Need help modeling IF transformer in LTspice

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Tsif said:
Pardon c'est la première fois que je vais utiliser les transformateurs FI. Est-ce que je peut inverser le primaire et le secondaire lors que j'utilise le transformateur? et encore merci à ronsimpson pour ses explication.
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Sorry for the first time that I will use the transformers FI. Can I reverse primary and secondary when I use the transformer? And again thanks to ronsimpson for his explanation.
Click to expand...
You can reverse the transformer.
 
alec_t said:
Intuitively I still think the inductance sum of the two primary sections (i.e. from pin 1 to 3) should be 680uH,
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Intuitively, never stated.
alec_t said:
268uH and 412uH respectively. Correct me if I'm wrong.
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Back in post #13 I have the two windings at 208uH and 135uH which is 1.54 like you say. I agree in the ratio but not on the value. The values do not add up to 680uH
 
alec_t said:
(Anglais, s'il vous plait).
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forgive me it's an habit.

alec_t said:
Depending on your circuit, reversing the primary and secondary could still work,
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thanks alec_t.

I prefer to re-write this post here:

Sorry it's the first time that I will use the IF transformers. Can I reverse primary and secondary when I use the transformer? And again thanks to ronsimpson for his explanation.
 
Something that may have been overlooked is that the coupling coefficient in an IF transformer is considerable less than one, and I don't think anyone mentioned that. (I read through all the posts rather quickly so I may have missed it.) That will affect the inductance seen on one side of the transformer due to the inductance on the other side.
 
Hi every one,

I don't know if I must create a new post for this question because there is still a link with this title and I will write it here.
This is my problem:



I want to have 2.5V peak to peak at the output of the transformer (on point C). On point A I have 3.3V and on point B I have a signal 120mV an in the output I have 12mV. I think reverse the primary and secondary is the solution but it isn't. Please I need a help. Thanks
 
Last edited:
Tsif said:
on point B I have a signal 120mV an in the output I have 12mV.
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Looking at the turns ratio, I would expect those voltages.

Tsif said:
I think reverse the primary and secondary is the solution but it isn't. Please I need a help.
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Can I suggest that you tell us what it is that you are trying to do.
Just tell what you want to do, not how you incorrectly think the problem should be solved.

Going around in circles trying to make some bad idea work the way that you think it should, is usually a waste of time.

JimB
 
JimB said:
Can I suggest that you tell us what it is that you are trying to do.
Just tell what you want to do, not how you incorrectly think the problem should be solved.
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Thanks for your answer JimB. So I want to creat an transmitter PLC, I want to use 455KHz as frequence; And I want to creat an coupling circuit with IF transformer.
 
To talk on the power line you need to reduce the 50/60hz signal, and 100/120hz noise.
Your 455khz signal might be 0.1 volt while the power line is 220V or 110V.
I added a high pass filter (R3, C3) that will reduce the power line frequency.

 

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Sorry for the answer very late, because I was in the countryside, and I haven't internet.
Thanks ronsimpson.

I want to use the IF transformer for galvanic isolation for the transmitter and I don't know how to branch it. For the receveir I think it's OK. And for all the circuit that you suggest to me what kind of transformer are the circuit used? thanks a lot.
 
Tsif said:
I want to use the IF transformer for galvanic isolation for the transmitter
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Are you sure the transformer insulation and coil separation are rated for line voltage? IF transformers are normally used at low voltages only.
 
alec_t said:
Are you sure the transformer insulation and coil separation are rated for line voltage? IF transformers are normally used at low voltages only.
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thanks alec_t; yes I know IF transformer is for low voltage; Or if I can eliminate the 50Hz (220V/50Hz) I can use IF transformer. I thik I can use an RC high pass filter to incrase the 220V .
 
ronsimpson said:
Look at some of the schematics I provided. Some use two small high voltage capacitors to isolate from the power line.
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Thanks ronsimpson. do you know what kind of transformer I can use if I want to replace the IF transformer? is an smps transformer an solution? and where I can find an smps transformer? thanks a lot.
 
Here is a "pulse" transformer. Primary to Secondary voltage can be as high as 1500 volts.
330uH but not adjustable like the IF transformer. So you will have to put a capacitor across it. Then maybe adjust the cap a little to get the frequency right.

Look at pulse transformer; Usually 1:1 turn ratio but some are different. Look at the insulation voltage.
I found this one at digikey.com but most parts supplies will have them.
 

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