If the supply of the computer's power supply is not normal interrupt or current unstable, uninterruptible power supply UPS (Uninterruptible Power Supply) will assume the function of the temporary emergency power supply, so that the computer will not be forced to the loss of data due to power outage, or causedamage.UPS itself can support tens of minutes of power supply buffer time, the user is thus able to complete the archive file, and so the task at hand, normal shutdown, thereby enabling data to be preserved. Computer during data operations or records, every minute and second in the quite sophisticated processing status, once the main power supply is suddenly cut off, as if the car speeding on the highway without warning and rapid braking, or are preparing to land the jetthe sudden loss of power generally cause major system damage. The principle of UPS power supply when the mains is normal, the machine will mains alternating current (AC) is converted to direct current (DC), and battery charging. Once the UPS has detected abnormal or power off the mains voltage, and then stored in the battery current into alternating current supplied to the load continues to be used in order to achieve the functionality of uninterruptible power. UPS is mostly a box shape, mainly by a sealed lead-acid battery monitoring software and relay equipment posed more sophisticated design, mains battery or converter can convert time becomes shorter, canmake up generators or other emergency power outage shortcomings too long. UPS does not apply due to the limited capacity of the battery, the power consumption of peripherals. UPS divided into line (on-line), off-line (off-line), staggered (line-interactive) 3 categories, staggered characteristics between online and offline, but its operating characteristicsshould be classified in the off-line.The so-called on-line UPS, when the normal electricity supply, mains filter circuit and surge absorption circuit is divided into two circuits to operate simultaneously, one via the charging circuit charging the battery pack, and the other is rectifiedloop, as the converter input, and then after the conversion of the inverter to provide power to the load; abnormality occurs if the mains, the inverter input is changed from a battery pack to supply, converter continuing to provideelectricity.Therefore, on-line UPS output entirely by the inverter to supply, without conversion time, attenuation capability of mains noise, surges, the output circuit is the most stable, and only when UPS failure or overheating, power willoutput from the bypass. However, the complex structure of on-line UPS, the cost is higher. Off-line UPS when normal electricity supply, mains filter circuit and surge absorption circuit filter noise directly supply system power, in the meantime once passing by a charging circuit to charge the battery pack; at this time if the mains voltageunstable, then the output voltage and the mains as unstable. Experiencing power outage, will via the converter to alternating current, power is transmitted by the battery. Thus, off-line UPS has two sets of power used interchangeably, the two groups need to convert the time when the power is switched alternately, the conversion time will make certain equipment caused the crash, the attenuation of mains noise and surge protection less capable .However, off-line UPS structure is simple, small size, light weight, therefore lower costs. line-interactive UPS principle not far off-line UPS, its main use MPU as the control center can automatically adjust the voltage when the mains input is too high or too low, the MPU automatically switches to the output of the converter, and then startregulator adjustment, wait until utility power is restored to normal, the supply system. The point of difference is that the line-interactive UPS instant transaction will immediately convert the battery power supply, to ensure a stable voltage supply, and off-line UPS is until the voltage transactions above a certain range, only because the mains voltage is detected automatically by the MPU, start the regulator circuit.line-interactive UPS mains noise attenuation surge protection capabilities between on-line and off-line UPS, power conversion time, alternating complex structure, high cost, and bi-directional converter design sobattery recharge time is shorter.