Which TVS diode? Unidirectional or Bidirectional?

[blapcb]

I have a project (GPS for vehicle) where I am designing the input protection for the power supply (which is based on a L5970D). I am using a series diode against reverse polarity, and a TVS diode against transients. But, I am confused about whether I should be using a unidirectional or bidirectional TVS. I suppose, that because the other diode against reverse polarity is already there then I only need a unidirectional TVS. Is this correct?

 

[ea.arun]

unidirectional TVS will be used for dc supplies and bidirectiional is used in ac lines generally......but you can generally always use bidirectional in both cases.....in your case unidirectional....

---------- Post added at 14:54 ---------- Previous post was at 14:53 ----------

go through this app note...

https://www.onsemi.com/pub_link/Collateral/AND8424-D.PDF

 

[blapcb]

Hi Arun. Hot today in Chennai isn't it? ;-)
I am also here....

OK so I was/am planning to use SM6T series TVS from ST, design is for 12/24v vehicles. What is the breakdown voltage I should select? 34 is OK?

keep your discussion only to technical points ... this is not a chat messenger to do useless comments or chat.....

unidirectional TVS will be used for dc supplies and bidirectiional is used in ac lines generally......but you can generally always use bidirectional in both cases.....in your case unidirectional....

---------- Post added at 14:54 ---------- Previous post was at 14:53 ----------


go through this app note...

https://www.onsemi.com/pub_link/Collateral/AND8424-D.PDF

 

[ea.arun]

hi.....its always hot here....
i am really not sure about the load bump situations you will face in your power rails......or how regulated your actual supply input would be from all cranking and other issues.....
here is a good application note which will help you to determine the breakdown voltage..........

https://www.vishay.com/docs/88490/tvs.pdf