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

TVS and inductive kickback

TVS and inductive kickback

TVS and inductive kickback

Hi everyone,
I am using a TVS to protect an SSR (no zero cross circuitry) from a soleniod valve.  The specifications of the three parts in question are:

SSR:  2A continous - 100 V max
TVS: (SMBJ51CA) Bi-directional - 82 V max clamp - 7.3 A max peak pulse current
Solenoid: 1.1 A max continous - 24 VAC

My calculation for the peak pulse power is Ppeak=Imax x Vclamp = 1.1 x 82 =  90.2 W

The maximum time for the inductive kickback transient is 1ms and soleniod is only turned on every 1 minute or so.  The average power dissipated by the TVS is 90.2 x .001 /  60 = 0.0015Wavg.  This tells me that all is well since the continous power dissipation of such a part is well into the 1W area.

Am I in the clear here? Or did I miss something?


RE: TVS and inductive kickback

The TVS shall have its energy dissipation rating in Wattseconds or Joules available, to be on the safe side, since it makes a difference if:
Energy dissipation = 82 V x 7.3 A is for 1 second = 598.6 Wattseconds (or Joules), and for 1 milisecond
Energy dissipation = 82 V x 7.3 A x 0.001 second = 0.5986 Wattseconds (of Joules).
Therefore the TVS may be rated at approximately 600 Wattseconds in the first case and 0.6 Wattseconds in the second case. Obviously, the 0.6 Wattsecond rated TVS would not be able to withstand 600 Wattseconds, and it would be damaged (e.g. by the thermal runaway). The energy rating of TVS affects its physical size. The bigger energy dissipation is needed, the bigger TVS will be. Also, the peak voltage rating for the TVS is supposed to be available, in general.

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! Already a Member? Login


White Paper - PLM and ERP: Their Respective Roles in Modern Manufacturing
Leading manufacturers are aligning their people, processes, and tools from initial product ideation through to field service. They do so by providing access to product and enterprise data in the context of each person’s domain expertise. However, it can be complicated and costly to unite engineering with the factory and supply chain. Download Now
White Paper - Medical Device Design Control
Medical device product development is a highly integrated and regulated process. Implementation of a requirements tracking solution requires attention to a variety of nuanced topics. When presented with the task of tracking the many concept relationships in a project of this type, the initial software solution of choice tends to be a two-dimensional text systems. Download Now

Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close