Coil alternative (maybe semiconductor based design) ?

Question

Hi :)I am trying to build some kind of telephone interface.My circuit should act as telephone central, so it must give power supply to connected phone. Also 2wire/4wire decoding is needed. I found suitable schematics - you can see it there: But in this circuit there are two coils (L2 L3)  which separates direct current from signal, 210 mH each (to big size for me). I am searching for any solution to replace this coils with something else.Is it possible?Maybe some kind of 'dummy inductance' or current source realized with opamp driwing power transistor?Thanks for any help.For those who dont want to download PDF from link given above there is schematics of interested part of circuit.    - 50V       |       |      L2       |                   +-----------C----        |       oTo phone                       rest        o                    of        |                    circuit       +-----------C----       |      L3       |       |     -----      ---       -

Luhan · Accepted Answer

Here is my 2 phone tester.  Maybe some of this is useful to you - noinductors.  One phone rings, the other just connects DTMF and audio...Luhan

Roger Hamlett · Answer

Do a search for 'gyrator'. This is a circuit, that allows a couple of op-amps, and a capacitor to simulate the behaviour of an inductor. This is used in all current modem interfaces. Before this, the line interface chokes were _huge_.

Best Wishes

Marcin Szczepaniak · Answer

Dnia 24.12.2006 Roger Hamlett  napisa³/a:thanks, this is _exactly_ what i need ! :)

Ross Herbert · Answer

In old electromechanical exchanges the battery feed arrangement in the line circuit was performed by a dual coil relay of 200 + 200 ohms with a magnetic core of soft iron with 3 nickel-iron sleeves and bakelite front cheek to provide low dc resistance and high impedance to voice frequencies. This was not a huge relay either.

If you can find a 2nd hand line simulator such as that shown here

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then you won't have to design your own unit.

joseph2k · Answer

I saw it, the patent should not have been granted; prior art.--  JosephKK Gegen dummheit kampfen die Gotter Selbst, vergebens.    --Schiller

Coil alternative (maybe semiconductor based design) ?

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