Using a 12V automotive system to ultimately power a BS2.

Archiver

·I am intending to use a Radio Shack 7805 in the TO220 case with a heat sink attached to bring the voltage from·an automotive system down to 5V to power a BS2 stamp.
·The recent comments that indicate spikes as high as 100V could occur when the vehicle brakes are applied and fry the 7805 are very worrying.
· Is there a way of placing something between the the automotive system and the 7805, to bring the input voltage that the 7805 might see to level that is acceptable to it?
· With all the electronics on modern cars I would assume there must be a way of protecting them from potential high voltage surges.
· I would appreciate any ideas.
·

Archiver

Check out this page.

http://sproggy.mp3car.com/psu.html

Hope this helps
Bob

At 08:19 AM 6/8/00 -0400, you wrote:
> an automotive system down to 5V to power a BS2 stamp. The recent
>comments that indicate spikes as high as 100V could occur when the vehicle
>brakes are applied and fry the 7805 are very worrying. Is there a way of
>placing something between the the automotive system and the 7805, to bring
>the input voltage that the 7805 might see to level that is acceptable to
>it? With all the electronics on modern cars I would assume there must be
>a way of protecting them from potential high voltage surges. I would
>appreciate any ideas.
>

Archiver

Keith:

This subject came up here recently, and someone suggested a National LM2940
regulator, which is designed for automotive apps. It has protection for
reverse polarity and voltage spikes. There are 5 to 15 volt versions
available at 1 amp. I believe DigiKey has them. This would probably be the
"cleanest" way to go.

Good luck,
Ray McArthur

I am intending to use a Radio Shack 7805 in the TO220 case with a heat sink
attached to bring the voltage from an automotive system down to 5V to power
a BS2 stamp.
The recent comments that indicate spikes as high as 100V could occur when
the vehicle brakes are applied and fry the 7805 are very worrying.
Is there a way of placing something between the the automotive system and
the 7805, to bring the input voltage that the 7805 might see to level that
is acceptable to it?
With all the electronics on modern cars I would assume there must be a way
of protecting them from potential high voltage surges.
I would appreciate any ideas.

Archiver

You can put a series hash filter (inductor) along with a dropping resistor and then clamp it all with a zener. Not perfect but will clip most of the Smile prior to the regulator. If you use a 24 volt zener the noise, spikes, and surges that makes it thru to the zener will be clamped below the maximum input of the 7805. I have seen 7805 regulators used with no protection and work fine but I have also seen where circuits fry so if you want reliability protection is the way to go.


At 08:19 AM 6/8/00 -0400, you wrote:
>>>>


> [size=-1] I am intending to use a Radio Shack 7805 in the TO220 case with a heat sink attached to bring the voltage from an automotive system down to 5V to power a BS2 stamp.
> The recent comments that indicate spikes as high as 100V could occur when the vehicle brakes are applied and fry the 7805 are very worrying.
> Is there a way of placing something between the the automotive system and the 7805, to bring the input voltage that the 7805 might see to level that is acceptable to it?
> With all the electronics on modern cars I would assume there must be a way of protecting them from potential high voltage surges.
> I would appreciate any ideas.
> [/size]
>
>
<<<<



Larry G. Nelson Sr.
mailto:L.Nelson@ieee.org
http://www.ultranet.com/~nr