Electrical models of frequently encountered loads

(published February 14 2004, Update May 13 2017)

Power ICs odften have to drive non linear, reactive or complex loads. Simulating the device with the load sometimes is far from trivial because there are no reasonable descriptions of the load in a simulation language compatible with the design flow.
The load models presented here are far from perfect but may give some starting point how th describe at lease a small signal operating point.

Stepper motor SPICE model

This is a simple spice netlist representing a small stepper motor similar to those used in automotive dynamic head light adjust. The model is very limited because in a true motor the mechanical resonances depend on the "spring constant" of the magnetic field. So in reallity it depends on the current applied. This can not be modeled because this would require a current dependent inductance in the model.

Fig. 1: Electrical model of a stepper motor

To give an example of the simulated movement of the rotor the following graph displays the ideal step (brown), the rotation of the rotor (green) and the movement of an elastically coupled load (blue).

Fig. 2: Movement of the motor. horizontal axis: time in seconds, vertical axis: rotational angle in radiants