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Re: Specifiying multiple grounds in LTspice

 

Jerry,

This is not a SPICE or LTspice limitation.? If you had to solve a circuit with a bunch of nodes isolated from ground and wanted to solve the voltages at all the nodes, you couldn't do it, because the?voltages at the floating nodes are undefined.? LTspice can't do it either.

Rick
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On Sunday, December 8, 2013 10:12 AM, Jerry Lee Marcel wrote:
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Le 08/12/2013 14:07, Andy a ¨¦crit?:
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The only LTspice requirement, is that every circuit node must have a DC path to GND ...

Some people don't seem to like that, if they have a circuit with an isolation transformer that keeps a part of their circuit actually isolated from the GND that appears elsewhere in their circuit.?
I believe the reason is when a transformer is properly modelled with its stray capacitances, the results will be different in function of the way the floating part is made non-floating.
Particularly there will be a big difference with one leg of the output directly connected to ground compared to having both legs connected via 1Meg resistors.

This limitation of LTspice is not a problem for me, since it is part of my routine to evaluate transformers with all sorts of connections, unbalaned in particular.
I must admit this limitation may be a hindrance for users who are not comfortable with transformers intricacies.


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