Contact US

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!

*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

Hbridge design

Hbridge design

Hbridge design

I am designing an H bridge using the FDMS7556S mosfet.
The datasheet states - "This device has the added benefit of an efficient monolithic Shottky body diode."
Does this mean that I can omit the catch diodes?

RE: Hbridge design

All silicon MOSFETS have a substrate source-drain diode that is a result of the semiconductor structure used. In the case of the Fairchild FDMS7556S it looks pretty good - typical forward voltage at 2A of 0.37V, 0.74V @ 35A and 44nsec typical reverse recovery.

Many times in MOSFETS this diode is not real great, and with inductive loads can result in EMI or extra heating of the MOSFET as the inductor kicks back when the MOSFET turns off. To handle the kick back in these situations, a separate diode must be added across the MOSFET with a lower forward voltage to take the current. With the FDMS7556S you will not need the extra diode unless you're driving a really high inductance, or a transformer with a high leakage inductance.

RE: Hbridge design

I'd include an external one just in case. If it turns out you need it stuff it.

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

RE: Hbridge design

Note a couple of things. Since the body diode is integral to the MOSFET, any heating issues that you might have had with the MOSFET aren't necessarily mitigated with the body diode, since they're essentially the same device. Secondly, most MOSFET body diodes have relatively poor conductance, since high conductivity is bad for MOSFET performance, so high currents might not be as efficiently removed as with a separate, dedicated diode.

FAQ731-376: Eng-Tips.com Forum Policies
[IMG http://tinyurl.com/7ofakss]
Need help writing a question or understanding a reply? forum1529: Translation Assistance for Engineers

Of course I can. I can do anything. I can do absolutely anything. I'm an expert!
There is a homework forum hosted by engineering.com: http://www.engineering.com/AskForum/aff/32.aspx

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


Low-Volume Rapid Injection Molding With 3D Printed Molds
Learn methods and guidelines for using stereolithography (SLA) 3D printed molds in the injection molding process to lower costs and lead time. Discover how this hybrid manufacturing process enables on-demand mold fabrication to quickly produce small batches of thermoplastic parts. Download Now
Design for Additive Manufacturing (DfAM)
Examine how the principles of DfAM upend many of the long-standing rules around manufacturability - allowing engineers and designers to place a part’s function at the center of their design considerations. Download Now
Taking Control of Engineering Documents
This ebook covers tips for creating and managing workflows, security best practices and protection of intellectual property, Cloud vs. on-premise software solutions, CAD file management, compliance, and more. 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