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From: legg <legg@nospam.magma.ca>
Newsgroups: sci.electronics.design
Subject: Re: fast NPN in LT Spice
Date: Tue, 11 Jun 2024 11:27:20 -0400
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On Wed, 12 Jun 2024 00:35:59 +1000, Bill Sloman <bill.sloman@ieee.org>
wrote:

>On 11/06/2024 7:27 am, legg wrote:
>> 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>
>
>> 
>> Right, I see Q2 normally inverted.
>> 
>> C2 seems unneccessarily loaded.
>
>If you are talking about the .asc file I posted on the 3rd June, Q2 
>isn't "normally inverted" - its mostly on, and it gets turned off for 
>the 30nsec in which the stretched pulse is being generated. Inverted 
>operation of a bipolar transistor is usually taken to mean running 
>current through them in the opposite direction than is seen in normal 
>operation.

Just returning to this, trying to see what determines the switch from 
non-switching to astable operation (ECLTN0E - ECLTN0D). Misreading a 
current and voltage waveform with similar color coding.
>
>C2 isn't carrying any current worth worrying about. It stabilises the 
>voltage at the base of Q3 against the base current drawn when the output 
>pulse is turned on and turned off, -6.7mA when it is turned on an +2mA 
>when it is turned off, and holds the voltage excursion down to 3.7mV, 
>not that I ever bothered working this out.
>
>If you want to discuss when the circuit does and how it does it, feel 
>free, but this wasn't a good start.
>
>-- 
>Bill Sloman, Sydney

Not so much interested in the circuit, as its reaction to model 
parameters presented by similar devices.

Not Beta, Tr or Tf in this case.

RL