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
- 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.
- 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.
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
- Modify the circuit to use a MOSFET for the synchronous rectifier, adding a driver and
- Add current limiting. Examine the converter behavior when in current limit using a POP
- 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.