This section of the tutorial explains how to
edit parameter-extracted models. You will start with the schematic that you saved in 2.3 Edit Multi-Level Models and then continue to make changes
that more accurately reflect a practical design.
Key Concepts
This topic addresses the following key concepts:
- The correct model extraction voltage, current, and temperature parameters are required
to produce an accurate PWL MOSFET model.
- The MOSFET SPICE model is not uses in SIMPLIS simulations, instead SIMPLIS uses a PWL
model which accurately reflects the actual SPICE model behavior.
What You Will Learn
In this topic, you will learn the following:
- How to change the MOSFET SPICE model.
- How to extract a PWL model.
2.4.1 Change MOSFET SPICE
Model
In section 2.1 Add Symbols and Wires, you placed parameter-extracted models for the
MOSFET and diode without considering the suitability of the models. The IRF530 MOSFET is a
100V device with a high on-resistance; when what you need is a 30V-rated device with a lower
on-resistance. This design will use the Si4410DY MOSFET, which has a drain-source rating of
30V and an on-resistance of approximately 18mΩ.
To change Q1 to use the Si4410DY
model, follow these steps:
- Double click the MOSFET symbol.
Result: The Extract
MOSFET Parameters dialog opens.
- Click the Select button to the right of the SPICE Model field.
Result: The Select New Device dialog opens.

- In the Search field, type si441.
Result: Si4410DY
is the only model which matches the sub-string
si441 in the Installed SPICE
models list.

- Click on the Si4410DY, and then click Ok.
Result: On the Extract MOSFET Parameters dialog, the SPICE model for
Q1 changes to Si4410DY.
- Leave the dialog box open to continue after reading about the parameter extraction
routine.
2.4.2 Change the Model Extraction
Conditions
Next, you need to change the model extraction
conditions to the values used in this circuit. The parameter extraction routine requires the
following four circuit parameters:
- The Drain to source voltage in order to determine the MOSFET capacitance
values.
- The Gate drive voltage to determine the conduction characteristics.
- The Drain current to determine the threshold and transconductance
of the MOSFET.
- The Model temperature, which affects most parameters since this is the
temperature at which the SPICE simulation is performed.
For the optimum model accuracy, all four
parameters should accurately reflect the voltage, current, and temperature of the actual
circuit.
To change the model extraction conditions,
follow these steps:
- With the Extract MOSFET dialog open from the previous instructions, enter the values as
shown in the image below.
Parameter label |
Value |
Drain to source voltage |
20 |
Gate drive voltage |
5 |
Drain current |
15 |
Model temperature |
55 |
Result: The dialog should now look like the
following:

- Click Extract.
Result: The SPICE model Si4410DY is
simulated at the supplied test conditions and a PWL model is extracted for use in
SIMPLIS.
2.4.3 Save your Schematic
To save your schematic, follow these
steps:
- Select .
- Navigate to your working directory where you are saving your schematics.
- Save the file as 2_my_buck_converter.sxsch.
- When prompted to overwrite the existing file, click Ok.
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