SIMPLIS Simulation Tames Analysis of Stability, Transient Response, and Startup For DC-DC Converters

by Timothy Hegarty, National Semiconductor, Tucson, Ariz., How2Power Today, Aug 19 2010

Focus:
This article demonstrates a SIMPLIS circuit simulation of a non-isolated dc-dc converter that allows the designer to explore the converter's load-transient behavior, control-loop stability and output-voltage startup characteristic. The simulation is based on a full time-domain, non-linear, switching model of the converter. Aside from the simplicity and flexibility of the simulation process described here, its convenience renders it viable for everyday use by the practicing power electronics engineer. With this approach, there's no need to derive averaged models of the converter or identify the current-loop sampling gain contribution. This simulation method accommodates circuit non-idealities, including error amplifier finite gain-bandwidth characteristic and switch minimum on-time constraints, using small-signal ac analysis simulation to produce meaningful bode plot results up to half the switching frequency. The output voltage waveform in response to a load transient can then be simply determined with time-domain simulation using the same model. The key benchmarks of output transient performance-peak deviation and settling time-are readily obtained. Finally, with this simulation method, the startup characteristic can be scrutinized as it pertains to soft-start time, output voltage waveform monotonicity, and pre-bias startup compatibility.

What you’ll learn:

• How to use the SIMPLIS simulation to analyze the load-transient behavior, control-loop stability and output-voltage startup characteristic of a nonisolated dc-dc converter

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