Diode simulates in reverse bias even though schematic shows it connected in forward bias


#1

The diode(the one whose inside are not filled) when connected in forward bias, shows characteristics of reverse biasing.

the other diode(color filled) shows desired characteristics.

when I create new project in workspace, I am only getting the non-color filled diode in the selection.
The solid color filled diode can be selected only in few examples.

During reconfig of libraries, I got a strange message regarding rescue of component, as you can see there, the orientation of diode is reversed.

Now I am unable to get the solid color-filled diode at all.
Can anyone help me to resolve this issue?
How do I change the orientation of diode(non-color filled) by keeping its properties same.


#2

When I select this diode(the one on the right side of the above image attached), it acts as reverse biased during ngspice simulation


#3

meanwhile this diode shows correct characteristics


#4

Are you sure the pin numbers of the model agree with the pin numbers of the symbol you used? (KiCads symbols are designed for pcb design not really for simulation. Meaning they are created to connect correctly to footprints not necessarily spice models.)


#5

Hi there, I’m using a software called eSim, which is based on kicad 4 and ngspice 26, it can support simulations.
Netlist is exported from KiCad and fed to ngspice.
What you are saying is right.
The pin numbers don’t add up. The netlists generated for the ngspice has the diode terminals reversed in case of the non-color filled one and correct for the solid colored one.
I want to figure how to change properties of the former to the latter(either I change the properties or the graphical representation)


#6

KiCad version 5 has a special field in the symbols to correct the pin ordering between symbol and spice model.

For older kicad versions you would need to change the symbol it self. (pin numbers can be changed in the symbol editor. Be aware that changing the symbol this way will make it incompatible to using it for designing pcbs.) Modified symbols should not be saved to system libraries. Save them inside your personal libs.


#7

hey,
thanks for the input.
But I found a temporary solution for it. I changed the diode properties in “<project_name>-cache.lib” and it worked.
The rescue component took care of the rest and gave me the component I wanted. Did not have to change any symbols and managed to run the simulation.
Thanks again :smile: