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Some background:

I have a PCB with a bunch of relays on it. The purpose of the circuit, is to allow signals to pass through from one connector to another (db37), or to stop it - that's where the relays come in - to break the connection.

I have a 6 layer board with the following layer stack(signal, ground, signal, signal, power, signal).

I have +12V supply, +3.3V supply and +5V supply. The +12V is for a bunch of relays, and the +3.3V and +5V are for some microcontroller + other lower voltage ICs and components.

Some of these signals from the db37 connector MAY be higher current signals (3A) but with a frequency no more than 50khz. For the most part, we are looking at 10s of mA and 10Khz signals.

I'm using my power plane for the +12V.

My question is - can I just ground all my components to the ground plane directly or through a close proximity via or should be considering a star topology ?

Are star topologies only useful for situations where there is no dedicated ground plane ?

I suspect that because I have a dedicated ground, I should be able to simply just connect everything to ground. But PCB grounding is fairly new to me.

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  • \$\begingroup\$ What kind of sub-circuits will you have on the board? Will you have precision analog, RF? Will you have switch mode power supplies? A block diagram (or a schematic) would help answer your question. Also, it sounds odd that a seemingly simple (?) relay board requires 6 layers. \$\endgroup\$ – Nick Alexeev Jan 13 '14 at 22:27
  • \$\begingroup\$ I'll try and update my question with a block diagram later tonight or tomorrow morning. The reason for 6 layers, is that I'm confined to a tight area, and I have 41 relays per board. Since each trace is set up to handle 3A, they get rather thick. I can't route all signal paths without 4 signal layers. \$\endgroup\$ – efox29 Jan 14 '14 at 0:26
  • \$\begingroup\$ No precision analog, rf or switch mode power supply on this board, but in a future version, I'd like to have some precision analog and switch mode power supply as well. But for the time being, the main focus is just the 41 relays. \$\endgroup\$ – efox29 Jan 14 '14 at 0:30
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One of the advantages of star grounding is that you define the current paths for some signals. With a ground plane the current paths are up to the electrons and the voltage potential. You may end up causing a voltage dip or surge for one component on the board at a location where a higher surge current passes near the ground pin during, for instance, a relay activation.

It may not matter for your board, you haven't provided enough information to determine that, but the answer to your general question is:

No, a ground plane does not replace a star grounding system in all cases, and the problems a star grounding system can solve are not all resolved with a ground plane. In fact a ground plane may exacerbate certain types of problems that a star grounding system can solve.

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  • \$\begingroup\$ Thank you. I'll update my question with a block diagram that may give you some more information. But its definitly good to know that a ground plane is not a universal solve all and that depending on the circuit/application, other methods of good grounding are required. \$\endgroup\$ – efox29 Jan 14 '14 at 0:28

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