# ltspice initial conditions and DC operating point

Another problem on Lt spice. I would like to know if I use the options uic in transient analysis but I don't specify the .IC (the initials conditions), what IC will use Lt spice for the resolution?

I did that and it ran but I was not able to see a file with DC point information.

Another question? why will a simulation fail to find the dc operating point?

• Do you have a circuit that caused DC analysis to fail? Can you share it? – The Photon Feb 15 '18 at 17:29

The use of UIC means that Spice will not go through the "initial transient solution" step (so-called "ITS") to find the DC solution at $$\t=0\$$.
However, if you are having trouble finding the DC operating point with Spice (such as with some bistable circuits), it may be because Spice assumes that all node voltages start out at $$\0\:\text{V}\$$ (relative to your ground reference, of course, where ever you placed it.) In these cases, you can use .NODESET to establish node voltages to help Spice find a specific DC solution. (Just don't use .NODESET to set the exact value you get from a previous run! Instead, just set the node voltage "near" to where you think it will arrive, later, and let Spice find the DC solution for you.)
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