>
>> From: owner-amps@contesting.com [mailto:owner-amps@contesting.com]On
>> Behalf Of measures
>> Sent: Sunday, September 10, 2000 4:00 PM
>> To: AMPS
>> Subject: RE: [AMPS] Blown TL922A... What to do?
>
>> >Clearly there are limits to the fidelity of software models. But if a model
>> >oscillates with a realistic set of parameters, then oscillation is a
>> >practical reality. And if no set of reasonable parameters can be found to
>> >support oscillation, then for practical purposes the circuit being modeled
>> >does not oscillate.
>>
>> Using such software, it was determined that the 8877 is likely to be able
>> to oscillate above 100MHz. In my opinion, corrective measures are
>> indicated.
>
>"is likely to be able to oscillate" is a subjective assessment; we seek
>objective, repeatable proof. Either the model oscillates, or it doesn't.
>
So at 99.999MHz, no oscillation. At 100.000MHz oscillation. . In my
experience parasitics tend to be not very predictable. My guess is that
the di/dt of the DC current change the creates the VHF damped wave
ringing in the anode circuit is a factor.
>> >Evaluating the effectiveness of suppressor circuits is a
>> >similarly-objective excersize.
>> >
>> The intermittent nature of VHF parasites makes this difficult at best.
>
>If the model oscillates, it will do so repeatably, permitting an objective
>evaluation of suppressor techniques.
>
Fantasyland.
>> >I suspect that neither combatant is truly interested in resolving the
>> >underlying technical issue;
>>
>> ? not a good bet.
>>
>
>Fine. Publish a model that, with reasonable parameter values in a commercial
>circuit simulator of your choice, repeatably oscillates.
>
The quarry is too intermittent.
>
later, Dave
- Rich..., 805.386.3734, www.vcnet.com/measures.
end
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