# Incorrect current direction in an NPN transistor

My circuit is below. It has an NPN transistor. In NPN transistors, the current is supposed to flow from collector to emitter (from positive to negative), but CircuitLab shows negative current. Here is a snapshot:

I am looking at the line labelled I(R1.nA). I am sure CircuitLab is correct, but I cannot understand why it is happening.

simulate this circuit – Schematic created using CircuitLab

• R2 is bizarrely low, why is it so low? Commented Oct 5, 2023 at 14:42
• @Hearth, this is in the name of science. I don't really know what I am doing, I am trying to learn. Commented Oct 5, 2023 at 14:50
• A picoohm is about fifteen orders of magnitude too small here. That's such a small resistance that even if you had a magic 1 pΩ resistor somehow, the wires you connect to either side of it will have orders of magnitude more resistance than the resistor. I have literally never encountered anything smaller than μΩ (1 μΩ = 1000000 pΩ), and even that only in extremely high-current measurement circuitry. Typical circuits doing ordinary things will never involve resistances smaller than about 1 Ω (= 1000000000000 pΩ), and a typical resistance in this position would be about 100 Ω to 10000 Ω. Commented Oct 5, 2023 at 14:58
• @Hearth Thank you for clarification! I was experimenting with different values of resistance and pico\Omega is what left. What is puzzling to me, is that with such a low resistance I would expect infinite current and it should burn transistor and I would not be able to plot anything, but somehow everything works just fine. I am guessing NPN transistor has some resistance in it to prevent it from burning. Commented Oct 5, 2023 at 15:02
• @user1700890 No, that's the base cut-off current, the maximum current you'll get out of the base when the transistor is in cutoff. What you care about is Pₜₒₜ, the maximum allowed power dissipation. Maximum base current is not usually given directly in datasheets as it's more a function of total power (which involves base and collector current) than base current alone. Commented Oct 5, 2023 at 15:23

It's hard to tell which way around they are, so what I do when possible is plot the current from a non-ambiguous point, such as the collector of Q1. In CircuitLab this is done by plotting I(Q1.nC).