Line isolation transformer

A line isolation transformer for telephone use is a special type of impedance matching transformer that is used to couple telephone land lines to subscriber equipment to prevent dangerous common mode voltages from appearing on the line. It has a specific 600Ω input impedance which matches the telephone equipment.

A "wet" type will maintain its characteristics while passing the DC current needed to seize the telephone line (signal off-hook to the central office). It is also made with a gapped magnetic core that is not used in normal transformers. A "dry" isolation transformer need not carry DC current and an alternative DC path would be provided. [1]


See also

References

  1. ↑ http://www.randolph-telecom.com/articles/AN-5,%20Transformer-based%20phone%20line%20interfaces%20(DAA,%20FXO),%20Rev1.pdf AN-5 TRANSFORMER-BASED PHONE LINE INTERFACES (DAA, FXO) by Joe Randolph, retrieved 2018 March 20
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