Electronic – LT-Spice RL circuit simulation ill behaved current

circuit analysisltspice

I am trying to simulate a RL circuit in DC with LT-spice as follows:
enter image description here

NOTE that the inductance is 0.0229 H although in the picture you see 229

Now, according to my calculation, what I would expect is that, because of the inductor, the current needs some time, say 4.4 tau to be close to the theoretical value of V/R = 1.497 A.

Below you can find the data of the circuit:

Inductance (H): 0.0229

Resistance (Ohm): 3.34

DC voltage (V): 5

Current (A): 1.4970059880239521

Tau: 0.006856287425149701

Critical time (s): 0.03016766467065869

Now, when I simulate the circuit in LT-spice, this is not what happens, the current jumps up to 1.497 immediately, not showing the exponential behaviour it should have in a circuit like this. What am I doing wrong I checked and doublechecked but I cannot find out what I am missing! As you can see with LT-spice I looked very close to t=0 to check whether I was missing out on the timescale, but the current behaviour is not exponential at t = 0 + dt either!

From my calculation, the theoretical behaviour before 0.03s should be the following:
enter image description here

Best Answer

You need to start the transient analysis at zero volts, else it will start at a steady state of 5VDC with the current already flowing.

Add the keyword 'startup' to the .tran string, or tick the box 'Start external DC supply voltages at 0V:' in the simulation command panel.

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