The importance of voltage regulators and UPS power supplies to medical devices

Historically, communications industry equipment has been powered by -48V DC. -48V is also the positive ground.
If Baidu searches for this topic, there will always be a "conventional custom" or "a large amount of negative charge in the air. According to electrochemical knowledge, the positive ground can absorb negative ions in the air, thus protecting the outer casing of the telecommunication equipment from being rusted." Quite vague. I graduated from communication major. Although chemistry is taught by physical education teachers, I still can't help but talk about this counter-intuitive (negative power) setting reason, not necessarily rigorous, welcome to make a brick.

In the telephone era, the -48V power supply was applied to the central office to feed the fixed telephone. Suppose the telephone office gathers the point to the user's link, the world is full of water, the water vapor is diffused, and the various terminations and the cable itself are poorly insulated. This is a very common situation, such as being located in some wet pipe or manhole. The voltage of 48V is sufficient for electrolysis of water. The electrolysis process is the oxygen evolution of the positive electrode and the hydrogen evolution of the negative electrode. The oxidation reaction of the positive metal material is quite serious. Due to the existence of the grounding, assuming that the negative electrode is grounded, the negative electrode and the earth have no potential, and the positive electrode exhibits a potential of +48 V, and the positive electrode is rapidly oxidized after oxygen evolution. On the contrary, the positive electrode is grounded, the positive electrode and the earth have no potential difference, and the negative electrode is hydrolyzed to hydrogen. As for the return path of the leakage current, the earth or positive cable can be taken, depending on the magnitude of the reflow impedance. In short, the positive grounding corrodes the metal conductors such as cables much less than the negative grounding. The use of a negative power system for communication power supplies seems to make sense.
By the way, why use 48V voltage? Generally, the voltage is high, it is not safe enough, the cable insulation level is high, and the wet environment is prone to breakdown. The voltage is low and the current is large, which is not suitable. In addition, considering the uninterruptible power supply system using a lead-acid battery, 48V is exactly 12 2V battery cells, and for a small-capacity system, only 12 are used for 12V batteries. A reasonable battery pack with a reasonable number of strings is easy to balance. In short, it is the result of consideration by all parties.
In the -48V power supply system, the AC mains is low-equipped, and the switching power supply is used to convert to DC 54.5-55V to float the battery and output power to the device. easy to understand.
About the voltage of about 54V, mainly by the lead-acid battery float voltage, about 2.2V per cell, determined. Considering the charging and discharging platform of the battery, the actual allowable input voltage range of the device is generally wide, at least reaching -40V~-57V for normal operation. Usually the limit is -36V~-62V. Of course, lithium batteries have also been used in the communication industry in recent years, and are not written in detail.
For the IT industry data center, AC110 or 220 power supply is generally used, and almost no -48V power supply equipment is seen. The reason is mainly that IT equipment has evolved from such devices as computers, and there is no history of using DC power. In addition, the power density of IT equipment is increasing, and the power density is 200 watts per U, or 5000 watts per frame. In recent years, high-density data centers have 9kw per frame, and some devices have designed more than 10KW of power capacity in a chassis of about 15U. At such a density, using a 48V supply voltage, power wiring and terminals with hundreds of amps of overcurrent capability are also quite difficult to implement.
The use of AC power supply, as a reliability requirement, always requires the deployment of an uninterruptible power supply system. The problems caused by this are: Low energy efficiency, AC mains conversion by AC-DC, to DC of 300-400V, for battery packs Float (or maintain flywheel operation for flywheel UPS), then perform DC-AC inverter to the device. The device power is again subjected to AC-DC (APFC)/DC-DC conversion to the target voltage. Even if the conversion efficiency reaches a high level of 92%, the overall efficiency is less than 85%; in addition, the UPS construction cost is high; and the interconnection system has the problem of grid connection difficulties.
In recent years, high-voltage DC power supply is a relatively hot trend in the data center energy industry. The use of DC power supply of 240-270 or so, low construction cost and high energy efficiency mean lower operating expenses. With the popularity of IT equipment supporting high-voltage DC power supply, it should be a development direction.