Hi,

I am designing an automotive circuit that will use a PIC microcontroller. The automobile may be either positive or negative ground. I'm looking for some way to make sure that +5v ends up going to the microcontroller, regardless if the car is positive or negative ground.

I was looking for ideas on how to accomplish this and came across this IC.
http://www.onsemi.com/pub_link/Collateral/NIS6111-D.PDF

1. Will the NIS6111 work for my application? If so any suggestions on wiring it up;
2. If the NIS6111 won't work, any suggestions on ensuring +5v at the microcontroller for either a +ve or -ve ground vechicle. I'm trying to avoid creating two separate circuits.

Thanks for the help.
JG

 

If it were me, I'd use a simple bridge rectifier.

 

thingmaker3: I'm familar with bridge rectifier to convert AC to DC, but how would I use one to ensure constant polarity at a given point in a circuit, when inputs could be +ve or -ve?

Thanks
JG

 

It (a rectifier bridge) works the same way with DC inputs that are connected backwards, or correct polarity.

Besides, rectifier bridges are very cheap, and available everywhere. Why limit yourself to a particular design?
[eta]
Just use the + and - outputs of the bridge to supply your regulator voltage.
Have the external voltage supply connected to the AC inputs of the bridge.

[eta]
Since automotive systems are (generally) at least 6.3v (for the ancient ones), you would still have enough voltage left after a bridge rectifier for a PIC. If you want to plan for such low voltage systems, you might go to the added expense of using Shottky diodes and low-dropout regulators - but that should be an "extra cost" option.

I don't know of anyone who's made a positive earth/ground vehicle in the last 20 years or so. I don't know why anyone would do such a thing.

 

To add the SgtWookie's comment, the ones still running have been changed over to 12 volts with negative ground (the only parts that can be had require the change). Unless you have a time machine, finding a positive ground automobile is going to take some real effort.