Best way for me power my LEDs

I have an arduino, and I’m trying to control a large amount of LEDs. I’m using sixteen outputs of the Arduino. Each output is going to one LED panel that holds 60xLEDs in it. It should pull 400mA. The LEDs are set up so there is three of them in series with a resistor, and 20 of them in parallel with each other (20x3 series) My power supply is 14.5v (Automotive 14.5v~12.5v) I have an idea of what I should be doing…but I have my doubt about it. Just stick a transistor between each output, LED/panel?

Other info
Single LED: 5mm blue 3.4v 20mA
Resistor value for LEDs 220ohm 1/2W
Arduino rev 3
LEDs are blinking only
Power supply Automotive 12.5v~14.5v

Doubts about the supply. 12.5~14.5volt seems to be a battery charger, unreglated. Measure the voltage without load...

16 * 400mA = 6.4Amp LED current. If you use normal NPN transistors, you will need 5-10% base current = 320 to 640mA. Too much for the Arduino.

Another option is NPN darlingtons (TIP120) and ~1% base current (1k base resistors). You will "loose" ~1volt (@400mA) across the saturated transistor, so calculate your LED current limiting resistors accordingly.

Best option is a 12volt/10Amp regulated supply (ebay). And 16 logic level mosfets.

Swap the letters E and C on your transistor board. All emitters of the transistors go to ground, and the LEDs connect between +12volt and the collectors. If possible, make that long emitter track a bit wider. That track will carry 6.4Amp. Leo..

Doubts about the supply. 12.5~14.5volt seems to be a battery charger, unreglated.

Sounds to me just like the voltage in a car :slight_smile:

A normal NPN indeed needs a to high base current. A logic mosfet is indeed a easy option.

This TIP120 works as well. A base resistor of 1k to 1k8 is fine. You have a Vce of around 0,75V so a power dissipation of around 300mW. But 0,75V is very significat to the 14.5 - 3 x 3,4V = 4.3V left for the resistor so pich the resistor accordingly.

But, like I said, the source sounds like a car. The brightness difference between 12V and 14,5v will be big. For 12V you have (12V - 3 x 3,4V) / 220ohm = 8mA. (Okay, voltage drop across the led is probably a bit lower so around 10mA). And at 14,5V you have (14,5V - 3 x 3,4V) / 220ohm = 20mA so roughly double the current! And when you consider the TIP120, lets calculate the resistor for ±20mA: (14,5V - 3 x 3,4V - 0,75V) / 20mA = 178ohm => 180ohm. At 12V we now have (12V - 3 x 3,4 - 0,75V) / 180ohm = 6mA, that’s only a third!

So if you want to use it in a car you might want to consider to change it a bit. An option would be to only put 2 in series but then you wast a whole lot more power! You can also regulate the power to the leds to lets say 12V, no matter the car voltage with a DC-DC step down converter. (Or use 3 or 4 of them to keep the load on each low). Then you can pick a resistor for 12V and the light will stay the same, no matter of the motor runs or not.

Hi, Rather than a PCB diagram, it would be better if you posted a circuit diagram so we can see the components being used and how you will be powering it all.

Can you please post a copy of your circuit, in CAD or a picture of a hand drawn circuit in jpg, png?

Tom..... :)

Hi, The LEDs and resistors should be in the collector side of the transistor not the emitter, you will have little to no base current the way you have it configured.

The emitter should be to gnd/-ve.

Tom..... :)

Yep, like Tom says. Emitter to GND, Collector to the leds+resistor and the other end to V+.

Also, print all component values on the schematic, the transistor is missing ;)

And you probably didn't understand the take the transistor in consideration part when we talked about resistor value. You might want to read that again and recalculate the resistor ;)

LightChaser: I plan on using it while my car is on only so i don't run my car dead. But it be nice if i did turn it off they will be the same level of brightness

Same brightness isn't going to happen now. Like I showed, brightness difference is going to be big. Easiest fix is to include a (or a couple to spread the load) DC-DC step down converters. And step it down to 12V, no matter is the car is running or not. Helps the overall efficiency as well :D

Current draw is significant, you can add a "don't turn on when car isn't running"-function. Or at least a "you can't leave them om when the car isn't running"-function. For example by measuring the battery voltage via the ADC