Connect with us

Inductance of loop area

Discussion in 'Electronic Design' started by Pooh Bear, Jun 15, 2005.

Scroll to continue with content
  1. Pooh Bear

    Pooh Bear Guest

    Further to my post about the IR2110 gate driver, does anyone have a
    nice simple equation for calculating the inductance of a given loop on a
    pcb ?

    Yes I know..... we looked at it when I was about 17 / 18. Never needed
    it since then until now.

    Cheers, Graham
  2. John Larkin

    John Larkin Guest

    L = (a/100) * (7.353 * log10(16*a/d) - 6.386) uH

    a = radius, inches

    d = wire dia, inches

    courtesy Reference Data for Radio Engineers

  3. Terry Given

    Terry Given Guest

    buy a copy of Terman's Radio Engineers Handbook, then use pp47-72 for to
    solve for the geometry present. This was one of my first "old" books,
    and I have used it for this purpose for a decade or so now. Grover is
    pretty good too, but Terman suffices for most PCB-type problems.

  4. Pooh Bear

    Pooh Bear Guest

    Lol @ Radio Engineer's Handbook. That was one area I never planned to get
    involved in !

    Cheers, Graham
  5. Pooh Bear

    Pooh Bear Guest

    Hmmmm..... so for wire diameter I presumably substitute pcb track cross
    sectional area ? I hadn't imagined that to be a factor, just expected the
    'cut area' to influence.

  6. Terry Given

    Terry Given Guest

    Laugh ye not:

    rectangle of round wire, sides s1 & s2, diagonal g,
    wire diameter d
    + 0.01016*[u*delta*(s1+s2) + 2(g+d/2) - 2(s1+s2)]

    rectangle of rectangular wire, thickness b, width c (into plane of loop)
    + 0.01016*[2*g - 0.5*(s1+s2) + 0.447*(b+c)]

    all dimensions inches, L in uH. u is permeability (1.25e-6), delta is
    skin depth

  7. Pooh Bear

    Pooh Bear Guest

    Oh my God !

    Kind of thinks " why did I ask " !

    I think I prefer John's equation for simple rule of thumb !

    All this 'high frequency' stuff is quite new to me. I can make analogue and
    digital stuff work ok though !

    For small variations in d where d is fairly small to begin with does it really
    make much difference to the result ? E.g. where the cut area is a few square
    inches, does a 40 thou ( mil ) track have significantly less inductance than a
    20 thou one ?

  8. Terry Given

    Terry Given Guest

    it is little more than an LRC circuit. the trick is recognising L, R & C.
    he gives a simple loop formula:

    L = 0.00508*p*[2.303*log(4*p/d)-theta], uH

    2.303*log() = ln() so

    L = 0.00508*p*[ln(4*p/d)-theta], uH

    p = perimeter of loop, d = diameter of wire in inches
    (convert rectangle area into circular area)

    theta = shape factor
    = 2.451, circle
    = 2.561, regular octagon
    = 2.636, regular hexagon
    = 2.712, regular pentagon
    = 2.853, square
    = 3.197, equilateral triangle
    = 3.332, isoscoles right-anlge triangle

    Terman claims 0.5% accuracy. clearly theta=2.65 is a pretty good compromise.

Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day