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UIC option in SPICE?

I have read all I could find about the Use Initial Conditions (UIC) option in SPICE, but I still don't fully understand it. The reason I am confused is this: When I run a DC transient analysis with UIC enabled on a simple RLC tank circuit (with all passives having an IC of '0'), shouldn't these results be the same as a DC transient simulation with *no* UIC, since they should both have a initial starting condition of 0V/0A? Yet with the simulation with no UIC enabled, the circuit reaches steady state instantly; while with the UIC option enabled it takes a finite time to reach its voltage level, then over/undershoots a few time (rings) -- as it should. What am I missing here?

Thank You,

-Bill

Reply to
billcalley
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Thanks very much for the clear answer Jonathan! Very much appreciated.

Best Regards,

-Bill

Reply to
billcalley

If UIC is not specified then SPICE does not assume zero initial conditions. By default SPICE will solve for the DC operating point of the circuit before performing a transient analysis, and use that for the initial conditions.

The originating message was also posted to sci.electronics.cad but was not cross-posted, so I have cross-posted now.

Jonathan

Reply to
Jonathan Westhues

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