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I created a basic current limiter circuit for driving Red LEDs. You can access the circuit here: https://www.circuitlab.com/circuit/k74tv6/red-led-current-limiter/

When I simulate this circuit, a DC sweep of V1 from 0V to 30V in steps of 0.1V, the simulation returns massive -1.4kV spikes. Is this a bug? There is nothing in this circuit which would cause these spikes.

Runs OK but very slowly and with (obviously) low resolution if you increase the step size to 1V.

Runs OK if you replace M1 with 2N3906 PNP BJT.

Seems like the solver in CL is still struggling.

:(

I'd recommend posting a BUG REPORT:

https://www.circuitlab.com/forums/support/topic/8s9n9hav/how-to-use-the-circuitlab-support-forum/

Note that if you run the LED string with a constant current source, you don't need R3 other than perhaps to reduce power dissipation in M1.

See also:

https://www.circuitlab.com/circuit/f646vh/2-transistor-constant-current-sink-01/

https://www.circuitlab.com/circuit/w79gy2/led-multi-string-linear-constant-current-sink-01/

https://www.circuitlab.com/circuit/w2dxdv/led-multi-string-linear-constant-current-sink-03/

Thanks for the reply. I'll post a bug report.