still a newbie - another getting started with LT SPICE problem

[dave]

Still having a problem understanding this aspect of LT Spice.

Say I draft a circuit. I must put a (voltage) source in - say sine at
a constant frequency

eg SINE 0 10 150.

If I then want to see what happens to that circuit across a range of
frequencies I must insert a .ac command, which allows me to specify a
start and stop frequency.

eg: .ac lin 50 100 1000

when I do this I get an error saying

No AC stimulus found:
Set the value of a current or voltage source to "AC 1."
to make it behave as a signal generator for AC analysis.


I'm clearly not understanding dot commands (and probably lots of other
things) - but I thought I *had* set an AC stimulus with the SINE
"generator device" (A circle with a + - in it and the word SINE and
<args> along side it. I also thought (perhaps) the frequency arg in
the sine command would be replaced by the frequence sweep in the .ac
command - but it seems it completlely separate.

Please… explain what I should do to do this correctly.
Thanks

 

[Andrew Holme]

Still having a problem understanding this aspect of LT Spice.

Say I draft a circuit. I must put a (voltage) source in - say sine at
a constant frequency

eg SINE 0 10 150.

If I then want to see what happens to that circuit across a range of
frequencies I must insert a .ac command, which allows me to specify a
start and stop frequency.

eg: .ac lin 50 100 1000

when I do this I get an error saying

No AC stimulus found:
Set the value of a current or voltage source to "AC 1."
to make it behave as a signal generator for AC analysis.


I'm clearly not understanding dot commands (and probably lots of other
things) - but I thought I *had* set an AC stimulus with the SINE
"generator device" (A circle with a + - in it and the word SINE and
<args> along side it. I also thought (perhaps) the frequency arg in
the sine command would be replaced by the frequence sweep in the .ac
command - but it seems it completlely separate.

Please. explain what I should do to do this correctly.
Thanks

In the properties dialog of the voltage source, you had the SINE function
radio button selected. Change this to NONE. The small signal AC analysis
fields on the right-hand side will then be enabled. Enter 1 in the AC
amplitude field and click OK.

 

[dave]

In the properties dialog of the voltage source, you had the SINE function
radio button selected. Change this to NONE. The small signal AC analysis
fields on the right-hand side will then be enabled. Enter 1 in the AC
amplitude field and click OK.

Ah I see. Thanks.