Aug 17 2009 3:31PM
Linear Technology Corporation employs software guru Mike Engelhardt. Mike, better known to we Silicon Valley denizens as Panama Mike due to his styling headwear, developed a SPICE package sometimes branded as SwitcherCAD, but more properly called LTspice. Mike has announced the world tour of his LTspice seminar regarding this free software. I had a PSpice developer tell me once that any idiot can hang a schematic-entry front end on Berkeley SPICE, the real trick and most of the effort at PSpice was to get things to converge. Since SPICE is all about taking a guess and then ensuring that the guess is closer to the solution, it is not surprising that SPICE fails to converge in a world full of diodes and base-emitter junctions and other non-linear devices that makes guessing in software pretty challenging. Magnetic components make even more convergence problems. That is the amazing contribution that Engelhardt has made. Not only does LTspice tend to converge, it converges fine even when dealing with switching power supplies that use magnetic components. I think it is safe to say that it was Mike who made the world believe that you can reliably simulate switching power supplies. A little bit of Silicon Valley gossip— Mike thinks that the modeling of power supply chips is so critical, he does those himself, whereas things like op amps, he lets the product groups do the model.
I want to give another shout out to a great book on SPICE, Inside Spice: Overcoming the Obstacles of Circuit Simulation, by Ron Kielkowski, McGraw-Hill, January 1994. Matt Berggren at Altium recommended this out-of-print book to me and it is a great resource, as I pointed out in my field solver article. You might want to read this book before you go to Mike’s seminar. As the book is out of print, you may have to buy it used like I did. There are two editions—I paid 30 bucks or so for the first edition. The second edition goes for 130 bucks, a little too pricey for me. I have to admit the book paid for itself in 20 seconds when Kielkowski pointed out that SPICE stands for “Simulation Program with Integrated Circuit Emphasis” so wouldn’t you expect to change all the defaults when you are using it to simulate a PCB system instead of an IC?
If you want to use SPICE, realize that it can give bad answers, even LTspice, if you feed it bad models. Still, if you are inexperienced, you might want to model your circuits before you breadboard them, and sorry, you cannot fully trust any simulation for board-level circuits. You do have to build a prototype before releasing it to production, no matter how much SPICE you did on it. This ain’t college and this ain’t reality TV.
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