[sdiy] LTSpice macromodell help

[Harry Bissell]

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 dropmix.xs4all.nl>
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
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> Synth-diy at dropmix.xs4all.nl
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> 
> 





-- 
Harry Bissell & Nora Abdullah 4eva