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Better power MOSFET models in LTSpice
Better power MOSFET models in LTSpice
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Old 26th December 2014, 05:48 AM   #31
bimo is offline bimo  Indonesia
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Quote:
Originally Posted by keantoken View Post
If you were using an old NMOS/PMOS model, upgrading to VDMOS will result in higher distortion because the old models give much too low gate capacitance.
I always use Bob Cordell's models if available and your models, too.
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Old 26th December 2014, 08:42 AM   #32
davidsrsb is offline davidsrsb  Malaysia
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Unfortunately IRF540s from the various vendors are not 100% the same. They use different manufacturing processes and cell design
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Old 26th December 2014, 09:26 AM   #33
dadod is offline dadod  Croatia
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Originally Posted by bimo View Post
I have almost same harmonic profile like yours (with and without ksubthres models). But THD rise with ksubthres models. My amp is VFA with Hitachi VAS.
I've seen THD drop at 20kHz and no change at 1kHz, but in both cases harmonic profile was better. I use OIC and that could be reason for THD20k drop.
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Old 26th December 2014, 10:24 AM   #34
wintermute is offline wintermute  Australia
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Better power MOSFET models in LTSpice
Quote:
Originally Posted by keantoken View Post
I made a mistake when starting this thread, I said FET and not MOSFET. I changed the references in the post but I wasn't able to edit the thread title. The improvements are to the MOSFET model, so won't work for Jfet models.
and as if by magic the thread title changed
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Old 26th December 2014, 11:29 AM   #35
Bob Cordell is offline Bob Cordell  United States
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Quote:
Originally Posted by keantoken View Post
Okay guys, it would help if you could post links or attach datasheets or measurements with clear, precise plots of Gm and Id vs. Vgs. I got the IRF540 to model Gm within 1% above 3A, but below that the graph just doesn't have enough data and the digitizer can't extract it without significant errors.

Also, ST datasheet has different curves than the Fairchild datasheet which has different curves than the IR datasheet, etc etc. How do I choose which one to model? I guess it just depends on which datasheet gives the best data...
In general I've depended on measurements of actual power MOSFET devices to get models with decent performance at low current, especially for the subthreshold region. It doesn't take many datapoints in the subthreshold region to get what you need, because the exponential behavior there is fairly well understood. The subthreshold slope just needs to be inferred with some confidence. Vgs measurements at 10uA, 100uA, 1mA and 10mA is probably plenty. Vgs will usually change about 200-500mV per decade. I have found that a conventional VDMOS model that does a decent job of modeling above subthreshold can be made pretty accurate by just adding a value of ksubthres that just brings up the low-end current up to the proper subthreshold slope.

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Old 26th December 2014, 09:00 PM   #36
keantoken is online now keantoken  United States
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Originally Posted by wintermute View Post
and as if by magic the thread title changed
Thanks!
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Old 26th December 2014, 10:11 PM   #37
keantoken is online now keantoken  United States
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When using the new models has anyone noticed a simulation taking more time? Is the new model significantly slower, or maybe faster?
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Old 27th December 2014, 05:32 AM   #38
dadod is offline dadod  Croatia
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Quote:
Originally Posted by keantoken View Post
When using the new models has anyone noticed a simulation taking more time? Is the new model significantly slower, or maybe faster?
Maybe a bit slower the new models, but not significantly.
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Old 3rd January 2015, 04:11 AM   #39
lhquam is offline lhquam  United States
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By coincidence I have been measuring IRFP240 and IRFP9240 FETs recently in the low current region (< 1A) and found them to behave quite differently than predicted by the standard VDMOS model. For the 20mA to 600mA range, Id behaved more like (Vgs-Vth)^3.3. I stumbled onto the EKV model and was able to make that work, but yesterday I discovered this thread and the new LTSpice version with Ksubthres added to the VDMOS model. I think it will solve many simulation issues I have been wrestling with. Many thanks to Mike Engelhart.
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Old 3rd January 2015, 04:31 AM   #40
keantoken is online now keantoken  United States
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Cordell made some new 240/9240 models:

http://www.diyaudio.com/forums/softw...ml#post4162193

Can you check them with your data to see if they agree with your measurements?
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