[Boatanchors] OT : TVS DIODES

[Bill Cromwell]

On Mon, 2012-09-10 at 18:10 -0400, Dick KF4NS wrote:
> I know this is a bit off topic but with all the knowledgeable guys here when it comes to some of  the 
> new stuff, I hope someone can help.
> 
> I have put together a battery eliminator for use of my HT in the car, built into a gutted battery pack. I 
> have all the components selected including ferrite beads for the + - leads from the cigar lighter which 
> is fused at 2A, fed to a 7812 regulator having in and out capacitors as recommended in the applications 
> page from the spec sheet.
> 
> It has come to my attention that I could protect the input from EMI RFI and surge by adding a TVS diode 
> in the power leads. After studying the wealth of information available on the INET, I am so confused 
> about how to choose the appropriate diode. The filters that Mouser lists for selection of a diode have 
> left me totally in doubt. I am referring  to the INFINEON brand of  diodes.
> 
> Anyone with any experience and advice to share would be greatly appreciated.
> 
> 73, Dick KF4NS
> St Petersburg, FL 33714 USA
> Keep The Glow! 


Hi Dick,

I looked up the datasheet for your regulator and the dropout overhead is
2 volts. The 12 volt regulator will do *NOTHING* until the voltage at
it's input is 14 volts. Your automotive charging circuit runs right
around that mark (some of them up to 15 Volts). Inserting diodes and
other things ahead of the regulator will probably cause dropout. I can
imagine how annoying to have it chopping in and out with a fancy filter
circuit ahead of it.

Try searching for a "low dropout" regulator instead.

73,

Bill  KU8H