It also shows the default value and units for each parameter.US6356059B1 - Buck converter with normally off JFET The following table lists the 12 parameters in the computer simulation model. For a p-channel JFET use the designator PJF instead of NJF and set the parameters VTO and BETA to match the p-channel parameters. The second statement is used to define the device having name U308 as an n-channel JFET with V p (VTO) set to –4V and K(BETA) equal to K = I DSS/V P 2. The initial conditions are only used for transient analysis. The “IC” sets initial conditions for the drain-to-source and gate-to-source voltages. The “OFF” instruction turns the JFET off for the first operating point. The area, which defaults to unity, multiplies or divides parameters for the model.

The 10, 11 and 12 in the first statement are the node numbers for the drain, gate, and source. As an example, you might include statements, Square brackets indicate that the quantity is optional. The SPICE statement for a JFET is of the form, Jname nd ng ns modelname ] While we discuss SPICE in an Appendix of this text, we will now quickly review the syntax for including a JFET or MOSFET in a circuit. In many analysis situations, you would set most of the model parameters to their default values and this complex model behaves almost the same as the simplified models we have discussed. The computer is capable of tracking far more details than we can by hand, so the model can be more sophisticated than that we use for a “paper” solution. The reason there are so many parameters is that the model attempts to closely imitate the nonlinear operating curves of the device.

However, the more parameters in the model, the slower the simulation runs. The more parameters the model uses, the closer the simulation results are to the actual device operation. MICRO-CAP additional 10 parameters to the MOSFET model to bring the total to 52. The lowest level model contains 25 parameters, while higher-order models add to this list. The MOSFET SPICE model contains 42 parameters in three levels. The JFET model (the SPICE 2G.6 model) contains 12 parameters. SPICE and MICRO-CAP contain sophisticated models for JFETs and MOSFETs.

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