AC line Filter design using LT Spice

Thread Starter

visheshseshadri

Joined Jul 17, 2018
5
Hello,

I am fairly new to LT Spice but have done some transient analysis. I have some experience with ADS but I dont have the license due to which I am using LT Spice for my simulation. I am trying to simulate an AC line filter and calculating attenuation. The following are the specifications:
Impedance :
AC output to ground at 400kHz : 5.7-j725 ohm
AC output to ground at 800kHz : 34.2 +j33 ohm
210V AC line to line
210V AC line to ground
25A rms AC
Red and Black are used for input 1 and 2

I have attached my half done model and the circuit with specs. Please let me know how to use the variable impedance function and the bode plot feature.

Thanks.
 

Attachments

crutschow

Joined Mar 14, 2008
24,967
You need to add the load at the output to get the attenuation.

The .ac analysis you are using generates a Bode plot.
Just click on the output after the simulation.

What's a "variable impedance function" and why do you think you need it?
 

Thread Starter

visheshseshadri

Joined Jul 17, 2018
5
You need to add the load at the output to get the attenuation.

The .ac analysis you are using generates a Bode plot.
Just click on the output after the simulation.

What's a "variable impedance function" and why do you think you need it?

Thanks for the quick answer. It worked. The filter output (load) goes into a system which also has an RF input. The system impedance varies. This filter prevents RF from entering the AC mains. I now have another question. I realize that the spice command .ac oct 101 100k 15M should give the x axis as 101 points per incrementing octave from 100kHz to 15 MHz. But the plot ends at 100kHz. Appreciate some help regarding this. Please see the attachment. Thanks.
 

Attachments

crutschow

Joined Mar 14, 2008
24,967
I realize that the spice command .ac oct 101 100k 15M should give the x axis as 101 points per incrementing octave from 100kHz to 15 MHz.
Nope.
Spice is insensitive to letter case so M is interpreted as m (milli).
For MHz you need to use Meg.
And try using more increments, such as 1k.

See attached:

1591116532116.png
 
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