Traditional Culture Encyclopedia - Traditional stories - Why do communication devices use -48V DC?

Why do communication devices use -48V DC?

In fact, many kinds of communication power sources have been used: the old electromechanical switches, such as stepping system and vertical and horizontal system, are all-60 V; The carrier chamber electron tube requires -24V (filament and relay power supply, transistor carrier power supply) and+130V (anode power supply). I"W'z o l4t6j\x0d\ Communication equipment uses a large number of relays and other components, and adopts DC power supply. The moisture in the air always exists, and the anode has been corroded by electrolysis under the action of direct current. If the working power supply is +48V, the iron core of relay and other equipment is connected to the frame, and the coil is energized, the coil with fine wire diameter will be corroded and the failure rate will be higher; If the positive pole of the power supply is grounded (frame), and the working power supply of the coil is negative voltage, the large iron core will be corroded and the failure rate will be greatly reduced. Therefore, all communication equipment adopts positive grounding mode and uses negative voltage power supply. ! D/A SB M u 'z u (I \ x0d \ In order to simplify the power supply equipment, the current program-controlled switches, optical terminals and other equipment all use -48V power supply. Because the program-controlled exchange and telephone are far away from users, in order to ensure a certain service range, the power supply voltage of the exchange should not be too low, so the communication equipment uses -48V power supply uniformly. In PBX equipment, the distance between the switch and the telephone is very close, and generally -24V power supply is used instead of -48V. 1r7K? The technical level of Q9\x0d\ telephone is gradually developing, from manual magneto telephone to * * * electric telephone to program-controlled telephone. \ x0d \ x0d \ In the process of development, different kinds of technologies have a transitional stage and a compatible process. For example, after the appearance of color TV, black and white TV can also watch programs with color signals, so the development of color TV technology can not completely abandon the broad audience of black and white TV. The black-and-white signal in color TV technology is similar to the original black-and-white TV. The power supply voltage of \ x0d \ \ x0d \ * * power telephone is 48V, so when developing program-controlled telephone, this voltage level is also adopted to achieve compatibility with * * * power telephone, which will not affect the development of new technology. \x0d\\x0d\ If more advanced wired telephones appear in the future, it is estimated that 48 volts will still be used. \x0d\ In addition, it can prevent electrochemical corrosion; Lightning protection; Strengthen shielding and other functions.