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A simple spice problem...

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GrayFox

New Member
This circuit makes (LTSpice) ill. It is suppose to be a full wave rectifier with a capacitor to smooth out the ripple...It complains about the node to the right of the resistor.

If I remove the capacitor I think it works...

--Jerry
 

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Roff

Well-Known Member
Right click on the diodes and pick a real diode model. I think the problem is the simplified "D" model has no resistance, so the capacitor looks like a short to the voltage source.
 

GrayFox

New Member
Ron H said:
Right click on the diodes and pick a real diode model. I think the problem is the simplified "D" model has no resistance, so the capacitor looks like a short to the voltage source.

Thanks, I will give it a try. I also got it to work by changing gmin from 1e-12 to 1e-11 and using the "gear" integration method.

The circuit provoked a bit of discussion on the LTSpice yahoo group.

--Jerry
 

Nigel Goodwin

Super Moderator
Most Helpful Member
Russlk said:
Every node has to have a path to ground, the diode model is probably open at some point. If you put 10 meg in parallel with the diodes, it will most likely work ok.

Perhaps it's just me? - but I'm doubtful about the usefulness of a simulator if you have to modify circuits for it to work!.

If it can't be trusted to accurately simulate an extremely simple circuit like a bridge rectifier - how can you trust it with more complicated designs?.
 

Roff

Well-Known Member
Nigel Goodwin said:
<snip>If it can't be trusted to accurately simulate an extremely simple circuit like a bridge rectifier - how can you trust it with more complicated designs?.
Spice is both a blessing and a curse. It can lead the inexperienced person down the garden path, or completely confound him (garbage in, garbage out). Speaking of "more complicated designs", we would not be participating in this forum were it not for Spice and other simulators.

I started designing circuits long before Spice was available to me, so I learned how to design without it, and I learned about parasitics and model inaccuracies, etc., and yet I use Spice at work and for fun, because I can "breadboard" circuits in minutes that otherwise would require days (including procuring parts), and therefore might never get done.
 
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