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From: legg <legg@nospam.magma.ca>
Newsgroups: sci.electronics.design
Subject: Re: fast NPN in LT Spice
Date: Mon, 10 Jun 2024 17:27:59 -0400
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On Sat, 8 Jun 2024 03:29:11 +1000, Bill Sloman <bill.sloman@ieee.org>
wrote:

>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

Right, I see Q2 normally inverted.

C2 seems unneccessarily loaded.

RL