MOBILE COMPUTER AND THE EXTENSION SYSTEM WITH TELEPHONE LINE SELECTING CONTROL FUNCTION

摘要

PURPOSE: A portable computer having a telephone line selection control function and an extension system of the same are provided to selectively connect with a telephone line through a portable computer or an extension system and decrease the level of a telephone line signal between the extension system and a computer even when connected with a telephone line through an extension system. CONSTITUTION: A telephone line is selectively connected with a telephone line connector(130). A transformer(122) increases a signal transferred from a computer to a remote place to 50V and decreases the signal from the remote place to 5V. The ratio between the winding(n1) of the primary coil of the transformer(T1) of the transformer(122) and the winding(n2) of the secondary coil is 1:10. A static current DC holding circuit(230) and a protection circuit(362) are connected in parallel between both ends of the telephone line connector(130) and the secondary coil of the transformer(T1). A static current DC holding circuit(215) and the protection circuit(252) are connected between the telephone line connector(230) of the extension system(200) and the secondary coil of the transformer(T2). The relay unit(123) is formed of two switches(sw1 and sw2) and a coil(L1).