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PIC on Automotive Power

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Reloadron

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A friend of mine in another forum decided to send several members Arduino Duemilanove boards to play around with. These people are more programming types than electrical electronic types. Suddenly everyone has ideas about using this board for automotive applications. I am attaching an image of the board for those who have never seen one.

These boards have a power input as seen which is followed by a regulator (onboard) and a few filter caps. The nice folks at Arduino make it a point to tell the user that the input voltage should exceed 7 volts (guessing the 5 volt reg is not low dropout) and should not exceed 12 volts. Exceeding 12 volts in will cause the little onboard regulator to get toasty.

I was thinking about using a LM2940 9.0 volt regulator. It has low dropout (don't care) but is supposed to be designed with automotive applications in mind as to things like load dumps and accidental reverse polarity (2 battery jumps).

This stuff is far from my forte so any thoughts or ideas as to if what I have in mind will work would be most appreciated.

<EDIT> This is a link to the regulator LM2940 family. I am planning TO220 case. </EDIT>

Thank You

Ron
 

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  • Arduino Board Power.png
    Arduino Board Power.png
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  • LM2940 Reg.gif
    LM2940 Reg.gif
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Why don't you just replace the on board 5V regulator with a LM2937 or LM2940? Not certain about the other components on it, but that should work.

The LM2940 as a pre-regulator will work as well. Yes, it's a good choice because of all the built in protection for automotive power spikes, reverse polarity...

EDIT: If you change the on board regulator, check the filter capacitor specs against the LM2937 or LM2940 specs.
 
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Ah, the logic behind not modifying the board is that the guys who have these things are not electrical/electronic types. That is why I figured on a pre regulator that would handle automotive power and get the voltage at a nice level in the range of the PIC card input. I have a feeling that if I suggest board modifications and replacing a surface mount part, bad things will happen. :)

I guess it is more of a them thing than a me thing. I can easily point them to a small board and the components. They should be able to do some basic soldering (slobbering) where the bigger the blob the better the job. :)

Also, I should point out that in real life the caps in my little circuit would be 47 uF and not 50 uF. The 47 uF exceeds the design spec for the caps for the regulator.

Ron
 
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The specs for this regulator, in terms of protection, seems kinda whimpy. Load dumps can be 80V and last for hundreds of mS. I think I would be more comfortable with a device especially specified for protection against such conditions, like this ( just happened to come across it while browsing, there might be other similar products )

**broken link removed**
 
Many thanks guys. The read on surge surpression was interesting and good stuff. I just don't want to see these guys wing a PIC into an automotive application and poof, it is toast. I should be able to give them some ideas and yet, keep it simple.

Thanks Again
Ron
 
For automotive applications a fuse, followed by a diode for reverse polarity with a PRV of 400 V protection and a transorb rated for 18V will do a very decent job of protecting the power input. These are large components.

You might be better off with a low component count switching regulator.

Just my thoughts.
 
Thanks KISS. I also did a simple Google search of "automotive load dump suppression" and now my head hurts. :)

This all began, as I mentioned, when a forum member gave a bunch of us this nice little gift. As conversation grew I saw all these people planning automotive applications, I haven't a clue why or what the attraction was to automotive. Most of these guys aren't just programmers but hard core programmers. They actually earn a living at programming. However, much as my programming skills are lacking (unless you want to click a button and see "Hello World") their electronic skills are lacking. Hell, I simply mentioned that plugging this card into a 12 volt automotive system was not a good idea. :)

Thus began the questions. What I was looking to do was find a somewhat simple (not 100% effective) solution for a front end for the boards. This while keeping in mind that these guys are not electronically inclined. I think the cost of the board is about $25 and the board, as the name implies Duemilanova (2009) is an old board that has been superseded in the Arduino world. Placing a complex front end for power is not exactly practical. :)

Ron
 
Hi Ron,
The circuit in the attached image should do what you want. But lets see what some other members think.......

Regards Bryan

LDO circuit.jpg
 
Thanks Brian very much. One more possible in the pile. :)

@KISS
Unfortunately the automotive environment is very hostile, but simple to tame with expensive parts.

Yeah, the key word being expensive. My goal was to keep it simple so I could give them a few pictures and a schematic and they could do it. This precludes me building a dozen of the things on a weekend for them. Which I would do but would like very much to avoid. :)

Thanks Again To All
Ron
 
This comes up every once in a while with the same answers from a regular unprotected 7805 to multiple protection levels. If this is a non-critical electronic item, nothing more than an automotive spec regulator is needed (LM2937 or LM2940 is fine) and maybe a TVS. I have old electronics that use nothing more than a reverse protection diode and a standard (non-automotive spec) regulator that have been running for years in a few vehicles with no issues and these are modified vehicles with less than stellar electrical systems. I have over a couple dozen items in cars/motorcycles now running LM2937's alone and I've never had a problem with the power supply.

If this is a critical electronics item, meaning vehicle won't run without it, then go ahead and add additional surge suppression and protection. That LT4356 from BrownOut's link looks really good and has good quantity at Digikey. With all its supporting components it will increase the size of most of my little boards by 50%, though. If I do another ECU or critical controller, I would definitely consider using it.
 
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