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I understand that the "ideal" place for a snubber diode is across the terminals of the inductive device that generates the flyback. But in the interest of making my PCB design for an Arduino shield as "bulletproof" as possible, I would like to have a suitable diode across the terminal block pins that will be connected to the device on my PCB. My question is, how do I route this?

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This is my schematic in Eagle. When when I go to the PCB layout, pin 2 of the terminal block (at the right side of the diagram above) gets connected to the ground pours. I think it would be better if it connected to an insulated trace that went first to the anode of the diode, and then joined into the ground plane. Is that correct? Or does it not really make a difference?

[My idea is that this would discourage current coming from the strike magnetics from flowing into the ground plane; it should instead flow through the diode and be dissipated by the diode's (minimal) internal resistance.]

EDIT: I have attempted a few approaches, but the only thing that has done the trick of breaking up the net from J1 pin 2 to the GND plane is putting a 0Ω resistor in the circuit (between the net with the diode and the GND). But this puts a resistor component to be lain out on the PCB, which is not exactly what I want here.

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The circuit idea is fine and so is keeping the ground/power plane away from the protection device. If you are able to define a component shape/footprint/decal in eagle then, define an SMD component with two pins that are connected by a solid lump of copper. The copper is part of the component footprint.

Thus when you route your connections, there will be one component that looks like a piece of track - make the pin connections as thin or as wide as you want to suit the track you are wanting to route.

I've used OrCAD layout and mentalgraphics PADS and this is the only sensible way I've found to deal with the problem. I haven't used EAGLE but maybe someone knows a work-around?

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  • \$\begingroup\$ I don't get what the problem is here ... I would lay the diode as near to the connector as is practical for easy manufacture then have a via to the ground plane/tracks or power tracks as needed. my only concern here is keeping the transients from interfering with other tracks/power plane.... It's been a while since I used eagle but I'm sure you can add vias.... \$\endgroup\$ – Spoon May 10 '13 at 22:55
  • \$\begingroup\$ Is the component Andy describes the same as the "virtual short" aka "star point" component? \$\endgroup\$ – davidcary May 11 '13 at 1:40
  • \$\begingroup\$ @Spoon I recognize that if you design the circuit and layout the PCB then there isn't an issue but if someone else lays out the board, it forces that person to consider taking the "right" approach. The "right" thing depends on the sensitivity of the circuits around the snubber of course. \$\endgroup\$ – Andy aka May 11 '13 at 19:48
  • \$\begingroup\$ @Andy aka, I agree, the "right" approach here would be for the Circuit designer to indicate to the PCB designer that the diode be as near as is practical to the connector if it is important. davidcary,I agree, The ground should be routed to a ground star point. All of this has to be balanced with cost/effort. For all components a professional should be document these issues on the circuit diagram if they are important. For the combined Circuit/PCB person it's not so important.... until it comes to a year later and a redesign is needed and you forgot... \$\endgroup\$ – Spoon May 13 '13 at 9:34

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