Why does communication equipment use a negative power supply system like -48V?
Through the media may also be aware of the use of -24V power system equipment, which is modern for some of the internal equipment for the design of the use of convenience. Generally measured to the power output voltage 26.8V.The equipment is normally expected to work within 20% of the voltage fluctuation range. For -48V systems, the device requires a working voltage range of -38.4V~57.6V, but we actually require the operating range in general - 36V~-72V. The main consideration is that the -48V system device is compatible - the 60V power system, which requires - 48~-72V. In this way, the collection is called the working voltage range of about -36V~-72V.By the way, the -48V power supply system is only the standard for communication power used in most countries and in china,Not all countries use this standard, for example, Russia will use the -60V power system, and some countries use the -24V power system. If the product is to be sold in these areas, these different standards should be taken into account.The standard of city electricity is also different in the world. For example, China and Europe adopt 220V city electricity system, the United States, Japan and so on are 110V city electricity.
As for the enclosure of the equipment, grounding (PGND), this is for the purpose of protection. The accumulated charge on the equipment is rapidly discharged to the ground without damaging the equipment and personnel.Our products basically use the -48V power system, and the actual voltage measured is - 53.5V. This is because, for reliability reasons, the communication devices are equipped with an alternate battery (-48v), and the supply voltage needs to be slightly higher than the battery voltage in order to ensure the reliable charge of the battery.
Let's begin with the 2 question. The use of -48V power is a historical cause. The earliest communication network used was the telephone network, which was powered by the telecommunications office. The 48V was chosen as far as possible to improve the user's end-to-end distance (36V is a safe voltage, more than too insecure). Later, in order to be compatible with early equipment and cost reduction, the local communications equipment was powered by -48V.
Negative power supply system, positive grounding is only used. The original saying is that there are a lot of negative charges in the air. According to the knowledge of electrochemistry, the positive grounding can adsorb negative ions in the air, thus protecting the shell of the telecommunication equipment from being corroded. In fact, this statement is not quite right. Galvanic reactions and electrolytic reactions can cause equipment to rust, but because they are microscopic in the equipment, they have little impact. For example, the network of non communication systems is negative grounded (for example, the computer you are using), but it is not rusty. And -48V internal isolation through the DC/DC, DC/DC output is negative ground, nor see single board corrosion rust. So no matter which pole is grounded, it is the same.
