LTspice .TRAN UIC simulations with initial conditions as .IC directives

Asked Jan 14 '21 at 14:56

Active Jan 15 '21 at 10:14

Viewed 1,722 times

Starting from this question a doubt arises about the use of (global) .IC directives for 'branch currents' in LTspice (or maybe just SPICE)

Consider the .TRAN card with UIC flag. From some test done it seems to me possibly .IC directives set for inductor currents (e.g. .IC I(L1)=10) are actually not employed as initial conditions.

Is anyone aware of this? Thanks

Edit: Based on the comments received I add another screenshot for the simulation of the same circuit this time with the L1 inductor initial current set at device level (per-instance)

As you can see the result is different. This time it seems device-level condition for I(L1) is actually taken in in account. Thus for the .TRAN simulation with UIC flag it seems the global .IC directive for 'node voltages' alone is actually taken in account (to work out the voltage initial conditions for capacitors)

My question was to confirm this behavior. Thanks

edited Jan 15 '21 at 10:14

asked Jan 14 '21 at 14:56

Carlo C

Can you be more explicit in the discrepancy you're trying to point out? It's not self-evident. – Ste Kulov Jan 14 '21 at 18:06
Sure, I'm going to edit the question – Carlo C Jan 15 '21 at 09:47
If you set `ic=-10` in the inductor, you'll get the oscillations, but at twice the value. Setting it to zero creates identical outputs. Changing the sign in the `.IC` card doesn't seem to change the response. This needs more investigation. – a concerned citizen Jan 15 '21 at 17:15
Have you some other info/comment about it ? – Carlo C Jan 19 '21 at 10:46

LTspice .TRAN UIC simulations with initial conditions as .IC directives

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