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From: Bill Sloman <bill.sloman@ieee.org>
Newsgroups: sci.electronics.design
Subject: Re: fast NPN in LT Spice
Date: Sat, 8 Jun 2024 03:29:11 +1000
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On 7/06/2024 11:24 pm, legg wrote:
> On Fri, 7 Jun 2024 14:03:16 +1000, Bill Sloman <bill.sloman@ieee.org>
> wrote:
> 
>> On 7/06/2024 4:05 am, legg wrote:
>>> On Thu, 6 Jun 2024 23:18:12 +1000, Bill Sloman <bill.sloman@ieee.org>
>>> wrote:
>>>
>>>> On 6/06/2024 1:46 pm, legg wrote:

<snip>

> That's sort of what I'm talking about. You choose a part, you choose a
> model, you choose a parameter that allows a model to simulate
> performance more accurately. You choose a circuit configuration
> with component values.

You mostly can't chose an EBIC model because the manufacturers treat 
them as "commercial in confidence".

Gummel-Poon isn't as good, but it's mostly adequate.

>  From the larger spreadsheet, you see models for 'similar devices
> varying widely in performance in a particular circuit configuration.
> 
> So what is it, in the model, or in the circuit configuration, that
> allows such a wide variation in performance. What parameter is a
> true predictor? What weakness in the circuit is the wild card?

Silly question. Gummel-Poon doesn't model inverted bipolar transistor 
operation particularly well, but if you want anything else you will have 
measure the device parameters for yourself, and nobody here has ever 
claimed to have done that.

> Looking for understanding or beneficial increase in knowledge here.
> Not pushing or pulling the benefits or disadvantages of modeling
> or breadboarding - already have pretty fixed opinions about that.

Do try to understand what practical circuit designers actually do.

I've never seen anybody set up a "spreadsheet" of transistor models.

The process is mostly working out what you can do with what you can get.

The models aren't perfect, and individual devices aren't identical, so 
coping with production variation is part of the job. Some parts are 
sorted by the manufacturer after production, which gives you 
funny-looking parameter distributions.

-- 
Bill Sloman, Sydney




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