.IC V(node1)=val1  [ V(node2)=val2 ]...


.IC node1 val1 [ node2 val2 ]

This statement sets transient analysis initial conditions.

node1, node2 etc. Name of circuit node (or net) to which initial condition is to be applied. See notes below.
val1, val2 etc. Voltage to be applied to net as initial condition. May be an expression containing parameters defined using .PARAM.

If the UIC parameter is specified with the .TRAN statement no DC operating point will be calculated so an initial condition will set the bias point in the same way as an IC=... parameter on a BJT, capacitor, diode, JFET or MOSFET.

If the UIC parameter is absent from the .TRAN statement then a DC operating point is calculated before the transient analysis. In this case the net voltages specified on the .IC statement are forced to the desired initial values during the DC operating point solution. Once transient analysis begins this constraint is released. By default the voltage force is effectively carried out via a 1???MATH???\Omega???MATH??? resistor. This can be changed with the option setting ICRES (see .OPTIONS).

Alternative Initial Condition Implementations

An initial condition can also be specified using a voltage source with the DCOP parameter specified. E.g.

VIC1 2 3 3.5 DCOP

Will force a voltage of 3.5 volts between nodes 2 and 3 during the DC operating point solution. This has two advantages over .IC:

  1. It has zero force resistance
  2. It can be applied differentially
You can also use a capacitor with the BRANCH parameter set to 1. E.g.:
C1 2 3 10u BRANCH=1 IC=3.5

This will behave identically to the voltage source in the above example during the DC operating point but during a subsequent small-signal or transient analysis will present a 10 F capacitance to nodes 2 and 3.

See also: Capacitor and Voltage Source.