Hey guys, I'm finally ready to turn my project on. Long story short, I'm powering multiple LED strip using TLC4950s (see picture below).
At first i was going to use 2 power sources (one for Arduino, and another for the LED strips - common anode). But then I read somewhere that i should be able to use one supply for both as the arduino has a regulator on board. So now I'm thinking, can I use a 12V, 7.5Amp supply through the jack and then use the VIN pin to feed the LEDs? Will the 7.5Amps be pulled through the VIN pin safely without burning up the Arduino? Should I just go back tp 2 power supplies :)...
You can use the same power supply for both purposes but do NOT try to draw 7.5A through the Vin pin. You will burn up the blocking diode on the Arduino board (and possibly some PCB traces too). Just run the 12V output from the supply to the Arduino, then run another wire from the power supply to your LED's.
Also note that breadboards are really not rated for those kinds of currents. You may well melt parts of your breadboard.
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The Rugged Motor Driver: two H-bridges, more power than an L298, fully protected
When you say run another wire from the supply to the LEDs, do you mean just a positive or also ground? I'm assuming just the positive as the ground is coming from the arduino.
The 24-mil Vin traces will heat up by about 300C at 7.5A according to my estimates. The (-) traces run on a ground plane and can carry much more current.
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The Gadget Shield: accelerometer, RGB LED, IR transmit/receive, speaker, microphone, light sensor, potentiometer, pushbuttons
I would still not run 7.5 amps through the arduino ground pin(s) to the high current load. Better to have separate properly sized +12 and ground wires to the high current load and then just a separate +12v and ground to the arduino external power connector.
The ground to the TLCs is the return from the LEDs!! Its the high current.... One neat trick is to draw your circuit, then go over in a thicker pen for all the high current paths - this will help you work out where wires need to be thicker!
Also if you think 7.5A doesn't sound that much remember that heating is proportional to current squared so 7.5A is 60 times 'worse' than 1A...
Thanks MartT. Now you have me rethinking everything. By having the high current ground connected to the TLCs, can they handle the high current? I can't see anything that speaks to amps on the spec sheet. I also assume that by having a 7.5amps avaialble doesn't mean I'm actually drawing that unless all the lights are on and dialed to white (they're RGB strips).
So if I understand this correctly, i would have external (+) to the strips (common anode), external (-) to the TLCs, and arduino (+) to the TLCs, right?
Since the high voltage has the potential of melting the breadboard, what options do i have?
loscat:
Thanks MartT. Now you have me rethinking everything. By having the high current ground connected to the TLCs, can they handle the high current? I can't see anything that speaks to amps on the spec sheet. I also assume that by having a 7.5amps avaialble doesn't mean I'm actually drawing that unless all the lights are on and dialed to white (they're RGB strips).
Since the TLC4950 is an LED driver, I would imagine that it's capable of sourcing/sinking the required currents. Nevertheless, you should closely examine the datasheet - current draw should be clearly labeled.
loscat:
So if I understand this correctly, i would have external (+) to the strips (common anode), external (-) to the TLCs, and arduino (+) to the TLCs, right?
You also want a ground wire to the Arduino =).
loscat:
Since the high voltage has the potential of melting the breadboard, what options do i have?
You can point-to-point solder with 16-18 AWG wire, make a custom PCB (this is probably your final route), or use many parallel connections (decreases resistance, and thus I2R heat losses). It's not high voltage that's the problem, by the way, just high current - breadboards have a decently high resistance, due to bad contact with the wires, and I2R's worth of power will be lost to joule heating.
Are you saying ground from the high current supply to the arduino? or ground from arduino to the board? (I'm doing that for other components such as buttons, etc...)
Also, been reading some older posts around using transistors, MOSFETs, etc... with high current. Do I need to consider any of those or will my current setup work as long as i don't melt the breadboard
also, just to make sure I'm covering all my bases, here's a few more questions:
if external power supply is putting our 12VDC, 7.5amps and I connect (+) to a strip/or power bar, can I connect each of my LED strips to the power strip using 22-gauge wire? each strip is only pulling a max of .24 amps on full white which is well under the 22-gauge rating so I'm assuming that's OK. Is the 16-18 gauge wire recommendation just from the power supply to the power strip? and is that also true for (-)? meaning lower gauge to strip and then higher gauge to the TLCs?
Thanks for your help, it will keep my office from burning down XD
if external power supply is putting our 12VDC, 7.5amps...
The external power supply provides a fixed 12 volts. If you do not connect anything to the supply then it will be 'putting out' zero amperes. Whatever you connect to the power supply draws a specific amount of current from the supply. If you connect one LED with the proper series resistor then the supply will be 'putting out' 20 mA. If you connect two such LEDs (in parallel) then the supply will be 'putting out' 40 mA. This particular supply can power any number of devices until their total current demand reaches 7.5 amps. The current rating of a power supply is like a speed limit. You can safely draw any amount of current up to this limit. You can also get away with drawing more current, but you are likely to get in trouble if you do.
Whatever current goes out of the + terminal of the power supply must ultimately go back into the - terminal. Therefore the size of the wire has to be appropriate for both + and - power supply leads.
Thanks Floresta, i guess my specific question is - does the gauge of the (-) wires going to the TLCs need to be 7.5 rated or just the wire between the power supply and the sourcing compoment (e.g. PCB, PerfBoard, etc...)?
Same question for (+), does the wire to each LED strip need to be 7.5 rated or just to whatever max current that particular strip will pull?
Finally, can I power the arduino with the same power supply feeding (+) and (-) leads to the Power Pins (Grnd and VIN)?
Examine the circuit and see what current is flowing through each wire, it is only that amount of current that needs accommodating.
However don't get too hung up on the wire rating nothing dramatic happens, it just gets a bit warm.
