In communication, we often find that most of the communication power supplies are powered by -48V. In fact, there are many reasons and considerations for such a standard. Here we will discuss in depth why most of the communication power supply -48V power supply, and a series of related issues.

1.The classification of utility power
In understanding why the communication power supply is -48V, we first recognize the classification of utility power. Utility power, that is, the alternating current used in our daily life, is generally divided into the following categories:
Single-phase power: consists of one fire wire and one zero wire, and the voltage is usually 220 V. It is mainly used in households and small commercial places.
Three-phase power: composed of three fire wires and one zero wire, and the voltage is usually 380 V. It is widely used in industries, large commercial places, etc.
As one of the input sources of communication power supply, utility power needs to go through a series of conversion and processing in order to provide stable and reliable DC power for communication equipment.
 
2.-48V power supply is how to generate?
In general, the generation of the -48V power supply can be described in the following process: Utility input: First of all, utility is inputted into the communication power system. Utility can be 220V or 380V AC. Rectification: The AC should be converted to DC by a rectifier. Rectifiers use diodes and other electronic components, convert the positive and negative half of AC into the same direction of DC.
Filtering: the ripples and impurities are filtered out from the rectified DC so that the DC becomes smoother and more stable. Voltage Stabilization: stabilize the DC voltage at -48V through the voltage stabilizer circuit, which can automatically adjust the output voltage according to the changes of the load to ensure the communication equipment always get a stable power supply. After going through the above steps, one can generate the -48V communication power supply.
 
3.Why -48V power supply? Instead of +48V
Communication power supply -48V power supply instead of +48V, mainly for the following reasons:
Historical reasons
In the early communications systems, electronic tubes and other equipment require a higher voltage to work. In order to ensure the stability and reliability of the equipment, -48V was chosen as the standard voltage for communication power supplies. This standard was carried over as communication technology continued to develop.
Early equipment like telephone exchanges used electromagnetic relays, which require a large change in current when they are engaged and disengosed. The use of -48V power supply enables the relays to have relatively small current variations when they are engaged and disengosed, thus improving the reliability and stability of the equipment.
Safety Factors
The safe voltage for the human body is usually considered to be 36V or less. With a -48V supply, in the case of ground fault, etc., the current flows to earth through the grounding resistor without direct shock hazard to the human body. With a +48V supply, in the case of ground fault, current will flow from the body to earth, increasing the risk of electric shock.
-48V power systems are often designed with grounding protection to further enhance system safety. When a ground fault occurs in the system, the grounding protection device will quickly cut off the power supply and prevent the accident from expanding.
Technical Factors
In communication systems, many electronic devices use semiconductor devices such as diodes, transistors, and integrated circuits. These semiconductor devices require stable power supply voltage for their operation and are very demanding in terms of the ripple and noise requirements from the power supply. The use of -48V power supply can provide semiconductor devices with a more stable and cleaner power supply by using techniques such as the voltage regulator circuit and filter circuit so that it improves the performance and reliability of the equipment.
Compared with the transmission and distribution of power, the -48V power supply system has smaller line losses and voltage drops. This is because when the power is the same, the smaller the voltage, the larger the current, and the line loss is proportional to the square of the current. Thus, the application of -48V power supply can reduce the line loss and raise the effectiveness of power transmission.
 
4.What is the difference between -48V and +48V?
There are several differences between -48V and +48V:
Different polarity
This is the most obvious difference. -48V means that the negative pole of the power supply is -48V relative to the ground, while +48V means that the positive pole of the power supply is +48V relative to the ground.
Safety Differences
As said before, the -48V has an edge over its counterpart in the perspective of safety since upon a ground fault occurrence, the current will flow through the grounding resistor to earth without causing direct shock to the human body. Whereas, on the other hand, in case of a ground fault in +48V, current will find its path to earth via the human body and thereby enhance the probability of getting electric shock.
Technical characteristics
In the design of communication systems, there are devices that may require specific polarities in their power supplies. For instance, some semiconductor devices operate only under certain polarities. Thus, it is during the designing of a communication system that one has to choose between the polarities of power supplies about the requirement of the device.
Also, technical requirements for voltage regulation, filtering, and grounding protection of the power supply systems may be different for -48V and +48V, among other.
 
5.Which countries have adopted the -48V power supply system?
Although the -48V power supply system is widely used in the communication field, not all regions of the world adopt the -48V power supply. Different countries and regions may choose different communication power standards according to their own actual situation and needs.
In some European countries, for example, a -60V or other voltage level power supply system might be adopted. While in developing countries where power infrastructure is relatively weak, it's not that rare to adopt flexible power, such as solar and wind energies.
However, with the globalization of communication technology, more and more countries and regions are implementing international standard communication power systems to enhance the compatibility and interoperability of communication equipment.
 
Most of the communication power supplies adopt -48V power supply is determined by the historical reasons and safety factor and technical factors and so on. The generation of -48V power supply has gone through utility input, rectification, filtering, and voltage stabilization. Compared with +48V, -48V has some superiority in safety performance and technical features. Although not all regions in the world have adopted -48V power supply systems, with the development of communication technology, international standard communication power supply systems will be widely used.
In the future communication field, with the continuous development and innovation of technology, the communication power system will continue to develop and improve. We can expect more efficient, safe, and reliable communication power solutions to emerge, which can strongly support the continuous development of the communication industry.Why does most of the communication power supply use -48V power supply?