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Comment by oxinabox | Hacker News Reader

This seems very promising to me One big part of circuit simulation is solving differential equations. That's the whole inducer, resistor, capacitor thing. Julia has hands down the best toolkit for differential equation solving. Most circuit simulators today are going to be using old methods invented in the 60's-80's. Neglecting the state of the art developments.

Someone made a blog post recently comparing the time to simulate with LTSpice vs writng and solving the system in Julia https://klaff.github.io/LTSvDEQ_1.jl.html this is a very simple circuit, and they still got a 100x speed up. Sure that is neglecting the time it takes to actually extract the differnetial equetion from the circuit. But from what i hear that kind of thing is something this DARPA project will be working on. And sure LTSpice isn't state of the art. But still I find this indicative and promising.

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As someone that actually uses LTSpice I’ve never considered speed to be an issue. The main draws for it are

1. It’s free unlike Altium addons or orcad p-spice

2. Graphical, I’m happy to code things but code literacy varies widely among EEs. Much easier to share results when it looks like a schematic

3. Good enough component library. The time spent finding and inputting component parameters are gonna be way bigger than any savings on the actual computation

I mostly work on small embedded systems boards and use simulation to probe behavior of analog sub systems I’m concerned about, rather than simulating the whole board. Maybe more complex designs get more like CFD models where computation time is measured in hours or days. Would love to see someone use this as a backend for an alternative to the major spice programs, LTSpice UI isn’t exactly pleasant, and is unusable on Mac so it wouldn’t take a whole lot to get me to switch.

1. yeah these are super expensive. Even the cheaper ones are close to a grand a liscense 2. definately got to have a front-end. Writing netlist by hand is suffering. 3. Interestingly (to me) the components are more or less portable between them. With only a little manual writing i have translated components from ORCAd p-spice, to ISpice, to LTSpice. No idea on the liscensing for that. (I suspect the IC manufacturers produce these)

I think speed is very much a question of what kind of thing you are doing. I agree it often doesn't matter. and without your 3 points, it certainly doesn't matter

LTSpice is my go-to circuit simulator, but I have spent weeks of my waking life waiting on it to run simulations. My current demon is simulating a 1 MW DC power supply to validate current output smoothing solutions in low load scenarios. The topology is a delta-delta and delta-wye transformer, each feeding a summing bridge rectifier, the two rectifiers have their negative legs tied together and the positive legs are the outputs.

I only simulate one pulse (about 3 ms), but the simulation takes minutes to resolve the inrush. Tuning circuit impedances to match measurement is a real pain. At this point I'm just going to take many more direct measurements. If it was quick I would have written a script to scan through unknown parameters to maximize correlation with measurements, but that isn't reasonable when the simulation fails after several minutes of trying for most values.

Oof that's rough. Don't know if it can handle your topology but have you tried LTPowerCAD or TIs equivalent? They did the job when I was doing a boost converter design but I don't remember how capable they were for more complex tasks.

The problem is a lot of the models you use are black box characterized models and not differential equations. I don't mean Julia won't speed things up a lot and won't be helpful but your point about modern sim tools using old techniques is not true. Simulation RCL in semiconductors is a huge business where customers have been paying a lot for faster solutions.

fair enough. I can't say i've seen inside how things things are made. Julia definately has cutting edge for DEs. I doublt LTSpice does, but ORCAD etc might.

Not only that, but the LTSpice solution was incorrect, and the Julia solution was correct.

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