Why is communication equipment used - 48V direct current?
In order to simplify the power supply equipment, program-controlled switches, current transmitter and other equipment, are used in -48V power supply. Because program-controlled switches and telephone users in the distance is far, in order to ensure a certain range of services, switching power supply voltage can not be too low, so the communication equipment unified use of -48V power supply. In the PBX equipment, the switch is close to the telephone, and generally uses -24V power, not -48V.
A large number of relays and other components are used in communication equipment, and DC power supply is used. The humidity in the air always exists. In the electrolysis of the direct current, the anode is always subjected to electrolytic corrosion. If the power supply is +48V, the core equipment connected with frame relay, the coil is energized, the coil will be eroded by the line size is very fine, the failure rate is relatively high; the power supply electrode (rack), coil power is negative voltage, the corrosion will be very large volume of iron core, fault the rate will be greatly decreased. Therefore, the communication equipment adopts the positive grounding mode, and uses the negative voltage power supply.
In fact, with a variety of communication power supply: electromechanical switches such as old-fashioned, step-by-step, and standard, are -60V; -24V (carrier indoor electronic tube filament and relay power, power transistor carrier) and +130V (anode power supply).
