Conclusions

After completing the tutorial, you have a closed-loop synchronous buck converter model which uses a hierarchical schematic for the compensator. The compensator parameter values are calculated in the F11 window of the compensator from desired poles and zeros, effectively abstracting the design.

This model runs in all three analysis modes: POP, AC, and transient. By running all three analyses, you can verify the large- and small-signal stability of the converter.

Summary of Key Concepts

Following are the key concepts presented in the tutorial.

The SIMPLIS Simulator

  • SIMPLIS is a time-domain simulator for all three analyses modes: POP, AC, and transient.
  • The POP analysis finds the switching steady-state operating point of the circuit.
  • The AC analysis finds the small-signal response of the circuit perturbed around the switching steady-state operating point found with the POP analysis.
  • The AC analysis is performed in the time domain on the full switching PWL model; therefore, all non-linearities are included in the AC analysis.
  • A successful POP analysis is required to run an AC analysis.
  • During a POP/transient simulation, the transient simulation begins with the initial conditions found during a POP analysis.

Modeling

  • All models used in SIMPLIS are Piecewise Linear (PWL).
  • MOSFETs and diodes are represented by collections of PWL devices with the parameters often calculated by built-in parameter extraction routines.
  • Multi-level models can represent different schematic views depending on the model level. Built-in multi-level models include semiconductors, MOSFET drivers, inductors, capacitors, and a parameterized OpAmp.
  • An ideal synchronous rectifier can be made using a user-defined diode. The resulting PWL resistor model has a zero-volt forward voltage and two segments, one each for the on and off resistances

Graphing and Measurements

  • You can control where curves appear on the waveform viewer by changing properties of the fixed probe symbol.
  • Measurements can be made on output curves either interactively with the waveform viewer menus or automatically by adding the measurement definition to the fixed probes on the schematic.

Follow-on Work and Suggested Reading

Although the converter model at the end of the tutorial is relatively simple, it provides a good foundation on which to expand the model. The Advanced SIMPLIS Training course picks up where this tutorial leaves off. The Advanced SIMPLIS Training course, which is presented several times per year in different locations, provides expert level material in a tutorial format. You can access the Advanced SIMPLIS Training Course material here: Advanced SIMPLIS Training Course Material.

Suggested Exercises

The tutorial circuit is a good starting point for further exercises. A few suggested exercises are listed below.

  • Modify the schematic to use hierarchical schematic components for all functional blocks.
  • Modify the circuit to use a MOSFET for the synchronous rectifier, adding a driver and drive logic.
  • Add current limiting. Examine the converter behavior when in current limit using a POP analysis.
  • Explore different control techniques. Use hierarchical blocks to maximize reuse and to change between different control methods.
  • Measure the efficiency of the converter by changing the MOSFET model level to level 2 and verify the switching losses for the circuit.
  • Experiment with changing the MOSFET drive characteristics. Remove the gate resistor and use a level 1 or level 2 MOSFET driver to tailor the gate drive current.
  • Change the compensator to use parameters passed into the component from the parent schematic. Parameterization is described in the Advanced SIMPLIS Training Course: Module 5 - Parameterization topic.