Electronics > KiCad

Power flags - Am I using them right?


Hi, being a newbie on KiCad, I am about to complete my first schematic. The ERC check sais that there are some problems about Power input pins not driven by any power output pins. So i learn that i need to use power flags. Thing is, to solve some errors, i need to put them in places where i really do not want to see a power flag! Attached some examples.

Thank you!

note: just like the voltage divider of VBUS, if i connect a power flag at the regulator input, it solves the problem but... do i really need to put it there or am I doing something wrong? |O

Note that you only need to deal with PWR_FLAG for ERC. It’s not needed otherwise.

In the first image (1.png), nodes VBUS and VEXT may be marked as power. But they are separated from the marked node by D1 and Q1 respectively. While some components have their outputs normally used as power sources, it’s not a typical function of either the cathode of a diode or the source of a MOSFET. Therefore, if U2 requires VI to be a power node, it must be marked as such. Keep in mind this is not a simulation: ERC doesn’t know the purpose and function of those components. It just checks constraints, which you feed to it.

The error in the second image (2.png) about UART_RX is valid. ERC finds an error in your diagram: you have a pin that is not driven, despite it should be.

Thank you very much!


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