Connection pspice diodes in series

Hi,

I am new to KiCAD.

I have a question regarding this kind of circuits:

When I run ERC it throws an error: “Input pin is not driven by any output pins” (between D2 and D3 for example).

As specified here:

Pins marked as input need to be connected to something that can drive them. Anything that is not a input or power input pin does fulfill this role.

That was for KiCad 5, though.

But if I look on ERC matrix a connection Input-pin → Input-pin seems to be allowed (green square). Sorry, I can only put one image for now…

So my questions are:

  1. Why do I get this error if ERC matrix seems to allow that?

  2. Connecting diodes in series should be a rather trivial task. Since this is a standard diode from “pspice” library I would expect this to work. Why then types of inputs for it is not “Passive” for example? Am I getting something totally wrong?

Thanks in advance.

I don’t know anything about pspice diodes, but the normal diodes (signal diodes, rectifiers) in the KiCad symbol library have pins of type passive. Reason is they could be in nets where there is no output pin but this is not an error per se. Here’s an example of a mains frequency low pass filter and squarer for driving a MCU pin (not drawn in KiCad, actually in Falstad) where the diode is to clip negative excursions.

squarer

For now I solved it for myself by replacing pspice diode using a generic LED and defining my custom SPICE model for it.

For those who will try to do it, do not forget under “Spice model” in “Properties” to change “Alternate node sequence: 2 1”.
Otherwise schematic will show that your diode is forward biased, but for SPICE due to pin numbering it is actually the opposite.

Still weird why in ERC matrix “Input pin” → “Input pin” showed green square, but ERC actually complained. Although linked tutorial from Rene_Poschl seem to imply this is the way it should be.
I think I am really getting something wrong here.

Best to use @holger’s examples (he is the maintainer of ngspice so they might be more up-to-date):

I think it’s because you fell foul of a different rule. input → input is fine, but nothing that is not input or power input to a net containing input is a problem.

you have 2 inputs connected together and that’s it.
So in this net there is no ouput driving the line.
So you get the error : “Input pin is not driven by any output pins”
That’s a normal behavior.

But the diode symbol is incorrect.