I am designing a circuit board in dip trace to control a high power LED fixture for my aquarium. It will serve as an updated replacement for the mass of wires and smaller boards that i am currently using as a fire hazard i mean controller I want to use arduino for dimming control of constant current CAT4101 drivers for the LEDs. The fixture has 77 cree led's running at ~3.5v 1A (at max) on 4 separate 'channels'. Two have 36 LEDs, the other two have 4 and 1. The two large channels are divided into 6 strings of 6 LEDs (series) one driver chip per string with all pwm pins being joined so they all act as one. Each of the large channels have their own 24v 6.5A power supply, the smaller channels will have their own smaller power supply (yet to be purchased). The fans, micro and the driver chips themselves will be powered by a 15v 1A supply, through two LM317 making 12v and 5v. There is also going to be a mosfet/transistor combo or just a logic level fet (which ever ends up being cheaper) for pwm control of the fans.
So that's 12 grounds from the drivers on the large channels, 2 more from the smaller ones, the arduino's ground, 2 grounds for the LM317, 2 grounds for each of the 24v power supplies, the ground for the power supply for the smaller channels, the ground for the 15v supply and the ground(s) for the fan control circuit. Can I just tie all these together with one big fat trace/ground plane? is it safe to do that? is there any sort of precaution i should take to reduce damage in the event of failure? should i just purchase a single large power supply and use that to power everything? i was able to find this one for about $70 that is 24v 12A that i'd consider reasonable. Currently I'm having some odd problems with the LED's that i think might be a result of having multiple power supplies on a single mains like one channel getting dimmer right when the other one goes on.
also, is there a place where i can get a dip trace library for arduino? or even a pcb layout file or drawing (i can make components in dip trace) so that i can just put male headers on my board and plug one of my arduino dev boards into it? if i do it that way, i can just connect the 5v pin on the arduino to my 5v net and it will power the arduino without damaging anything, right? would it be better to connect to the vin pin?
sorry for all the questions! any help will be helpful and very much appreciated. Thanks!
When dealingnwith high power you are best wiring up the grounds in a star mannor as opposed to being chained one after the other.
A single large PSU is the most efficient but you have to be more careful about decoupling and supply distribution.
thanks mike for your reply. I read up a little on star grounds and i think i understand the concept. Could I use the giant copper pour that i'm going to have to do for all the CAT4101 drivers (on that chip, the heatsink is also ground) sort of as a central point for all the other grounds? Since I need 8 of those, I was thinking about doing one whole side of the board just for the drivers and a giant copper ground plane and all the other circuitry on the other side. Would this effectively be a star configuration? if yes, would it be an effective star configuration? thanks again!
Don't underestimate the voltage drop in traces, even in wide ones. Especially if you should consider daisy-chaining things and the supply voltage is close to #of-leds x Vf. This is good in terms of efficiency (the latter, not daisy-chaining), but the 'ground-bounce' (additive) may upset things, especially if you PWM things and the channels run asynchronously. This can lead to a visible beating of the brightness (= headache). To some degree this can be improved by adding large, no LARGE, capacitors, several 1000 µF, here and there.
As you already have separate drivers and separate PSUs, keep it that way. Of course this can be merged onto one PCB with multiple connectors for power and the aforementioned star topology for GND.
You should definitely avoid that 'logic ground' has to share the same path as the high currents of the led drivers. Only join them at the very last spot (star).
thank you madworm for your reply! I am not completely sure I understand everything you said but i will try my best. I try to match voltage to Vf not only because of efficiency but also because if it is much higher, the drivers get very hot and shut down. I'm reading about 'ground-bounce' right now and it is beyond my understanding of electronics (at least the wiki page is). maybe a more simplified explanation would help me understand it better. Do you think that could be causing the problem i described earlier? I do pwm the two larger channels and they go on at different times of the day. when channel one is on, it will dim down to ~50% about 1 second before channel two comes on. I should probably mention here that my current setup is not exactly what i was describing in my original post. i have three 48v power supplies that are also LED drivers in one that are used on channel two. at one point the entire setup was run by these drivers but the dimming control was not really what i wanted. Months ago I switched one of the channels over to these IC drivers, and rewired all the leds to be in strings of 6 instead of 12, with favorable results. so basically whatever I do i'm buying a new power supply. its either $40 for the 24v 6.5a supply like the one i have, or $70 for the 24v 12.5a supply, and then i have a(nother) power supply for a future project XD
You should definitely avoid that 'logic ground' has to share the same path as the high currents of the led drivers. Only join them at the very last spot (star).
this is what i was most concerned with as i know that micro's cannot handle a lot of power before death. i deally i would want to keep it completely separate. the problem is the driver chips do not have a separate logic ground. there is a vin pin, pwm/en, ground, rset (to set current) and LED, and thats it. I've seen some i think they were TI chips that had a separate gnd for pwm. anyways, if i did what i said earlier, made one entire side of the board a ground plane, doing all connections to that with vias (except the driver chips themselves which will be directly on it), would that be a sufficiently safe method of grounding everything? Thanks again!
I want to use arduino for dimming control of constant current CAT4101 drivers for the LEDs. The fixture has 77 cree led's running at ~3.5v 1A (at max) on 4 separate 'channels'. Two have 36 LEDs, the other two have 4 and 1. The two large channels are divided into 6 strings of 6 LEDs (series) one driver chip per string with all pwm pins being joined so they all act as one. Each of the large channels have their own 24v 6.5A power supply, the smaller channels will have their own smaller power supply (yet to be purchased). The fans, micro and the driver chips themselves will be powered by a 15v 1A supply, through two LM317 making 12v and 5v. There is also going to be a mosfet/transistor combo or just a logic level fet (which ever ends up being cheaper) for pwm control of the fans.