SIMPLIS Tutorial

2.2  Edit Component Values

Starting with the schematic that you saved in the previous section, the next step is to change the component values to more accurately reflect a practical design.

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2.2.1  Change Component Values

To change the output load resistor, follow these steps:

1. Double click the R1 symbol, making sure that you have the cross hair on the symbol - not on the label.
   Result: The Choose Component Value dialog box appears.
2. Change the Result to 120m as shown below.
   
3. Click OK.
4. Repeat steps 1 through 3, changing the values as listed below:
   

   Reference Designator	Component Name	New Value
   L1	Output Inductor	680nH
   R2	Gate Resistor	1.5Ω
   V1	Input Source	12V

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2.2.2  Change Capacitance Value

To change the output capacitor value, follow these steps:

1. Double click the C1 symbol.
   Result: The Edit Device Parameters dialog appears.
2. Change the Capacitance value to 220uF as shown below.
   

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2.2.3  Change Curve Labels on Probes

To rename the probes, follow these steps:

1. Double click the Probe1-NODE symbol.
   Result: The Edit Probe dialog opens.
   
2. In the Curve label text box, change the name to VOUT
   .
3. Click OK.
4. Repeat steps 1 through 3, changing the curve labels for the other probes as indicated below:
   

   Old Curve Label	Circuit Variable	New Label
   Probe2 NODE	Switching Node	SW
   IPROBE1	Inductor Current Probe	IL

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2.2.4  Change MOSFET and Diode Models

The MOSFET and Diode require ratings that are appropriate to the specifications of the design. The IRF530 MOSFET is a 100V device; therefore, you need a 30V-rated device with an appropriate on-resistance. The Si4410DY is a good option for this circuit.

To change Q1 from the IRF530 to the Si4410DY, follow these steps:

1. Double click the MOSFET symbol.
   Result: The Extract MOSFET Parameters dialog appears.
   
2. Click the Select button to the right of the SPICE Model field.
3. In the Search field, type Si4410DY.
   Result: Si4410DY is the only selection in the Installed SPICE models list.
4. Highlight Si4410DY, and then click OK.
5. Click Extract.
   Result: The SPICE model for Q1 changes to Si4410DY.

To change the Diode to use the built-in IDEAL device, follow these steps:

1. Double click the D1 symbol.
   Result: The Extract Diode : D1 Parameters dialog.
   
2. Click the Select button to the right of the SPICE Model field.
3. In the Search field, type ID.
   Result: IDEAL is the only selection in the Installed SPICE models list.
4. Highlight IDEAL, and then click OK.
5. Click Extract.
   Result: The Diode symbol now appears with the IDEAL label.

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2.2.5  Configure the Waveform Generator

The waveform generator is a flexible device that can represent a number of periodic waveform types. To drive the MOSFET Q1, you need a pulse generator with a specified pulse width, frequency, and amplitude.

 To set up the Waveform Generator as a Pulse source, follow these steps:

1. Double click the waveform generator symbol.
   Result: The Edit Waveform dialog appears.
2. On the right side of the dialog in the Wave Shape section, select the Pulse radio button.
3. In the middle column at the top, change Frequency to 500k and Duty Cycle to 11.
4. In the first column near the bottom of the dialog, change Pulse to 5.

   Note: As you make each change, the corresponding values are recalculated but the recalculated values do not appear until you click in another text field to make the next change.
   

5. Click Ok to save the new parameter values.

The design is now at a point where you can start your first simulations and then begin further optimization.

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2.2.6  Saving your Schematic

To save your schematic, follow these steps:

1. Select File ▶ Save As.
2. Navigate to your working directory where you are saving your schematics.
3. Name the file 2_my_buck_converter.sxsch.

A schematic saved at this state can be downloaded here:
2_SIMPLIS_tutorial_buck_converter.sxsch.

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