I am build a band pass filter but I am wondering if one of the inductors in my filter can act as a transformer at the same time. I'm assuming not since it would be sending all its magnetic energy into the secondary rather than back into the primary. Can someone confirm this for me please? Also, if it DOESN'T act as an inductor than would it be okay to put it in parallel into my filter? Or do I put it in series? Where do I put it lol?Thanks
The primary of a transformer has a fairly large inductance called the magnetizing inductance. This inductance could be used as a filter, but it is not a good idea. First of all, it will not support any appreciable DC current, because it will saturate. In addition it is usually very nonlinear. If you want to filter the input voltage use a separate filter.
Yes - a transformer is an inductor with a second winding that is coupled to the first via the magnetic field they share. But using the transformer as an inductor will reflect whatever load is on the secondary winding into the primary to diminish the Q and possibly alter the inductance of the primary, and this will affect the bandpass and slope of your filter. Best to get the filter section working right and follow that with a buffer amplifier to isolate it from downstream loading.
A transformer *is* a pair of coupled inductors. A power transformer is designed to have a very high inductance on both sides and a very strong mutual inductance. A linear transformer is not designed to have high inductance, but rather to have a relatively normal value of inductance (milli-henries to micro-henries) and a similar mutual inductance. Linear transformers are often used in mixers. As to your question, usually to get inductors to act as transformers you have to get them close together, usually having the coils either intertwined or line up the cores with each other. Putting the inductors in parallel (that is, no series capacitor between them) won't make them act as a transformer, but it will lower the equivalent inductance: L' 1/(1/L1 + 1/L2)
A Transformer can be both a car and a robot
Transformer primary winding are used as part of a tuned band pass filters in radio and tv intermediate frequency amplifiers while at the same time the complete transformer is being used to couple the intermediate frequency from one stage to the next. But it depends on the application whether are not it is advisable to use a transformers winding as part of a filter while at the same time using the transformer as a coupling device. Any wound wire contains inductance regardless of whether it is part of a transformer or not. At resonant frequency parallel resonant circuits offer maximum opposition to current flow and series resonant circuits offer minimum opposition to current flow. This fact and whatever it is you are trying to accomplish with the filter will determine whether to place the filter in series or in parallel with the signal path.
