SIMPLIS Tutorial

3.2  Set up a POP Analysis

In this section, you will set up a SIMPLIS Periodic Operating Point (POP) analysis to examine the steady-state behavior of this converter. This requires that you add a SIMPLIS custom subcircuit - a POP trigger.

• This POP trigger subcircuit is unique to SIMPLIS and contains a reference voltage and comparator.
• The POP trigger device tells SIMPLIS which top-level node to use to detect the beginning of each new POP period during the Periodic Operating Point analysis.
• This schematic node should trigger the POP trigger to switch at the lowest frequency at which the entire system is periodic;  in other words, the lowest frequency at which every energy-storage element in the system exhibits periodic behavior.

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3.2.1  Add a POP Trigger to the Schematic

To add a POP trigger, follow these steps:

1. To change the focus from the Graph window to  the Schematic editor, type Ctrl+T.
2. From the Parts Selector, click the + in front of Analog Functions.
3. In the expanded list, double click Pop Trigger.
4. Place the cross hair directly below the diode, and click the left mouse button to place the POP trigger.

   Note: If you need to move the trigger down after you place it, press and hold the left mouse button on the symbol and then drag the symbol lower on the schematic.

5. To use the switching node as the periodic source, follow these steps to connect the wires:
   1. Make sure that the trigger is deselected, and place the cursor at the end of the line on the left side of the trigger.
      Result: The cursor changes from a cross hair to a pencil.
   2. Click the left mouse button, and draw a short horizontal line to the left.
   3. Click the left mouse button again to create a corner, and extend the wire to the line that connects to the switching node.
   4. Click the left mouse button again to make the connection and then click the right mouse button to finish the wire.
      Result: The schematic should now look like this:
      
6. To save this version of the schematic, select  File ▶ Save from the menu bar in the schematic editor.
   Note: You can also open this version of the schematic at this link: 3_SIMPLIS_tutorial_buck_converter.sxsch.

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3.2.2  Set up the POP Analysis

To set up the POP analysis directives, follow these steps:

1. From the menu bar in the Schematic editor, select Simulator ▶ Choose Analysis....
   Result: The Choose SIMPLIS Analysis dialog appears.
2. Click the Periodic Operating Point tab.
3. In the Select analysis section on the upper right side of the dialog box, check POP and uncheck Transient.
4. To configure the simulator to use the schematic symbol for the POP trigger, go to the Triggering section at the top of the left side of the dialog box and click the check box in front of Use "POP Trigger"  schematic device.  
5. To specify the maximum switching period for your circuit, go to the Conditions section of the dialog and change the Max. period value to 2.2μs, which is 110% of your steady-state period.
   Important: The maximum-period parameter limits the solution space in which POP searches for a steady state condition. The maximum period parameter must be greater than the switching period but it is recommended that it not be set to more than two times the switching period.
   

6. After you enter the analysis directive parameters, do one of the following:
   Click the Run button.
   OR
   Click Ok to save the data and press the shortcut key F9 to run the simulation.
   Result: The graph window opens with the steady-state waveforms for your converter. In this window, the probed waveforms for VOUT, SW, and IL are displayed for five periodic switching cycles.
   

   Note: In Section 4 of this tutorial, you will learn more about manipulating the output and making the graph easier to read.

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3.2.3  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 3_my_buck_converter.sxsch.

A schematic saved at this state can be downloaded here: 3_SIMPLIS_tutorial_buck_converter.sxsch.

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