by step of assembly....and software download...to produce a good controller......sorry agian, I have gotten a headache trying to follow this thread......
 
TheFishMan65 said:
Fish'InMn, but that post only gives a third of the information. I don't have time to go back and get links each time I refer to it. I can try and start remembering to add at 25 posts per page. Got a better idea?
Click to expand...

http://www.reefcentral.com/forums/showthread.php?p=17783831#post17783831

If you don't have time to get the link every time you reference it, then just say post 4994 instead of an arbitrary page number. Are you complaining about remember a four digit number rather than a three digit number?
 
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