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ElectricAye
03-25-2009, 02:07 AM
Hi all,

I was looking over the spec sheet for the LM1086 voltage regulator, which I think is used on the Prop Protoboard. From what I think I understand, the LM1086 can take higher than 9 volts and still output the desired voltage of +5, or +3.3. If so, does that mean the Prop Protoboard could be operated with a +12 volt supply without any dramas? I'm asking because it might be nice to use the Vin hole on the board at +12 instead of merely +6 to +9. Am I showing my ignorance here, or is +12 a possibility?

thanks,
Mark


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[Edited to fix version of board, sorry!]

Post Edited (ElectricAye) : 3/24/2009 6:37:48 PM GMT

Chris Savage
03-25-2009, 02:23 AM
Hello,

One thing to keep in mind regarding datasheet current ratings…that’s not the only specification you need to watch. Often the power dissipation is more important. In this case we’ve listed the input voltage based on the amount of heat the regulator will have to dissipate given the input voltage and current drawn by the device. With two regulators side by side on this board with no real thermal relief, the regulator will get hotter as it dissipates more heat from a higher input voltage. That’s not to say you can’t do it, but you should be careful about how much current you’re drawing at the same time so the regulators don’t get hot and shut down. I hope this helps. Take care.

[Edit: I was assuming you were referring to the Demo Board...if you mean the PPDB it is already rated for 12V]

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Chris Savage
Parallax Engineering

mctrivia
03-25-2009, 02:25 AM
yes it can run on 12v I run it off my 18v drill battery but you need to keep current draw low or the regulator will over heat. 200ma at 12v max

if you have any put some heat sinks on the regulator.

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Need to make your prop design easier or secure? Get a PropMod (http://propmodule.com) has crystal, eeprom, and programing header in a 40 pin dip 0.7" pitch module with uSD reader, and RTC options.

ElectricAye
03-25-2009, 02:33 AM
Chris Savage (Parallax) said...
...
[Edit: I was assuming you were referring to the Demo Board...if you mean the PPDB it is already rated for 12V]


Sorry,
I'm talking about the Propeller Protoboard. I get confused about the different versions of boards.

Now I understand what you mean about the current draw/overall wattage passing through the system. My power needs are small, so I'm guessing it will be okay.

Thanks you guys, that is a big help!


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Chris Savage
03-25-2009, 02:35 AM
The protoboard and the demo board have similar issues, although I believe the regulators on the protoboard are a bit beefier. =) Still, higher input voltage means less output current available in this case. So if you're in the safe zone on current draw it should be fine.

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Chris Savage
Parallax Engineering

nohab
03-25-2009, 03:42 PM
I agree, I have run one of my protoboards at 12V and as long as it's just the processor and some LEDs, it's fine.
For measurement I used a very non-technic approach, touching the voltage regulator with my index finger. As long as it doesn't get hot it's ok.

Alex.Stanfield
01-26-2011, 05:43 PM
Hi, does any one have the Thermal resistance from case to ambient or junction to ambient for the LM1086's of the protoboard?

Also, has anyone had any experience mounting a heatsink over them?

Thanks

Mike Green
01-26-2011, 06:16 PM
"thermal resistance" - no

I had a controller using the Protoboard where the 5V regulator would run hot and I wanted to reduce the temperature. I got a finned aluminum extrusion heatsink (http://www.radioshack.com/product/index.jsp?productId=2102857) from RadioShack and glued it to the top of the regulators with some metal-filled epoxy cement ... not a huge blob, just covered the tops of the regulators with a thin layer, enough to fasten the heatsink and assure good broad contact. The particular heatsink nicely fit in the area on the board without touching anything else ... worked great.

Ding-Batty
01-26-2011, 08:03 PM
Hi, does any one have the Thermal resistance from case to ambient or junction to ambient for the LM1086's of the protoboard?

Also, has anyone had any experience mounting a heatsink over them?

Thanks

Google is your friend:
http://www.google.com/search?sclient=psy&hl=en&site=&source=hp&q=LM1086+datasheet&btnG=Google+Search

the first link:
http://www.national.com/ds/LM/LM1086.pdf

Page 10 discusses the "Thermal Considerations" including determining the Junction to Ambient thermal resistance.

Alex.Stanfield
01-27-2011, 04:52 PM
Mike: Thanks a lot. I'm understanding that you just glued the heatsink to the plastic part (top) of the regulator so did not bend it to get to the metalic part?

Ding: Sure I got google on my list, and the spec sheet too, thanks. However it doesn't state what the Rth-ja is, only Rth-jc so I was wondering what is the default (no heatsink) Rth-ca or Rth-ja in order to estimate if it would run ok with a 12V battery (13,8v when fully charged) and no other load (for the board) besides the protoboard and a couple of leds maybe.

Mike Green
01-27-2011, 05:07 PM
Yes, I glued the heatsink to the top of the regulators with only enough epoxy to attach it and make good contact across the surface. I was careful not to get epoxy onto the leads or the board. There's not very good heat conduction through the silicone encapsulation of the regulator to the heatsink, but it was good enough for my purposes.

max72
01-27-2011, 10:19 PM
12V are ok as long as the current draw is low, even without heatsink.
The word "low" is not drawing a line but creates a safe zone, it depends... for instance serial LCD, gps, and some other stuff is ok, as long as I don't use back light....
Massimo

StefanL38
01-28-2011, 04:12 AM
fi you got a very small temperature sensor you can put on the surface you can do a raw estimation of how hot the regulator gets.
If you have some space left in your project you could put one of these very small fans to make the air moving over the regulator

a more easy way could be to add one or more regulators

example:
your inputvoltage is 24V then you could "line up" 18V-->---15V-->--12V-->--9V regulators
so each regulator has to drop only a small voltage and a small power as the complete power is distributed over the regulators.

But you have to keep in mind that the input-voltage has to be around 2V higher than the output-voltage
feeding 13V into a 12V regulator will not work properly.

best regards

Stefan

Ding-Batty
01-28-2011, 08:31 PM
Ding: Sure I got google on my list, and the spec sheet too, thanks. However it doesn't state what the Rth-ja is, only Rth-jc so I was wondering what is the default (no heatsink) Rth-ca or Rth-ja in order to estimate if it would run ok with a 12V battery (13,8v when fully charged) and no other load (for the board) besides the protoboard and a couple of leds maybe.

Sorry, I thought that you didn't have that datasheet. But for the regulator mounted on the board, it is soldered to the PC Board, which acts as the heat sink. So you can use the area of that portion of copper on the protoboard that holds the 5V regulator, and use the graph from the datasheet to get Rth-ha. Then the overall Rth-ja = Rth-jc + Rth-ch + Rth-ha. For a soldered connection to the board copper, the datasheet says to use 0 for Rth-ch.

Looking at a Protoboard image, I'd estimate the copper under the regulator as only about 90mm^2 (about 9mm x 10mm), which means there is a very high Rth-ha (not much area), probably well over 200 degreesC/W, from my eyeball interpolation of the graph.

Beyond that, I don't know enough to be of any more help -- not enough thermal experience.

Duane Degn
01-28-2011, 10:42 PM
A few years ago I purchased a heatsink and it came with a special kind of epoxy that is supposed to transfer heat better than just normal epoxy. I doubt it would make much difference in this case.

Another option for attaching a heat sink is thermal tape (http://www.sparkfun.com/products/9771). I have some but haven't tried it yet.

Humanoido
01-29-2011, 08:03 AM
Serious? Have you actually looked at the regulator mounted on the Parallax Propeller Proto Board? On my boards, the regulator is already epoxy glued to the board directly and when I tried to remove one, it would not come off unless I wanted to break the board in the process. Next, the actual regulator has only a tiny heat sink stub protruding, without any way of traditionally connecting a heat sink, or otherwise. That's why I disabled these regulators and decided to use external regulation that could be more readily and completely controlled.

Alex.Stanfield
02-17-2011, 04:17 AM
Sorry, I thought that you didn't have that datasheet. But for the regulator mounted on the board, it is soldered to the PC Board, which acts as the heat sink. So you can use the area of that portion of copper on the protoboard that holds the 5V regulator, and use the graph from the datasheet to get Rth-ha. Then the overall Rth-ja = Rth-jc + Rth-ch + Rth-ha. For a soldered connection to the board copper, the datasheet says to use 0 for Rth-ch.

Looking at a Protoboard image, I'd estimate the copper under the regulator as only about 90mm^2 (about 9mm x 10mm), which means there is a very high Rth-ha (not much area), probably well over 200 degreesC/W, from my eyeball interpolation of the graph.

Beyond that, I don't know enough to be of any more help -- not enough thermal experience.

Thanks Ding, agree with you on the high Rth-ha and given that there's no spec for mounting the heatsink over the plastic side I'll give the epoxy a try and measure the temp.

Thanks to all respondents.

Regards, Alex