[sdiy] LTSpice macromodell help

Harry Bissell harrybissell at wowway.com
Thu Apr 14 18:26:43 CEST 2011


I've found the voltage controlled switches to be a bit cranky...  you need to change
a lot of parameters to make them work as you would expect. Of special not, there is
an inductance parameter that can be REAL trouble if you make the switch open resistance
real high and then open the switch real fast... the resulting overshoot can clobber the rest of the simulation.

I usually spend a lot of time playing with the actual components in a separate circuit to see how they 'work' 
before using them in a simulation.

H^) harry


----- Original Message -----
From: Dave Manley <dlmanley at sonic.net>
To: Synth-diy at synth-diy.org
Sent: Thu, 14 Apr 2011 11:23:11 -0400 (EDT)
Subject: Re: [sdiy] LTSpice macromodell help

Could this be done with a pair of voltage controlled switches (VCSW)?
I've seen them in the library but haven't used them.


On 4/14/2011 7:03 AM, Harry Bissell wrote:
> I'm trying to make a perfect comparator. So I have a voltage-controlled voltage source
> with a gain of 1e6, followed by a clamp.  The diodes and voltage sources didn't work too well,
> the currents become astronomical. The diode thing works real well at ot near the supply rails, though.
>
> Thanks for the article, its a good read.
>
> H^) harry
>
>
>
> ----- Original Message -----
> From: Tim Stinchcombe<tim102 at tstinchcombe.freeserve.co.uk>
> To: 'Harry Bissell'<harrybissell at wowway.com>, 'synthdiy'<Synth-diy at synth-diy.org>
> Sent: Wed, 13 Apr 2011 17:32:05 -0400 (EDT)
> Subject: RE: [sdiy] LTSpice macromodell help
>
> Darn! Seconds after I hit the 'send' button I re-read your message and
> realized that article probably _doesn't_ do what you were asking!
>
> So, I pulled Connelly&  Choi off the shelf, and sure enough they use the
> diodes+voltage sources method in their op amp macromodel, using a very ideal
> diode model:
>
> .model dx d (n=.001)
>
> and then diodes using 'dx' to clamp to the positive and negative rail
> respectively. (Hopefully this makes sense this time...).
>
> Tim
> __________________________________________________________
> Tim Stinchcombe
>
> Cheltenham, Glos, UK
> email: tim102 at tstinchcombe.freeserve.co.uk
> www.timstinchcombe.co.uk
>
>
>> -----Original Message-----
>> From: Tim Stinchcombe [mailto:tim102 at tstinchcombe.freeserve.co.uk]
>> Sent: 13 April 2011 22:22
>> To: 'Harry Bissell'; 'synthdiy'
>> Subject: RE: [sdiy] LTSpice macromodell help
>>
>>
>> As well as tanh already suggested, I think the 'arctan'
>> expression used in this nice little article does the job
>> tolerably well too:
>>
>> <http://www.edn.com/article/493732-Modular_macromodeling_techn
> iques_for_Spice_simulators.php>
>
> PDF version:
>
> http://www.edn.com/contents/images/198891.pdf
>
> Tim
> __________________________________________________________
> Tim Stinchcombe
>
> Cheltenham, Glos, UK
> email: tim102 at tstinchcombe.freeserve.co.uk
> www.timstinchcombe.co.uk
>
>
>> -----Original Message-----
>> From: synth-diy-bounces at dropmix.xs4all.nl
>> [mailto:synth-diy-bounces at dropmix.xs4all.nl] On Behalf Of
>> Harry Bissell
>> Sent: 13 April 2011 16:48
>> To: synthdiy
>> Subject: [sdiy] LTSpice macromodell help
>>
>>
>>
>> Hi all... yes its synth-related
>>
>> I'm trying to come up with a macromodel of a voltage limiter
>> circuit. Electronic Workbench includes such a device, LTspice
>> does not.
>>
>> The object would be to limit input voltages to a range
>> between Vpos and Vneg that I would set. Using a series
>> resistor, two diodes, and two voltage sources is a crude way
>> to do it. I'm looking for something much more elegant.
>>
>> Any takers ???
>>
>> H^) harry
>> _______________________________________________
>> Synth-diy mailing list
>> Synth-diy at synth-diy.org
>> http://synth-diy.org/mailman/listinfo/synth-diy
>>
>>
>
>
>
>
>

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-- 
Harry Bissell & Nora Abdullah 4eva


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