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skidave 8th August 2012 01:19 AM

Sine Wave Question
 
I just downloaded the latest version of LTspice and I am having an issue with generating a sine wave for a power supply I am simulating. I need to simulate a power transformer with 360 volt secondaries (for a tube amp). I'm missing something when I select a voltage source and set it for sine. The sine wave form is going from 0 to 360 (bottom half peak is at 0 and top is at 360). Why is it not showing the 0 reference in the middle of the waveform and displaying the negative half of the cycle in the negative numbers. I don't remember this in the earlier version I was using.

Am I missing something?

Thanks in advance.

RJM1 8th August 2012 06:33 PM

1 Attachment(s)
Do you mean something like this?

tvrgeek 8th August 2012 10:07 PM

Voltage source setup tab, offset.

skidave 9th August 2012 01:26 AM

1 Attachment(s)
Thanks for the replies. See attached and what is happening.

Where is the voltage source setup tab; is this the right click on the component to set the voltage?

I can't believe I'm missing this!

Attachment 295255

Elvee 9th August 2012 01:27 PM

1 Attachment(s)
Quote:

Originally Posted by skidave (Post 3119782)
Thanks for the replies. See attached and what is happening.

Where is the voltage source setup tab; is this the right click on the component to set the voltage?

I can't believe I'm missing this!

Attachment 295255

Everything is OK, but your source is floating, and to see its voltage you must measure across it, not with respect to ground.
That's the same in real life anyway.

To measure across something, the easiest way is to left-click on what you consider as the "hot" node, and keeping the button depressed move to the cold node. This will give you something like Nxyz,Nabc.
You can also enter that expression manually in the trace name:

skidave 9th August 2012 05:17 PM

Thanks Elvee! I just tried it and it works. Makes sense now because it is not ground referenced. As well, I did not know how to measure across a component...I do now.

On another note, I have noticed another circuit is not showing the RC time constant when you simulate it. Do I have to change something in the simulate command to show the cap charging? It just simulates with the cap at full voltage. I don't remember having this issue in version III.

macboy 9th August 2012 05:31 PM

By default, LTSpice will determine the DC (steady state) operating point and simulate from there. If you want your power supplies to start with 0 volts, there is a checkbox for that in the edit simulation command window. You can also choose to skip the initial operating point solution.

skidave 9th August 2012 06:01 PM

Thanks Macboy. I did find that and now it simulates properly.

Thanks everyone!

Dave


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