How do I set the initial current for an inductor or transformer winding in Transient analysis? How do I limit the current?
Spice does not allow setting initial current unless you also set the initial voltages for all the circuit nodes. This is not practical and 5Spice does not support this option. But you can often set the initial current indirectly. First, remember that Spice performs a DC operating point (DC Bias) analysis using the TIME=0 value of the SignalSource waveform before doing Transient Analysis. So the circuit is ‘live” in the DC sense at TIME=0 when Transient Analysis starts. Reducing Initial Current You can add a voltage controlled switch in series with a inductor/winding and use its resistance to reduce the current through the inductor/winding. Set the switchs OFF resistance to limit the current to the desired value. Connect the switch’s control inputs to a Signal Source and set it to generate a voltage step at TIME=0. The STEP waveform’s amplitude is zero at TIME=0 and non-zero for TIME > 0. Set the switch’s threshold so it will be open (off) at TIME=0, then close (on) when TIME > 0. Use a
