Here's a stupid simple NPN bjt simulation that doesn't stack up. What am I missing?

[Warrick_Walter]

I’m simulating with a builtin transistor model from KiCad 7, doing a DC sweep into the base of the transistor.

The voltage at the base looks legit, it hovers around the 0.7 volt from the B/E drop that I’d expect - but the voltage at the load (collector) remains unaffected. I am expecting this to be pulled down near ground, passing a current through the load.

I’ve spent hours messing around with these stupid transistors and I’m just not getting what I expect. (I have seen the NPN do what I expect before, and I’ve been next level stuck with a PNP simulation that refused to add up, but now even the NPN simulation is on crack)

Here’s the KiCad 7 project:

psu power input simulation.zip

[BlackCoffee]

I prefer LTspice but I do use Kicad’s NGspice (and prefer running LTspice from Kicad - see my info in this recent post).

That said, here’s my NPN (BCE). Be sure to have a good schematic, spice-models and commands. And, some homework on using the Simulator in Kicad…

Others with dedicated NGspice knowledge will chime-in, perhaps…

My NPN running in Kicad (not in LTspice, but, I can make it run in LTspice, too! And, run the schematic with either Spice or pSpice symbols/models…)

[holger]

You have named your load device ‘LOAD1’. This is an inductor, with ohmic resistance 0.
Rename it to RLOAD1, and it becomes a resistor, and the voltage v(/LOAD) drops during the sweep.

[Warrick_Walter]

Oh damn it. I havent tried yet but that is almost certainty it. I think im only just realizing how “unsmart” nspice actually is, and that KiCad is a a bit of pig on a lipstick.

It seems very easy to make schematics that simulate radically differently to what you though you designed, if you missconfigure the instructions that map to spice.

[ML9104]

So ngspice should be smart enough to recognize a certain graphic as a resistor?
I don’t think there’s ANY simulator out there able to do that.
That being said, KiCAD has an irritating “non-feature”: If you change a component value or reference in a symbol, the Spice model doesn’t change with it. You’ll have to check the Spice part to be certain.