Circuit Simulation Tools

(Some excerpts from discussion on LinkedIn)

I think a typical schematic design consists of 3 stages:

1. System level simulation
2. Schematic concept proving
3. Detailed analysis

Number 1 is testing the principle of a design on “block-diagram” level – no specific components/models, just functional blocks or equations. Not much choice of tools here: Matlab/Simulink/SimPowerSystems or PLECS (which is basically Simulink). Just use what your company purchased.

Let me jump to number 3: a huge selection of tools with wide ranges of features, performance, and prices (from free LTSpice to “multi-zeroes” Saber) are available, and almost all are SPICE-based. The best choice would be the one a) with the most accurate models, or at least ones you trust, b) that can perform all types of schematic analysis required by the company’s development process, and c) that can be integrated with other tools used by the company, such as PCB design, etc. In my opinion, in most companies engineers do not have much, if any, influence here. Depending on who makes a decision, the tool is selected based on either price (the higher the better :) or “shiny” ads and presentations. Maybe this is fine: since just ONE official tool for the company has to be selected, there will always be people who like it and who don’t. C’est la vie.

Number 2, I think, is the most important stage of a development. It is supposed to provide the right concept of a design prior to detailed analysis. Verifying your schematic idea with very simple “ideal” models you can catch and fix many essential schematic problems much quicker and easier, thus saving time, money, etc. And I believe that a “concept proving” tool MUST be personal engineer’s choice: the more comfortable the tool is to work with, the more efficient it is. I don’t think it’s going to be a problem for the company if engineers are using different tools – such a tool should be reasonably simple and cheap, no integration is needed, no models and libraries to support.

What candidates do we have on the market? Not much. I’m not considering SPICE-based simulators: even LTSpice, which is surprisingly very fast, failed at several simple schematics with ideal components. (And my personal opinion: the LTSpice interface is the worst I’ve ever seen). PSIM deals with ideal components, is fast, and provides AC response of switching circuits, which is good. But it also failed my tests with ideal components. SIMPLIS – I have not tested it yet. And, of course, NL5 – that’s why I’m writing all this :). By the way, although it is new to the public, the core of the NL algorithm was developed in the late 80s, and earlier DOS/Windows versions have been extensively used by a limited number of users since the 90s. It has been tested and proven, unlike many products announced for sale before they’re actually completed.