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How does an uninterruptible power supply (UPS) work?

by informsarakhan
uninterruptible power supply (UPS) work

An uninterruptible power supply (UPS), also known as a battery backup. Provides backup power when normal power fails or the voltage drops to an unacceptable level. The UPS ensures a safe and orderly shutdown of your computer and connected equipment. The size and design of the UPS determine how long it can provide power.

UPS Topologies

Different UPS topologies offer a certain level of power protection. An inverter refers to one of three topologies: redundant, line-interactive, and double-conversion.

The redundant topology

It is the simplest of the inverters. A backup UPS switches to battery mode in the event of a general power problem, such as a power failure, voltage drop or surge. When the incoming mains voltage falls below or exceeds a safe level, the UPS switches to DC battery power and then converts it to AC power to operate the connected equipment. These models are designed for consumer electronics, entry-level computers, point-of-sale systems, security systems, and other basic electronic equipment.

Inline interactive UPSs

Inline interactive UPSs use technology to correct minor voltage fluctuations (under and over voltage) without going through the battery. This type of UPS has an autotransformer that regulates low voltage (e.g., during power outages) and high voltage (e.g., during power surges) without the need for a battery. Inline interactive UPS models are typically used for consumer electronics, PCs, gaming systems, home theater, networking devices, and servers in the low to medium power class. They provide power during events such as power outages, voltage drops, surges, or overloads.


A double-conversion inverter (in-line inverter) provides continuous, clean, near-perfect power regardless of the state of the incoming power. Such an inverter converts the incoming AC voltage to DC and then back to AC voltage. UPS systems with this technology operate 100% of the time on isolated DC and have no transition time, as they never have to switch to DC. Dual-conversion APC UPS systems are designed to protect critical IT equipment, data centers solutions, high-end servers, large telecommunications and storage systems, and advanced networking equipment from damage caused by power outages, voltage sags, surges, frequency noise, frequency fluctuations, or harmonic distortion.

UPS output waveforms

Depending on the system design, UPSs have a sinusoidal or simulated sinusoidal output waveform.

Sine output:

The highest quality output waveform is the sine wave, which is a regular, repeating oscillation of AC current. Enterprise level UPS systems generate sine wave voltages to power sensitive electronic equipment. The sinusoidal output waveform ensures that equipment using power supplies with active PFC does not fail when switching from mains to the battery.

Simulated Sine Output:

Approximate sine output waveform. It uses pulse wave modulation to produce a stepped, quasi-sine waveform. That provides more economical battery backup power for devices. That does not require a sine wave output. The technology used to generate this type of output is less expensive to manufacture. Often used in redundant and interactive in-line UPS systems.

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Read: Are you looking for an uninterruptible power supply system?


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