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I'm fairly new to PCB designing, but I'm loving experimenting with it. Currently, I'm trying to develop a simple PWM circuit using MOSFETs to control an RGBW strip, using an Arduino with an integrated voltage converter (design is based off this project I found). Here is a picture of my original PCB design:

PCB layout

To give an overview of the design: A barrel connector connects top right and supplies 12V and GND. This ground is then connected to the voltage converter, as well as to one of the legs of each of the MOSFETs and the GND for the Arduino to power it along with the 5V out from the converter. The Arduino will be powered from the 2 top pins on the left and then interface with the remaining pins on the left hand side, using PWM to drive the MOSFETs via a resistor. Finally, the RGBW strip attaches to the pins on the right.

Whilst I am confident with the functioning of the circuit, I had one question: Is it okay to connect all the GND pins of the MOSFETs in the way above? Or should they each have their own path like this design below?

PCB layout

As you can see, the only difference with this second design is that all the MOSFETs have a slightly different path to ground (with the exception of the white one). Will it make any difference which design I use? My main concern was that the top design would lead to voltage drop and that's why I have come to here, to find out whether it makes a significant difference or not.

P.S. I am using IRLZ44N MOSFETs and this voltage converter.

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    \$\begingroup\$ Consider rotating each of the MOSFETs 180°, which will shorten the source-to-ground leads at the expense of the gate connections (which don't matter as much). \$\endgroup\$ May 18, 2019 at 12:38
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    \$\begingroup\$ Good. Now add a polygon pour to the ground. You could also reduce the board width a bit now. \$\endgroup\$ May 18, 2019 at 13:23
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    \$\begingroup\$ After Sphero's suggestion, I wouldf consider interleaving the mosfets and the resistors, which makes the bord less wide, and increses the distance between the mosfest (more cooling, maybe room for optional heatsinks), And I would prefer to have pull-down resistors for the mosfet gates. and widen the tracks from the mosfets to the ledstrip connector. BTW is that a pin header connector? I would prefer screw connectors. \$\endgroup\$ May 18, 2019 at 16:22
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    \$\begingroup\$ pull-downs: when by accident you don't drive the mosfet gates, they could end up at a voltage that leaves the mosfet half-conducting, which can be very bad (high dissipation). Also, it protects the gates from static voltage. \$\endgroup\$ May 18, 2019 at 17:22
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    \$\begingroup\$ I only see series resistors, no pull-down resistors. \$\endgroup\$ May 18, 2019 at 17:39

3 Answers 3

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I'd turn the GND into a fill.

The difference in performance between your two designs is rather small, but you can get a lot better than both of them by making the traces wider. Filling the entire plane except for the space taken by the other traces is an extreme of that.

If you have this manufactured rather than etching it yourself, there is no reason not to go double-sided, as your design will be produced together with a lot of other double-sided designs on the same large PCB, in that case I'd turn the entire backside into a GND plane, and make two smaller zones on the front for +5V and +12V.

Having two planes gives return currents a nearby path with good coupling, so this is the best solution from an EMI perspective.

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If all mosfets are connected to the power supply through 1 wire, then the supply currents are summed and flow along this wire. Since the voltage drop is equal to the product of the current and resistance, you will decrease the voltage on each mosfet with increasing current through any mosfet. This problem is solved by supplying a separate power for each mosfets. Also, you should use the polygon of ground.

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It depends on the current through each MOSFET. But if power comes from your 3 A Power supply strips seems wide enough to avoid any voltage drop. Pretty sure the voltage drop will be much higher in your connectors. So I think 1st PCB is OK.

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