9.2.2 .IC: Set Initial Conditions
General form:
.IC V(NODNUM)=VAL V(NODNUM)=VAL ...
Examples:
.IC V(11)=5 V(4)=-5 V(2)=2.2
The IC line is for setting transient initial conditions. It has two
different interpretations, depending on whether the UIC parameter is
specified on the .TRAN control line. Also, one should not confuse this
line with the .NODESET line. The .NODESET line is only to help dc
convergence, and does not affect final bias solution (except for
multi-stable circuits). The two interpretations of this line are as
follows:
- When the UIC parameter is specified on the .TRAN line, then the node
voltages specified on the .IC control line are used to compute the
capacitor, diode, BJT, JFET, and MOSFET initial conditions. This is
equivalent to specifying the IC=... parameter on each device line, but
is much more convenient. The IC=... parameter can still be specified
and takes precedence over the .IC values. Since no dc bias (initial
transient) solution is computed before the transient analysis, one
should take care to specify all dc source voltages on the .IC control
line if they are to be used to compute device initial conditions.
- When the UIC parameter is not specified on the .TRAN control line, the
dc bias (initial transient) solution is computed before the transient
analysis. In this case, the node voltages specified on the .IC control
line is forced to the desired initial values during the bias solution.
During transient analysis, the constraint on these node voltages is
removed. This is the preferred method since it allows NGSPICE to compute
a consistent dc solution.