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Author Topic: Arduino Regulator: How hot is too hot?  (Read 1064 times)
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When ever I run this Arduino UNO R2 + Ethernet Shield web server for more then a few minutes, I notice that both regulators become fairly hot. I also noticed that the regulator on the Arduino itself operates significantly hotter.

The regulator on the Ethernet Shield levels out at around 106F (41C), while the regulator on the Arduino tops off at 146F (63C), which is almost untouchable.
I'm supplying a steady 9v and nothing fancy is attached to this setup, only the Ethernet Shield's Wiznet chip and its few status and data LEDs.

If anyone can provide some info on whether or not this is normal, that would be great. This little web server may be set up as a long-term thing and I'd like it to last.

In advance, Thanks
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what about checking the datasheet of the mentioned regulators and see their normal temperatures ( with and without heatsink?!?)
That way you will start getting used to reading a datasheet.
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what about checking the datasheet of the mentioned regulators and see their normal temperatures ( with and without heatsink?!?)
That way you will start getting used to reading a datasheet.

I already did, Its upper limit is 125C. I was just worried because 63C seems awfully hot for the seemingly minimal stuff it's running. (Thinking there could be a bridged set of pins somewhere.)
« Last Edit: April 23, 2012, 12:06:24 am by physics-dude » Logged

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Reference for the voltage regulator
Im gonna assume the shield u mentioned is also using a 5v rail out of Arduino right ? or the 3.3v?

U said almost untouchable, so that means wont be too bad ?!?
If u powering with it a 9V standard wall power adaptor(normally they go up to 1 A/900mA) n, shouldnt be from there.
id say 68C seems quite within reason, considering has no heatsink.




Quote
The AMS1117 series of adjustable and fixed regulators are easy to
use and are protected against short circuit and thermal overloads.
Thermal protection circuitry will shut-down the regulator should
the junction temperature exceed 165°C at the sense point.

The power dissipation of the AMS1117 is equal to:

PD = ( VIN - VOUT )( IOUT )

Maximum junction temperature will be equal to:

TJ = TA(MAX) + PD(Thermal Resistance (junction-to-ambient))

Maximum junction temperature must not exceed 125°C.

and
Thermal Resistance
Control Section -40°C to 125°C SO-8 package j JA= 160°C/W
Power Transistor -40°C to 125°C TO-252 package j JA= 80°C/W
Storage temperature - 65°C to +150°C SOT-223 package j JA= 90°C/W*
* With package soldering to copper area over backside
ground plane or internal power plane j JA can vary from
46°C/W to >90°C/W depending on mounting technique and
the size of the copper area.

Thermal Considerations
The AMS1117 series have internal power and thermal limiting
circuitry designed to protect the device under overload conditions.
However maximum junction temperature ratings of 125°C should
not be exceeded under continuous normal load conditions.
Careful consideration must be given to all sources of thermal
resistance from junction to ambient. For the surface mount
package SOT-223 additional heat sources mounted near the device
must be considered. The heat dissipation capability of the PC
board and its copper traces is used as a heat sink for the device.
The thermal resistance from the junction to the tab for the
AMS1117 is 15°C/W. Thermal resistance from tab to ambient can
be as low as 30°C/W.


Im gonna assume the shield u mentioned is also using a 5v rail out of Arduino right ? or the 3.3v?
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you already answered your question

Quote
How hot is too hot?

Quote
It's upper limit is 125C

would I want to run it at even 60 something? not really but your only over half way to deaths door (add 10 or so more degrees for actual die temps)

That being said I have never liked the thermal management on official design boards, there is just no real reason for it to get as hot as it does, I have 1+ amp loads on regulators that hover around 60 degrees and I raise a brow
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Yeah, i totally agree with you. In my opinion the footprint of it would have left space for a small heatsink, laying down on the PCB, as many other projects ive done. Makes a huge difference, specially for higher loads.
But ill guess it was a chase of cutting expenses, by making concessions.
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One thing you may want to considder is what voltage are you putting in?

If the board runs on...  say 5 volts.  And you are putting in.....  say 30 volts.  The board is needing 2 amps to work.

That is a lot of "EXTRA ENERGY" which needs to be dissipated somewhere/how.

If you supply it with 6 volts, there would be a lot less heat generated on the regulators.

Just a thought.

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2A ?!?! Got lost there...Where does those 2 A come from ?!?
USB, for example , depending on the version deliver between 500mA and 900mA.
So where you got the 2A from ?! Or have i missed something ?
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also the op mentioned feeding a steady 9 volts, the regulator on the board requires a minimum 7 volts to function, its not LDO
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If the board runs on...  say 5 volts.  And you are putting in.....  say 30 volts.  The board is needing 2 amps to work.
WTF?
Were did you get this crazy value?
Thats not true smiley-cool
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Oz
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Hey, you guys, it was an EXAMPLE!

Quote:
If the board runs on...  say 5 volts.  And you are putting in.....  say 30 volts.  The board is needing 2 amps to work.
END:


I thought I didn't need to qualify every value with the word SAY (or example)  as I did with the first one.

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Price of the product is one of the big movers, a switching buck/boost topology would be 75+% efficient...
But it takes several parts, controller, inductor, catch diode and voltage divider for output adj (optional)
and at least as many filter (better grade) caps as the linear one does, however the idea is not to provide a
general purpose power supply but to provide a stable platform from which to run a sketch. If my peripherals
draw enough current to heat op the regulator enough to notice then IMO I am doing something wrong as the
combined power and ground drop losses just might be enough to show up as noise somewhere else.
the linear regulator is basically a voltage controlled resistor, draw current through it at too large an I/O
differential and there is a GREAT DEAL of WASTED power... as heat in the regulator. At 9 v in and 100 ma load
the load Power is p = e x i so 10 ma for the regulator ( The '1117 is I think a PNP Pass type regulator, they draw
more current as the load current increases) and 100 ma for the load gives 110 ma x 9 v = .99 watts from the battery
and .5 watts for the load... So we have .49 watts wasted in the regulator as heat... 50%? Efficiency?

Doc
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as a comment to my last post there are adjustable 'buck' mode switchers available from ebay for <$2.00.
 I bought 3 of them at 1.89 ea and at 98% efficiency a 5 volt 100 ma load would dissipate 2% of .5 W (from my last post) so...
 Ploss = (100-98=02%) .02 x .5 = 10 mw as heat. The switchers are capable of a 2 amp load continuously...
according to the printed specifications, I don't know as I would draw more than 1A but they would make
great supplies for peripheral assemblies. Just to make SURE that all grounds are common.

Doc.
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