1. Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.
    Dismiss Notice

Yet another H-Bridge

Discussion in 'Electronic Projects Design/Ideas/Reviews' started by idiot7.0, Apr 11, 2012.

  1. audioguru

    audioguru Well-Known Member Most Helpful Member

    Joined:
    Mar 16, 2004
    Messages:
    32,449
    Likes:
    937
    Location:
    Canada, of course!
    ONLINE
    Of course you are getting a short.
    The PNP and NPN transistors in series both need series base resistors.
    Right now you have the 0.7V emitter-base diode of the PNP directly in series with the 0.7V base-emitter diode of the NPN so their total is only 1.4V but you have it on the 5V supply.
     
  2. mindoverflow

    mindoverflow Member

    Joined:
    Aug 24, 2008
    Messages:
    45
    Likes:
    0
    ,,,,,
     
    Last edited: Apr 13, 2012
  3. idiot7.0

    idiot7.0 New Member

    Joined:
    Sep 9, 2011
    Messages:
    23
    Likes:
    0
    I set separate resistors for each base, it improved the design as it started functioning but the high side transistors were all the time on even with pullup resistors.

    I made some modifications and this is what I ended with. What do you think about it? It seems to be working. I do still have a doubt, will it brake the motor when both inputs are high? I don't think so.

    By going back to ronv's design, I think that setting both inputs as high would cause a full short and destroy the chips. I hope I'm not wrong once again.
     
  4. dave

    Dave New Member

    Joined:
    Jan 12, 1997
    Messages:
    -
    Likes:
    0


     
  5. ronv

    ronv Well-Known Member Most Helpful Member

    Joined:
    May 30, 2010
    Messages:
    4,725
    Likes:
    488
    Location:
    Tucson, AZ. USA

    There are acouple of ways to prevent the top and bottom transistors on at the same time. Easiest of course is not to turn them both on at the same time. ;) Or add the diodes shown:
     

Share This Page