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Uninterruptible Power Supply (UPS)
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An Uninterruptible Power Supply (UPS) is an electrical apparatus that provides emergency power to a load when the input power source or mains power fails.
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| A UPS differs from an auxiliary or emergency power system or standby generator in that it will provide near-instantaneous protection from input power interruptions. When the power failure period is longer than the UPS can support, it properly shut down the protected equipment. |
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| UPS units are also capable in correcting common utility power problems, such as voltage spike or sustained overvoltage, momentary or sustained reduction in input voltage, voltage sag, noise, instability of the mains frequency, etc. |
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Generally, there are three categories of modern UPS systems:
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On-line UPS
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| An on-line UPS uses a "double conversion" method of accepting AC input, rectifying to DC for passing through the rechargeable battery (or battery strings), then inverting back to 120V/230 V AC for powering the protected equipment |
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Line-interative UPS
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A line-interative UPS maintains the inverter in line and redirects the battery's DC current path from the normal charging mode to supplying current when power is lost.
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Standby UPS
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In a standby ("off-line") system the load is powered directly by the input power and the backup power circuitry is only invoked when the utility power fails.
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