After looking at this catalog page, I'm a bit confused. What is "IDC Bias" on the telephone coupling transformers and how important is that characteristic in my selection of a transformer???

What is this current for? What does it do?

 

A transformer connected to a telephone line draws DC current. If the current is higher than the amount of current that saturates the transformer then the transformer will not work.
If the central office is nearby then the current will be as high as 90mA.

The current is how the central office senses that your telephone is off hook then it is drawing current. The current causes a ringing line to be answered or causes a dial tone.

 

Thanks. Ok, so i guess the only reason why i need to look at this parameter is to avoid a situation that might cause saturation, aye? I find that a 3.9K in series with the telephone line is usually sufficient to prevent the transformer primary from drawing too much current, yet low enough resistance to make it come online.