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UIC option in SPICE?

B

billcalley

Jan 1, 1970
0
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
 
J

Jonathan Westhues

Jan 1, 1970
0
billcalley said:
'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

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
 
B

billcalley

Jan 1, 1970
0
Thanks very much for the clear answer Jonathan! Very much appreciated.

Best Regards,

-Bill
 
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