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how to use transformers as a lowpass/bandpass filter?

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jlee

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Can someone explain how to use transformers as lowpass filter or bandpass filter? I want to build a low-pass/bandpass filter which is at least 3rd oder. Can you please refer some good reference?

Thank you very much!
 

Hi jlee,
Usually filters are not built using tranformers.
Commonly used filters are
1. Passive RC, RL ,RLC filters
2.Active filters (RLC)
3. Switched capacitor filter.
4. Digital filter.

If the application is known then appropriate suggestion can be given

Not getting why an transformer has to be used for filtering.
regards,
sudhir
 

Actually transformers are being used to synthesize filters. The design is based on LC ladder filter. In some cases, the inductors in LC bandpass filter are impractically big. In such case, we need to transform the too big inductors into transformers. I found the following helpful document on the web, which briefs how to do the "Norton transform" to size down the too big inductor in LC bandpass filter:

**broken link removed**

If anyone knows more about how to use transformers in LC filters, please point me more reference. Thank you very much.
 

I was reading the document about Norton transforms... I still don't understand the following two transforms. Attached the transforms details in .jpg format. Can anyone please provide the mathematical proofs on the two transforms (inductor transform and capacitor transform)? Thank you very much
 

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