Hi:

Can someone please tell me why the secondary voltage on the transformer
is not a sine wave?

Thanks,

M

 

Can someone please tell me why the secondary voltage on the transformer
is not a sine wave?

Are you sure?

 

I think you are measuring Vsec to ground which looks bad.
Hold the mouse over Vsec1, mouse down, do not release, move the mouse to Vsec2 and release.

 

I added a 2nd net name to the secondary and measured the voltage across the secondary. It looks like a pretty good sine wave. Sorry I misread the original post. As a side note it is not required to put a GROUND symbol on the primary side.

 

I think you are measuring Vsec to ground which looks bad.
Hold the mouse over Vsec1, mouse down, do not release, move the mouse to Vsec2 and release.

Your LTSpice technique is better than mine. I would have put together an equation of one minus the other (a bit more work). Can you point us to something more detailed? I find many things in LTSpice to be counter-intuitive...a comma?

 

As a side note it is not required to put a GROUND symbol on the primary side.

I though LTspice does not like floating nodes (?).

 

I thought LTspice does not like floating nodes (?)

As long as there's at least one ground symbol on the schematic it seems happy. In the present case the primary-side ground symbol can be removed. Presumably the coupling between the coils is an adequate reference? The lower node of V1 is 0V here, relative to the remaining ground node..

 

As a side note it is not required to put a GROUND symbol on the primary side.

Older versions of LTspice needed a ground on the primary side. I just upgraded SPICE and it is OK with floating nodes.

 

hi maker,
Try this option va,vb and Common Press F4 key
E

 

Older versions of LTspice needed a ground on the primary side. I just upgraded SPICE and it is OK with floating nodes.

Perhaps it now adds a large default resistance from any node to ground to prevent a calculation error.

 

Perhaps it now adds a large default resistance from any node to ground to prevent a calculation error.

Perhaps they rewrote the code to allow isolation transformers.

 

Older versions of LTspice needed a ground on the primary side. I just upgraded SPICE and it is OK with floating nodes.

I don't have a working copy of LTspiceIV so I can't confirm your assertion. It works fine without the GROIND on the primary side in LTspiceXVII. Excuse me fer livin, but your claim seems dubious without more details. Your previous version must have been more than 7 years old.

 

It works fine without the GROIND

I have never had one with Groind.

I just upgraded SPICE and it is OK with floating nodes.

What about noating flodes?
Sorry it is Sunday, I just enjoyed a great Pale Ale, and I am making a bit of trouble. :-(

Seriously the REAL transformer ought to have at least some capacitance across the isolation barrier, but that still does not help establish a DC reference point. I think that LTSpice needs some sort of reference in order to tell you what is the voltage between some point on the primary and ground. But different transformers will behave very differently. I assume that a simple transformer is considered to be relatively ideal in LTSpice.