USB is the abbreviation for Universal Serial Bus, which means "Universal Serial Bus" in Chinese. It is a new interface technology used in the PC field. As early as 1995, there have been PCs with USB interfaces, but due to the lack of software and hardware support, these PCs are idle USB interfaces are not used. 1998, with the built-in support module for USB interfaces in Microsoft Windows 98, coupled with the increasing number of USB devices, USB interfaces have gradually come into the practical stage.
In the past few years, with the popularity of a large number of personal computers supporting USB, USB has gradually become the standard interface for PCs. In the host (host) side, the latest PC almost 100% support for USB; and in the peripheral (device) side, the use of USB interface devices are also increasing day by day, such as digital cameras, scanners, joysticks, tape and floppy drives, image devices, printers, keyboards, mice and so on.
The reason why USB devices are used in a large number of applications is that they have the following advantages:
1, hot-swappable. This allows users to use external devices, do not need to repeat the "shutdown à parallel port or serial cable connected à power on" such action, but directly in the PC power on, you can plug the USB cable to use.
2, easy to carry. USB devices are mostly "small, light, thin" for the user, the same 20G hard drive, USB hard drive than IDE hard disk to lighten the weight of half, in want to carry a lot of data, of course, USB hard drive will be the first choice.
3, standardization. We are common IDE interface hard disk, serial port mouse and keyboard, parallel port printer and scanner, but after the USB, these applications peripherals can be connected to the PC with the same standard, then there is a USB hard disk, USB mouse, USB printer, and so on.
4, can be connected to multiple devices. USB on the PC often has multiple interfaces, can be connected to several devices at the same time, if connected to a USB HUB with 4 ports, you can connect to 4 USB devices, and so on, as far as possible to connect down to your home at the same time connected to the device in a PC without any problems (Note: up to 127 devices can be connected to). II. What is UPS ? First, the UPS and its working principle of the introduction UPS is the English abbreviation for Uninterruptible Power Supply, meaning "uninterruptible power supply", is a kind of containing energy storage devices (commonly battery), inverter as the main component of the Constant voltage and frequency uninterruptible power supply, it can solve the existing power outages, low voltage, high voltage, surge, noise and other phenomena, so that the computer system operation is more secure and reliable. Now it has been widely used in computer, transportation, banking, securities, communications, medical, industrial control and other industries, and is rapidly moving into the family. Below, let us first briefly understand the working principle of UPS. When we do not use the UPS, PCs, printers and other terminal equipment is directly connected to the utility to use, with the UPS, PCs, printers and other terminal equipment connected to the UPS to use, and the UPS then access to the utility. When the utility input is normal, the UPS will be stabilized utility voltage supplied to the terminal equipment (relative to the UPS, we will be these terminal equipment called loads) to use, at this time, the UPS is an AC utility voltage regulator, at the same time, it is also charging their own built-in batteries; when the utility interruptions (for example, blackouts), the UPS will be built-in battery power immediately, the inversion method to continue to supply the load through conversion 220V AC power, so that the load to maintain normal work and protect the load of software and hardware systems from damage. Second, the impact of utility power on home PCs and their terminal equipment If our PCs, computer networks and other equipment do not use a UPS, and what will be affected? Many people have a common misconception that we use the utility power, in addition to the occasional power outage, are continuous and constant. This is not the case. The utility system as a public **** power grid, connected to thousands of various loads, some of the larger inductive, capacitive, switching power supply loads not only from the grid to obtain electricity, but also in turn on the grid itself, deterioration of the power grid or local grid power supply quality, resulting in utility voltage waveform distortion or frequency drift. In addition, accidental natural and man-made accidents, such as lightning strikes, transmission and transformation system disconnection or short-circuit, power plug ground wrong unplugging, etc., will jeopardize the normal supply of electricity, thus affecting the normal operation of the load. In particular, it is necessary to point out that PCs, network equipment, communication systems, medical equipment, etc. are very sophisticated electronic equipment, the impact of their performance is particularly prominent. For PCs, monitors and hosts require a normal power supply to work. In particular, memory, which is a storage device that relies on electrical energy, requires constant refreshing action to maintain the stored content, and once the power is cut off, the saved content immediately disappears. If abnormal power failure results in the information in the memory not being saved to the hard disk and other storage devices in time, it will cause the information to lose its value because it is completely lost or becomes incomplete, thus wasting a lot of work energy and time; and operating systems like UNIX and Linux (nowadays, many computer enthusiasts use this kind of operating system), if they are not shut down normally, the system information in the memory is not written back to the hard disk, may also cause the system to crash, can not start again; In addition, the hard disk in the computer, although the application of magnetic storage media, will not be due to power outages and the loss of information, but a sudden power failure will make the hard disk is reading and writing the work of the physical head damage, or the system files in the maintenance of the file system, resulting in the file allocation table error, so as to make the hard disk to generate a bad sector, serious, and even will cause the whole Hard disk scrap; In addition, most of the current operating system can set the virtual memory, due to a sudden power failure, so that the system can not cancel the virtual memory, resulting in hard disk "information fragmentation", not only a waste of hard disk storage space, but also lead to slow machine operation; computer power supply is a kind of rectifier power supply, too high a voltage may cause rectifier burnout. The computer power supply is a rectifier power supply, too high voltage may cause the rectifier burned. The voltage spike and transient overvoltage, as well as the power supply noise and other disturbances may enter the motherboard through the rectifier, affecting the normal operation of the machine, and even burn the host line. In general, the standard sine wave (220V, 50Hz) is an ideal state, but in reality, according to the test of power experts, the power grid often occurs and the computer or precision instruments to interfere with or cause damage to the following conditions: surge, high-voltage spike pulse, transient overvoltage, voltage sag, wire noise, frequency drift, continuous low voltage, utility interruptions, and so on. Interruptions, etc. 1. power surge (Power Surges): refers to the output voltage RMS value is higher than the rated value of 110%, and the duration of one or more cycles. Power surge is mainly due to the grid connected to large electrical equipment shutdown (such as common household air conditioning shutdown), the grid due to sudden unloading of high voltage (we will have such a personal experience: in the evening from 6:00 to 9:00 or so of the time period, is the peak of the power supply, the utility voltage is generally low, the home lighting is darker, the peak of the power, such as in the evening 10:00 (Around 10:00 pm, you will find that the lighting in your home suddenly flashes and is much brighter, which is one of the most common surge phenomena we see in our daily lives). 2. High Voltage Spikes (High Voltage Spikes): refers to voltages with peaks of up to 6000v and durations ranging from one ten-thousandth of a second to one-half of a cycle (10ms). This is mainly due to lightning strikes, arc discharges, static discharges or switching operations of large electrical equipment. 3. Transient overvoltage (Switching Transients): refers to the peak voltage of up to 20000V, but the duration of the pulse voltage bounded by millionths of a second to ten thousandths of a second. Its main reason and may cause damage similar to the high-voltage spike pulse, just in the solution will be different. 4. Voltage sag (Power Sags): refers to the utility voltage RMS value between 80% and 85% of the rated value of the low voltage state, and the duration of one to several cycles. Large equipment start-up, large motor start-up, or large power transformer access can cause this problem. 5. Electrical Line Noise (Electrical Line Noise): refers to radio frequency interference (RFI) and electromagnetic interference (EFI), as well as a variety of other high-frequency interference. The operation of the motor, the action of the relay, the work of the motor controller, radio transmissions, microwave radiation, and electrical storms, etc., will cause line noise interference. 6. frequency shift (Frequency Variation): refers to the utility frequency change of more than 3Hz. This is mainly due to the unstable operation of the emergency generator, or by the frequency of unstable power supply. 7. sustained low voltage (Brownout): refers to the utility voltage RMS value is lower than the rated value, and continue for a long time. Its causes include: large equipment startup and application, main power line switching, starting large motors, line overload (many parts of our country have this problem). 8. utility interruptions (Power Fail): that is, we usually encounter power outages. The causes are: tripping of circuit breakers on the line, interruption of the utility supply, grid failure. III. Classification of UPS UPS has evolved from rotating generators in the 60s to today's static fully electronic circuits with a degree of intelligence, and continues to evolve. At present, UPS generally refer to stationary UPS, according to its mode of operation can be divided into backup, online interactive and online three categories. 1. Backup UPS: When the utility power is normal, directly from the utility power to the load power supply, when the utility power exceeds its operating range or blackout, through the conversion switch to the battery inverter power supply. Characterized by: simple structure, small size, low cost, but the input voltage range is narrow, the output voltage stabilization accuracy is poor, there is a switching time, and the output waveform is generally a square wave. The schematic diagram is as follows: 2. On-line interactive UPS: When the utility power is normal, directly from the utility power to the load power supply, when the utility power is low or high, through the UPS internal voltage regulator line regulator output, when the utility power is abnormal or blackout, through the conversion switch to the battery inverter power supply. It is characterized by: a wide range of input voltage, low noise, small size and other characteristics, but there is the same switching time, but compared with the general backup UPS, this model has a stronger protection function, the inverter output voltage waveform is better, generally sinusoidal. The schematic diagram is as follows: 3. On-line UPS in the utility power normal, rectified by the utility power to provide DC voltage to the inverter work, the inverter to the load to provide AC power, in the utility power abnormal, the inverter from the battery to provide energy, the inverter is always in the working state, to ensure that the uninterrupted output. It is characterized by an extremely wide input voltage range, no switching time and high accuracy of output voltage stabilization, which is especially suitable for occasions with high power requirements, but at a higher cost. At present, the power greater than 3KVA UPS is almost always online UPS. schematic diagram as follows: UPS according to the size of the output capacity is divided into a small capacity of 3KVA, small and medium-capacity 3KVA ~ 10KVA, medium and large-capacity 10KVA or more. UPS can be divided into three categories according to the input/output mode: single-phase input/single-phase output (referred to as single in single out), three-phase input/single-phase output (referred to as three in single out), three-phase input/three-phase output (referred to as three in three out). For the user, three-phase power supply and load distribution of utility power is easy, each phase is responsible for a portion of the load current, and therefore, high-power UPS more than three-phase input/single-phase output or three-phase input/three-phase output power supply mode. Backup UPS is mainly used to provide power protection for a single PC, and is characterized by small size, low price, and simple operation, which is very suitable for home use, so when you buy a UPS for your home computer, please buy a backup one. Online UPS can solve almost all common power problems, when there is utility power, the function is to stabilize the voltage and prevent power fluctuations from interference, because of its better function, so its cost also rises with the enhancement of the performance, the price is much more expensive than the backup UPS. On-line UPS is mainly used for power requirements are very strict some computer equipment, medical equipment, etc., generally used in series with a number of external batteries to extend the power supply time, more than the unit configuration. Intelligent UPS is a major development trend of today's UPS, with the application of UPS in the network system, network managers emphasize the entire network system for the protection of the object, I hope that the entire network system in the power supply system failures, can still continue to work without interruption. Therefore, the UPS internal configuration microprocessor to make it intelligent is the new trend of the UPS, UPS internal hardware and software combination, greatly improving the function of the UPS, you can monitor the operation of the UPS work status, such as: UPS output voltage frequency, grid voltage frequency, battery status and fault records. Can also be detected through the software on the battery, automatic discharge and charging, as well as remote control of the switch and so on. Network managers can analyze the quality of power supply according to the information, according to the actual situation to take appropriate measures. When the UPS detects an interruption in the power supply grid, the UPS automatically switches to the battery power supply, and immediately notifies the server to make preparations for shutdown when the battery power supply capacity is insufficient, and shuts down itself before the battery is exhausted. Intelligent UPS through the interface to communicate with the computer, so that network administrators can monitor the UPS, so the function of its management software is extremely important.