Re: gEDA-user: problem to simulate an astable multivibrator with uA741 opamp

[John Doty <jpd@xxxxxxxxx>]

On Apr 15, 2009, at 8:55 AM, joseda wrote:

>
> That was the trick! I fixed by adding a new voltage source of -15V  
> (i called
> Vee)
>
> But why is not -Vcc the same as Vcc multiplied by -1?

Vcc is only a name of a network.

> Vcc is 15V

V(Vcc) is 15V. Vcc is just a name. Now in *some* cases, ngspice will  
assume that you mean V(Vcc) when you enter Vcc. Not all SPICE  
dialects do this, and ngspice only does this is certain contexts.  
This is arguably a confusing misfeature. For one thing, it means it's  
a bad idea to use characters like "-" in ngspice netnames.

> so -Vcc should be -15 V but it doesn't work this way!!

To what voltage source is -Vcc connected to make it -15V? I see no  
such source in your circuit.

> Anyway, thanks!
>
>
> You have a node named "-Vcc". You haven't attached this node to
> anything outside the opamp. Presumably you intended to attach a
> negative power supply. The opamp model contains a current source
> attached to this node, so letting it float makes rather high voltages.
>
> John Doty              Noqsi Aerospace, Ltd.
> http://www.noqsi.com/
> jpd@xxxxxxxxx
>
>
> -- 
> View this message in context: http://www.nabble.com/problem-to- 
> simulate-an-astable-multivibrator-with-uA741-opamp- 
> tp23057811p23060560.html
> Sent from the gEDA - User mailing list archive at Nabble.com.
>
>
>
> _______________________________________________
> geda-user mailing list
> geda-user@xxxxxxxxxxxxxx
> http://www.seul.org/cgi-bin/mailman/listinfo/geda-user
>

John Doty              Noqsi Aerospace, Ltd.
http://www.noqsi.com/
jpd@xxxxxxxxx




_______________________________________________
geda-user mailing list
geda-user@xxxxxxxxxxxxxx
http://www.seul.org/cgi-bin/mailman/listinfo/geda-user