Voltage regulator overheating

Hi guys! I'm developing a project on Arduino Uno (Rev.2) with the original Ethernet Shield attached to it. I tried powering the boards with about 11 volts through the Vin pin, I touched the voltage regulator of the Arduino (in the Rev.2 I own the regulator is a NCP1117) and it was very very hot, so I disconnected the power supply. I tried again, but powering the boards with 7 Volts and the overheat reduces, but after a few minutes the voltage regulator becomes hot again, but fortunately less than before (I didn't measure his temperature, but for my finger was enough). Measuring the current flowing from the power supply I get about 200 mA, so I think that this is the cause of the overheating. Without the Ethernet Shield, the voltage regulator remains cold. After reading other posts on the argument, now my question is: is there anyone that tried powering up the same configuration at 7 Volts and let it running for many hours? will this thing be reliable? Could I insert a transistor in parallel with the regulator, helping the current flow towards load? I hope I'll get many answer, because it's an urgent problem :~

Your issues with the 5V regulator are fairly normal. There was a good article in Circuit Cellar that noted that overheating the voltage regulator is one of the easiest ways to hurt an Arduino. At 200ma and 7V you should only be dissipating 0.4W in the chip. It will get hot, but it might be OK.

You could try adding a small heat sink, but that is a pain. If the issue persists you could add your own 5V regulator good for an amp or so and just give the Arduino the regulated 5V on its 5V pin. You will be bypassing a fuse doing this, so take that into advisement given your application.

At that current level, yes, it will get hot. There's not a lot of heatsinking on the Arduino board.

As long as it doesn't get too hot it will be fine. I think it goes into thermal shutdown at about 125°C (check the data sheet to be sure), so anything up to that should work.

That said, you would be much better off powering the board direct into the 5V pin using a switching regulator, or a cheap 5V UBEC.

I have a mega running with external 9VDC.Like you when I connect the external power supply the regulator gets very hot with the Ethernet shield but it seems to be normal. I also get alerted by the fact it generate lots of heat but after some search I found 9V was the correct voltage to power it. Like I say I still have it running for weeks and no problem so far.

The power dissipated out of your 1117 is

P(Watt) = (Vbat - 5V)*Ibat = (11-5)*0.2A = 1.2W

The temperature of the chip junction will be (aprox):

T = th * P = 79degC/W * 1.2W = 95degC

where th is the thermal junction-to-ambient resistance of the package with 1x1inch heatsink (single side pcb copper). Without the heatsink the temperature will be aprox 163degC.

With 7V Vbat and 200mA current the temperature would be 32degC with above heatsink.

dario_show: I touched the voltage regulator of the Arduino (in the Rev.2 I own the regulator is a NCP1117) and it was very very hot, so I disconnected the power supply.

The IC can handle much more heat than your finger can.

While operating at high temperatures (>85C) can shorten the life of the silicon, regulators are designed to run hot.

The NCP1117 used on the Arduino Uno boards, for example, is designed for the silicon to not shutdown until it reaches [u]175C[/u]! [It's in the datasheet guys.] Now, this isn't to say you should run the chip that hot, until you start seeing the regulator shutdown, you are safe.

In my experiments I found that the R1 and R2 boards use a larger chip package (DPAK) than the R3 (SOT-23). The DPAK can dissipate an insane amount of power before it goes into thermal shutdown. In fact, at 500mA it wasn't until 16V was applied it started shutting down...

As for the smaller R3... Based on the amount of copper provided on the PCB and a conservative estimate of a 50C ambient, using the NCP1117's datasheet I determined the SOT-23 could dissipate 1W. From there I determined at room temperature (25C) it could dissipate 1.5W. Which means you can draw about 215mA with 12 volts in.

Running an experiment I found the package would not start shutting down until I drew over 250mA (almost 300mA). There was no thermal run-away. Measuring the package body with an IR thermometer the package kept itself around 100C. Until thermal shutdown hit, which it then ran about 10C cooler (as expected since it keeps shutting itself down.)

I tried powering the boards with about 11 volts through the Vin pin, I touched the voltage regulator of the Arduino (in the Rev.2 I own the regulator is a NCP1117) and it was very very hot, so I disconnected the power supply. I tried again, but powering the boards with 7 Volts and the overheat reduces, but after a few minutes the voltage regulator becomes hot again, but fortunately less than before (I didn't measure his temperature, but for my finger was enough).

Right... The heat is directly related to power, and power is calculated as Voltage x Current. The power dissipated in the regulator is the from the voltage dropped across the regulator. With an 11V supply, you have 6V across the regulator. With a 7V, supply you have only 2V across the regulator for about 1/3rd the power and 1/3rd the heat-rise.

Ther's sort-of a "rule-of-thumb" that if a component is too hot to touch, it's too hot. I...Not very scientific, but I'd say if you can hold your finger on the part, it's probably not too hot. If you can't hold your finger on the part, might *be too hot. *

DVDdoug:
I…Not very scientific, but I’d say if you can hold your finger on the part, it’s probably not too hot. If you can’t hold your finger on the part, might *be too hot. *
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A good rule to follow…
If it blisters your finger then you need an external 5V regulator.