Spice; time step to small error

[kinarfi]

How do I correct a problem of time step to small. asc attached
Thanks
Kinarfi

 

[crutschow]

I can't simulate your circuit since you are using models I don't have.

If you go to the SPICE tab in the control panel there are various options you might try changing.
Try trapezoidal or Gear instead of modified trap for the Integration Method.
Increase all the tolerance values by a factor of 10, e.g. Voltol to 1e-005 instead of 1e-006.

In the Transient simulation command:
Check "Start external DC supply voltages at 0V".
Check "Skip initial operating point solution"

 

[ericgibbs]

hi,
I have also tried to run it in LTS, but there are so many missing models.

The LM2907 section runs OK when copied to another asc file.

 

[kinarfi]

Gentlemen,
Thanks for the help, I guess my computer or spice doesn't like the LM324- nor the lm324_ subs I have, I changed all my opamps to LT1001 and it completes with no errors. With the lm324- (National), I get the time stamp error, with the lm324_, it progresses in pico seconds, takes for ever.
I tend to try for perfection in designs, so I downloaded several Lm324s and renamed them lm324_, lm324-, lm324 from TI, Onsemi, Fairchilds, etc. Spice seems like it prefer the LT line of devices.
Does it really matter which model of opamp I use for simulations or can I just use the LT series.
Thanks again for the help,
Kinarfi

 

[ericgibbs]

hi,
The LT1001 according to the datasheet is precision OPA, I would say the problem with the LTS sim, is the LM324 model, I have problems with other projects when using it.

 

[MrAl]

Hi,

I havent looked at these models that closely but spice has a problem with some of the sub circuits because they are not real sub circuits they are very fictional in an attempt to get a simpler model that runs faster. The drawback is that some of the internal sources may generate a fast changing value that makes the derivatives very very high thus forcing the math routine into an overflow or forces the variable time step routine to choose a tiny tiny step just to satisfy some max derivative criterion.

As you noted now one way to get around this is to find a better model, but another way is to simply slow down some of the stiff parts of the circuit. This could be a capacitor with no series resistor for example, and after some real life resistance is added in series suddenly the derivatives behave much better. An inductor with no parallel resistance can cause this too. Sometimes a cap or inductor with added initial value will help, sometimes it will make things worse if an initial value is not close to some particular value.
There are various things to try, most involving slowing down the circuit to some degree, even a tiny amount can do it sometimes without bothering the more significant variables.
Real life (sub) circuits saturate too with large changes which automatically acts as a slowing agent, while spice models dont always limit anything like that. Adding diode clamps here and there could help in that case.

 

[kinarfi]

So with all that being said, not that I know for sure what was said, , would you suggest the use the LT series of components instead of .subs from TI, or ONsemi, or National? Is there a cross reference somewhere? For instance which LT would you use for an LM324 and which LT for a TI TLC2274CN Quad OpAm?
Thanks so much,
Kinarfi

 

[ericgibbs]

So with all that being said, not that I know for sure what was said, , would you suggest the use the LT series of components instead of .subs from TI, or ONsemi, or National? Is there a cross reference somewhere? For instance which LT would you use for an LM324 and which LT for a TI TLC2274CN Quad OpAm?
Thanks so much,
Kinarfi

Hi,
This LT link is the equiv for LM324, its also in the LTSpice lib
https://www.linear.com/product/LT1014

extract;
The LT1014 is the first precision quad operational amplifier which directly upgrades designs in the industry standard 14-pin DIP LM324/LM348/OP-11/4156 pin configuration. It is no longer necessary to compromise specifications, while saving board space and cost, as compared to single operational amplifiers.

 

[MrAl]

Hi,

Yeah and only 5 to 10 dollars each (chuckle) at Digikey. LM324 about 50 cents each.

Any cheaper sources out there?

 

[SgtWook]

Avnet Express has the LT1014DN in stock for $2.73/ea when buying in single quantities.

It's a TI version, so check TI's datasheet on it to make sure it has the same specs.