[Qucs-help] jacobian singulars everywhere..

[Z <en...@hd...>]

Hi again,

This time I connected an AC power source to a rectifier bridge, and 2 
blue 20 mA LEDs in series (from library) as load. Transient simulation 
runs propely at 300 mW AC source power, but I get a Jacobian singular at 
301 mW.

At 250 mW it was ok until I connected an 1 pF capacitor. (actually, it 
is a placeholder for a varistor)

Sometimes the simulation becomes ok, if I change the number of 
timesteps, or the time interval of the simulation. It is more stable, if 
I start simulation from 0 msec.

If I increase the capacitance to 1 uF, the simulation is stable. 
According to the diagrams, the LED current becomes stable a little bit 
below 1 mA.

I would like to know, how I could eliminate these Jacobian singulars. I 
would run the simulation above 300 mW and below 1 uF..

I have a similar circuit with 350 mA leds, 3W power source and 
capacitors around 1 mF, and there I have the same errors in the region 
500..2000 uF. Any help appreciated.

Thank You for your reply in advance.

Szalai Zoltán