Designing the pcb and schematic problem


#1

Hi, I’m an electrical engineering student at University of Nottingham who need to design a pcb for my final year project. I’m designing a buck converter and I’ve counter few problems while designing it:

  1. I’m using a D-PAK (TO-252) mosfet. Everything is fined until when I’m about connect the track to the pad. This package got 2 small pad and 1 large pad which the small pad are gate and source while the big one is drain. But the software detect the large pad as gate. Any idea how can change it? Fyi Im using Q_NMOS_DGS in the schematic.
  2. I’ve already created a PCB with all footprint and track in it. But suddenly I’ve put a wrong component in the schematic. Can I still change a component in the schematic and change it to my current pcb design without messing up with my other component and track that’s been connected?

Thank you :slight_smile:


#2
  1. I guess you have three alternatives: 1. Find a Q_NMOS symbol with different D/G/S order. 2. Modify the symbol. 3. Modify the footprint.

In KiCad symbol and footprint are independent, you can attach any footprint to a symbol. The footprint only has to have at least as many pad numbers as the symbol has pins, and the application attaches a pad with a certain number to the pin with the same number. So if you modify the symbol or the footprint you have to swap some pin or pad numbers.

  1. Yes you can, it’s a basic operation, it’s difficult to imagine how one could design a complex project without doing that. But if the new footprint has a different layout or pad order than the previous one you naturally have to re-route something.

#3

Thanks for answering my question! just to clarify, after I change the component in the schematic, I need to run the CvPcb and assign the new component to a footprint and save, after that just re read the netlist in pcb design right?


#4

CvPcb is only one of the options to assign a footprint.
There are others. More details see: How can i assign a footprint to a symbol?


About kicads use of footprint and symbol: What is the difference between footprints and symbols?


#5

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