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Is there something wrong with PMOS model in the LTSpice XVII?

"Jim Thompson" wrote in message news: snipped-for-privacy@4ax.com...

Well, that's what the existing one does, in a sense, as I understand it. (You charge up a nonlinear capacitor, and it discharges on reverse. Turn-off is "triggered" when the excess capacitance becomes small enough not to care.)

(Huh...Also, you should know better than to use words like "trigger", Mr. all-continuous-derivatives!)

But that doesn't capture dynamic voltages (namely, the transport stuff Phil is concerned with), which has a more inductive aspect, but a non-conservative (dissipative, lossy) one.

*Shrug*, I always put an R||L in series with the thing, approximating the datasheet's spec (when provided), and that looked right enough. The curve isn't actually linear, but usually sub-linear... almost sqrt(dI/dt), even (ta-da, diffusion magic!). But a linear approximation is more than good enough for a switching supply, where the dI/dt is well defined, consistent and modest.

Tim

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Seven Transistor Labs, LLC 
Electrical Engineering Consultation and Contract Design 
Website: http://seventransistorlabs.com
Reply to
Tim Williams
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Well, I wouldn't, but not because of mathematical reasons, but practical ones.

There's little point in modeling an SRD, because I wouldn't expect one to actually be well enough specified to match its model, anyway. You're also talking bandwidths where you need a full E&M model of the circuit, which means you need to lay it out first. Catch-22.

An expensive Catch-22 at that -- once you've mortgaged half of your house to buy the Ansys tool chain!

C'mon Phil, stop sucking on margaritas and kicking sand (by which I mean, trivially pathological cases) in our faces. ;)

A much more practical case for diode modeling: switching supply rectification and snubbing. I've yet to build one where the diodes exhibited snap recovery. The V, I and t are all very well constrained in this case. That's with V and I bounded by datasheet limits (Vrrm and Isurge), and dI/dt maybe 10 A/ns worst case. Oh, and say it's pretty gross, like 20% accuracy.

Is this proscribed well enough now? What's the Big-Oh on the number of internal states?

Tim

--
Seven Transistor Labs, LLC 
Electrical Engineering Consultation and Contract Design 
Website: http://seventransistorlabs.com
Reply to
Tim Williams

The nonlinear capacitor is the key

(:

Easy enough as well.

Indeed. I don't know why Phil got a hair so far up his butt he can't retrieve it. I guess it's the old adage, don't ever try to tell a PhD he's wrong ;-) ...Jim Thompson

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| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    | 
| STV, Queen Creek, AZ 85142    Skype: skypeanalog |             | 
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  | 
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     Thinking outside the box... producing elegant solutions.
Reply to
Jim Thompson

I have now simulated two designs from two earlier writers. They both work. But when looking for a way to attach Star-leds, I found led-supplies which are cheaper, smaller and better than what I was building. I of course new that this is the way it is put it is still frustrating.

After I have attached the leds I'll start building the switcher.

Reply to
LM

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