Pure sine wave vs. modified sine wave explained

UPS systems produce two types of output waveforms when running on backup battery power:

1. Pure sine wave: A smooth, consistent waveform that closely matches the utility power supplied by the grid.

2. Simulated or Modified sine wave: Also known as a pulse-width modulated (PWM) sine wave, this is a stepped approximation of a pure sine wave.

Under normal conditions, when utility power is stable and within acceptable voltage and frequency ranges, the UPS can easily power through to connected devices. Since utility power is typically a pure sine wave, this is what connected equipment expects to receive.

However, when a power disturbance occurs—such as a blackout, voltage fluctuation, or frequency shift, the type of waveform it produces becomes critical.

Pure sine wave UPS: Delivers clean, stable power during battery operation, making it suitable for sensitive electronics like servers, lab equipment, and desktop computers.
Simulated sine wave UPS: Produces a choppier, less stable waveform that may not be ideal for certain devices, especially those with active PFC (Power Factor Correction) power supplies.

Note: A "stepped sine wave" is essentially the same as a "square sine wave" in this context.

Pure sine wave

PROs

Smoother and cleaner output for sensitive equipment
Improves equipment performance and efficiency

CONs

Approximately two times the cost of a comparable modified sine wave UPS system

Modified sine wave

PROs

Approximately half the cost of a pure sine wave UPS system

CONs

Less smooth and stable output
Decreased equipment performance and efficiency

It’s important to understand that both types of UPS system produce true sine wave output more than 99% of the time. Additionally, typical applications for pure sine wave UPS systems involve the protection of critical server, network, medical and telecommunications equipment or electronic equipment that is particularly sensitive to input power, such as lab test equipment. Modified sine wave UPS systems typically protect PCs, home entertainment systems, A/V components and media centers.

Looking for a pure sine wave or modified sine wave UPS systems? Browse our models.

Modified sine wave UPS systems

Pure sine wave UPS systems

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