Re: New convergence failure (was Re: [Help-gnucap] Several problems: convergence failure...)

[al davis]

On Monday 01 March 2010, Rubén Gómez Antolí wrote:
> Sorry about repeat topic, but I'd fall in a nightmare with
>  this circuit  and his evolution.
> 
> If is possible that there are a fail in design because I
>  haven't correct  output of buck chopper (1.5 V instead 1V,
>  Ngspice runs circuit :-/ ), but I can't found the "bug".
> 
> I note that in Ngspice output there are too much "noise",
>  that I think  is no normal.
> 

I can't run it .. there are pieces missing.

Spice time step control and convergence checking is often not 
strict enough.  Sometimes it accepts results that are wrong.

Here are a few ideas ...

Breakdown doesn't work with the native diode model.  Try the one 
in models-spice3f5 instead and see if that helps.

Try "option noincmode nobypass".

Try setting gmin larger.

Try adding a resistor across the diodes.

Try adding a switch, with the control port across a pair of 
nodes that you think are causing trouble.  Leave the output 
(switched resistor) unconnected.

Try "option method=euler" 
or "option method=gear"