×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Diodes

Diodes

(OP)
In an effort to resolve a difference of opinnion could someone difinitively validate clarify the correct purpose for a diode being placed across a relay or soleniod coil.

 Is it there to protect the coil from damage of the collapsing field;

Or is it there to protect circuit boards from the backward EMF of the collapsing field

Just a friendly disputed point of view here.

RE: Diodes

The coil could care less about the collapsing field... it handled the current going forward, it will handle it trying to continue going forward.

Dan - Owner
http://www.Hi-TecDesigns.com

RE: Diodes

I agree.  In other words, it is there to protect the drive circuit as the back EMF can be quite high.  
 

RE: Diodes

1) ...protect the coil...
2) ...protect circuit boards...

2

 

RE: Diodes

Both. A very high back EMF may damage the coil as well as other equipment.
In some applications one aspect may be more important than the other. Many coils will withstand the back EMF, some won't.
In some applications the diode may introduce a time delay on drop out.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: Diodes

This is very common for the purpose of introducing a time delay on drop out, as waross mentioned.   

RE: Diodes

It should be noted that you didn't say what the driving force of the relay was.  A diode would only be used on a DC driven coil.

Keith Cress
kcress - http://www.flaminsystems.com

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources