Why is the power supply negative voltage 48V?
The equipment is normally expected to work within 20% of the voltage fluctuation range. Yes, the -48V system device isThe working voltage range is -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. This means that the collection is required to work 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, as well as someSome countries use -24V's power system. If the product is to be sold in these areas, take care of theseSame standard.
As for the enclosure of the equipment, grounding (PGND), this is for the purpose of protecting the equipmentThe accumulated charge rapidly falls to the ground without damaging the equipment and personnel.Our products basically use the -48V power supply system, and the actual voltage is usually measured- 53.5V. This is because, for reliability reasons, communication devices are equipped with -48vTo ensure the reliable charge of the battery, the supply voltage needs to be slightly higher than the battery voltage.
The positive grounding can reduce the communication signal interference, harmonics and other unfavorable factors
The use of -48V power is a historical cause. Use the earliest passThe telephone network is the telephone network, and the telephone is supplied by the telecommunication bureau. The 48V is chosen as much as possible under the conditions at that timeHigh user to end office distance (36V is safe voltage, more than too insecure). Later for compatibilityEarly equipment, cost reduction considerations, -48V communications equipment or power supply.
Negative power supply system, positive grounding is only used. There's a saying "air"There are a lot of negative charges in the air. According to the electrochemical knowledge, the positive grounding can adsorb negative ions in the air,Thus, the casing of the telecommunication equipment is protected from corrosion. In fact, this statement is not quite right. Galvanic cell reaction andElectrolytic reactions can lead to rusting of equipment, but because they exist in micro form on the equipment,Almost no effect. For example, the network of non communication systems is negative grounded (for example, the one you are using)But it's not rusty. And the -48V is internally isolated via DC/DC, and DC/DC is lostOut of the negative grounding, nor see the corrosion of single board corrosion. So no matter which pole is grounded, it isSame。
