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Lundahl LL1545A LTSpice Simulation Issues
Lundahl LL1545A LTSpice Simulation Issues
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Old 2nd November 2017, 02:04 PM   #1
lemon is offline lemon  Greece
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Default Lundahl LL1545A LTSpice Simulation Issues

Transformer LTSpice simulation issue.

I tried to LTSpice simulate a Lundahl LL1545A transformer to the AK4490 differential dac output, but I have FR simulation issue.
I have done an internet search about how is the right transformer LTSpice setup but the information are less.

For example, see for the Lundahl LL1545A the right LTSpice setup will be like 2 primaries coils and 4 secondaries coils with K L1 L2 L3 L4 L5 L6 0.999 spice directive.

I have done the following schematics.

shematics.jpg

If you done a real FR measurement with 20K load on the above setup by Spectrum Analyser or oscilloscope or rms multimeter, you will see that FR output is flat btw 20-15KHz, with a small increase voltage btw 17K-50K and then there is significant decrease until cut-off.

The best FR output that I have with LTSpice is the following, that is wrong.

FR.jpg

The LTSpice have a dialogue window for Coil setup like this.

LTSpice Coil Setup.jpg

But for the example, if you measure each primary coil by DER EE DE-5000 you have the following table.

LL1545A primaries.jpg

How is the right setup on LTSpice, can someone help?
I have included and the LTSpice .asc file
Attached Files
File Type: asc AK lundahl Super VI Simulation.asc (3.9 KB, 6 views)
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Old 2nd November 2017, 03:00 PM   #2
abraxalito is offline abraxalito  United Kingdom
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A couple of issues you have - firstly the series resistance of the windings needs to come from Lundahl's own data (305R for primaries, 122R and 182R for secondaries). Sorting this out fixes up the frequency response very nicely (I zeroed your shunt resistance and capacitance though to get clear what's happening initially). With the correct series R I get -1dB at almost 400kHz.

Second the inductances of a transformer depend on the frequency (and to some extent the amplitude used to measure with). The turns ratio comes out of the ratio of inductances so its best to tweak the secondary inductance to be in line with what the turns ratio is.
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Old 2nd November 2017, 03:30 PM   #3
pieter t is offline pieter t  Netherlands
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Quote:
Originally Posted by abraxalito View Post
The turns ratio comes out of the ratio of inductances so its best to tweak the secondary inductance to be in line with what the turns ratio is.
Take care: with for example 1:2 turn ratio the inductance ratio is 1:4.
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Old 2nd November 2017, 04:36 PM   #4
pieter t is offline pieter t  Netherlands
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6k7 resistor and 470 pF capacitor should be in series; sim is wrong.
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Old 2nd November 2017, 04:39 PM   #5
lemon is offline lemon  Greece
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@ abraxalito = From Lundahl's datasheet the 305R for primaries, 122R and 182R for secondaries, are described like static resistance and not series resistance.
Probably it is the same, but I confused with the Rs (Series Resistance) and Rp (Parallele Resistance) of De-ee measurings.

@ pieter t = like 5H on primaries inductance and 20H at the secondaries (in series)?

Abraxalito, can you attach me the file that you described like -1dB at 400K?
Here a new .asc file with the Lundhal's datasheet values.

Thanks for the help guys!
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Old 2nd November 2017, 04:43 PM   #6
lemon is offline lemon  Greece
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Quote:
Originally Posted by pieter t View Post
6k7 resistor and 470 pF capacitor should be in series; sim is wrong.
The datasheet says "Frequency response (source 600 Ohm, load (6.7 k + 470 pF) in parallel with 56 k ).
I think that it means in series the 6K7+470p and all of this parallel to the output.
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Old 2nd November 2017, 04:45 PM   #7
pieter t is offline pieter t  Netherlands
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When I am right you use the transformer with 1:1 ratio (2+2:1+1+1+1).
Then you must have equal inductance for the primary and secondary.
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Old 2nd November 2017, 04:47 PM   #8
pieter t is offline pieter t  Netherlands
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Quote:
Originally Posted by lemon View Post
The datasheet says "Frequency response (source 600 Ohm, load (6.7 k + 470 pF) in parallel with 56 k ).
I think that it means in series the 6K7+470p and all of this parallel to the output.
Right, but that's not what you did in the sim.
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Old 2nd November 2017, 05:27 PM   #9
lemon is offline lemon  Greece
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Oops, it is clear to me now!!
pieter t you had right, my sim is wrong, I have the R//C at the output.
Now, it is very close to the real measurement.

I have used the Series Inductance that I have measured with De-ee at 1KHz, 8.3H in primaries and 2H at primaries.
With the inductance ratio 1:4 (Prim. to Sec. ratio 1:2) which is the right?
Attached Images
File Type: jpg FR.jpg (206.8 KB, 74 views)
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Old 2nd November 2017, 06:02 PM   #10
lemon is offline lemon  Greece
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Quote:
Originally Posted by lemon View Post
...
I have used the Series Inductance that I have measured with De-ee at 1KHz, 8.3H in primaries and 2H at primaries.
With the inductance ratio 1:4 (Prim. to Sec. ratio 1:2) which is the right?
Wrong typo...I meant "I have used the Series Inductance that I have measured with De-ee at 1KHz, 8.3H in each primary and 2H at each secondary.
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