Arduino Mega 2560 HOT HOT HOT

Hi,

I have arduino mega 2560 and then I upload code and connect arduino to 12V Atmega goes very hot in few seconds.
Does anyone have the same problem and maby know how to solve this problem?

If you mean the ATmega2560 chip gets hot, that's definitely bad - remove power at once.

If it keeps doing it, its cooked.

If its the voltage regulator only that's getting hot, that is because of 12V input
voltage - using USB supply or a lower voltage like 7V on the Vin or barrel-jack
will help.

Are you powering anything off-board too?

I found problem but dont konw hot to solve it.
you see I use led strip + led strip power supply + arduino + Transistors
and if I use only power supply GND with Transistors then led strip shine very low but then I connect arduino GND together with power suply GND to transistors then led strip shine good.
I dont know if anyone understand what I just say, because its hard to imagine :slight_smile:

here is pictures to understand:
here is how I connect and atmega goes HOT:
http://postimg.org/image/lnkf857nj/

If I disconnect arduino GND then led strip shine very low:
http://postimg.org/image/a02jh9fnl/

POWER SUPPLY IS 12V

You need a resistor between control pin and transistor base.
The base pin looks like a diode to Gnd.
Limit the current into the base to 10mA:
(5V - 0.7V)/.01A = 430 ohm.
390 ohm, 470 I think are standard values that should work okay.

You must use a base resistor to the NPN - you've overloaded the Arduino pin and
this may account for the whole chip going into latch-up.

When driving a NPN BJT base you always need a current limiting resistor on the base, since
the base voltage will not go much above 0.7V

What made you try that circuit in the first place? Perhaps you used a n-MOSFET
circuit with an NPN - they are not the same.

so I have to use 470 resistor between control pin and transistor like CrossRoads say?
I use C2073 transistor

Yes.

thanks for help
sad because I'll just have to wait until the Monday before the open electronics stores.
And I have one more question:
I want to use TLC5940 because I can use 16 PWM pins, but later I understand that TLC5940 gives GND, not 5V, so I cant use it with transistors, so maby is something like TLC5940 but gives 5V?
I want 16 PWM pins because I want to use FADE effect and I have 16 led strips. Arduino mega 2560 have only 12 PWM pins

The NPN, if wired correctly, also provides a low output.
Collector to LED-, Emitter to Gnd.

Just briefly checking the data sheet indicates the TLC5490 may be just what you want. Each channel has "constant current" output that looks like an NPN transistor. Study the data sheet but I think you can connect the "-" side of the LED strip to the 5490 output, and the "+" side to a source up to 18V max. and not need a transistor or anything else.

Hi, I used the TLC5940 in a project for driving RGB-LEDs.

A few weeks into the project and being a complete n00b with electronics, I found that I needed RGB-LEDs with a common cathode[1] to drive them with the TLC-Chip.

This way you can spare yourself the hassle with the transistors, but need to do another investment.

[1] must be common anode

TLC5940 & common cathode? I don't think so.

woops* you're right. As so many times confused them cathode and anode.

I meant to say I used a common anode RGB LED.

If I may turn the issue around a little...

I'm trying to drive 5 RGB LEDs in series - RGB LEDs with common cathode (this time I'm sure, because these are my old ones which didn't work with the TLC in the first place).

I have 24V constant DC source to have enough voltage for all the LEDs. I'd like to control each color-channel separately.

So, I was wondering if I can do the same setup as above, just with an PNP-Transistor (I have an 2N3906 here currently - I think I need a stronger one though) and hook the collector up to the 24V and then further that to the emitter. And I'm putting the resistors for the voltage drop for the LEDs after the emitter.

Would that be correct?

So how do you see these RGBs connecting up?

My first circuit looked like this:

But my LEDs were lit a little all the time. So I thought, this can't be quite right.

Then I read this part here on the Arduino Playground:

Two common types of transistors are:

PNP - If the base voltage is less than the emitter voltage, then current flows from the emitter to the collector.
NPN - If the base voltage is greater than the emitter voltage, then current flows from the collector to the emitter.

Then I tried a circuit like this:

But results with that configuration were even worse. Everything was lit constantly on full power.

And now I should hook up the PNP and NPN like you showed in your illustration, shouldn't I?

Just throw this out here, try replace your NPN bipolar transistor with a logic-level N-channel MOSFET? They actually have less loss and requires simpler drive circuitry than bipolars.

Crossroads, you left out a resistor on the base of the PNP transistor.

Yep, I see that.
Either way, there isn't a way to series connect RGB LEDs and come up with a meaningful control method.