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zig-zag, sort of, trace on circuit board. Why?

Discussion in 'Electronic Repair' started by meirman, Mar 27, 2005.

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  1. meirman

    meirman Guest

    I have a little power supply module, made in 1983, for a burglar
    alarm, but I've seen the same thing on other printed circuit boards:

    One of the metal traces on the non-parts side of the PCB has, in place
    of the 1/10" and 1/16" wide traces used elsewhere on the board that go
    to their destinations as quickly as possible, using straight lines, a
    half inch of one trace is zig-zag, sort of.It's really not a zig-sag
    since all of the angles are right angles, and none from Z's. Here it
    is:

    ___ ___ ___
    |___| |__| like this, except smaller segments, 2 or 3mm. Not

    even in a critical spot, afaict. It's the lead from a resistor, it
    looks like, that comes from an AC 12v transformer connection, to one
    of the 4 diodes in a bridge rectifier setup.** The first inch of
    this trace is straight for an inch, with a right angle and straight
    for another half inch.

    Why don't they just use a straight line for the rest also?

    Thanks.

    **(FWIW, the bridge is followed by a filter cap and I think a voltage
    limiting transistor with a heat sink)


    Meirman
     
  2. Its a cheap fuse.
    I have seen it in a car radio, 3 tracks, one was burnt, just solder a
    jump on tracks 2... as good as change a real fuse ;-)

    Mr Nisse
     
  3. Guest

    I agree with the idea that in this case, it's a fuse.

    In high-speed logic circuits, sometimes you see "meanders" like this to
    even out the trace length for two signals that should get there at the
    same time, or should have a path with about the same capacitance or
    resistance. They are typically much smaller than your example... maybe
    1 mm or less spacing between the loops. You can see this easily on most
    recent computer motherboards... follow the bus lines from the expansion
    card slots, memory slots, or north bridge and see. I have even seen
    these on some expansion cards, like Firewire and fast Ethernet cards. I
    am told that fancy board layout packages will insert these for you
    automagically.

    Matt Roberds
     

  4. It is an inductor to filter RF and spikes from inputs in an attempt
    to prevent false alarms. I was involved i starting an alarm company in
    the late '70s when alarms were going from relays to electronics and the
    manufacturers were more than willing to explain what they were doing to
    push the newer, and more expensive equipment.
     
  5. Art

    Art Guest

    Agreed: Much easier to actually frabricate the inductor with zig-zag traces
    rather than have a descrete coil inserted in the pcb.
     
  6. meirman

    meirman Guest

    In sci.electronics.repair on Wed, 30 Mar 2005 07:10:59 -0500 "Art"
    Thanks to all of you. In this case I think it is a filter, a
    flattened coil. I'll keep my eyes open for other instances of this
    and see if I can find the other uses too.

    Meirman
     
  7. JANA

    JANA Guest

    This is done is some high frequency circuits, to employ some inductive
    reactance, and or to add some delay to a pulse or signal. I have also seen
    traces done in a sort of coil to be an inductor. If the space is available,
    it is easier to do the inductor as a trace on the board, rather than to
    insert another component. This technique can also be a space saver in the
    assembly.

    I have also seen this done to add some resistance between two points. In
    some cases to get something like a few points of an ohm, I have seen a trace
    going all the way around a circuit board. When I worked for RCA industrial,
    they were making some circuit boards where they were using extra lengths of
    trace to have some resistance inserted. They also did a number of boards
    where the small value type inductors were done with traces.

    --

    JANA
    _____


    Its a cheap fuse.
    I have seen it in a car radio, 3 tracks, one was burnt, just solder a
    jump on tracks 2... as good as change a real fuse ;-)

    Mr Nisse
     
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