Pure Sine Wave vs. Modified Sine Wave

In regard to output waveform, two types of UPS systems exist—the kind that produce a pure sine wave and the kind that produce a stepped approximation of a sine wave, also known as a pulse-width modulated (PWM) sine wave. The main difference between pure sine wave and modified sine wave systems is that a pure sine wave system in battery backup mode is guaranteed to produce a cleaner output for any piece of equipment connected to it, whether it’s a computer at a workstation or a server in a data center. The same cannot be said of a modified system, which produces a step, or PWM, sine wave output. Its output is choppier and provides equipment with a less stable output waveform.

Pure Sine Wave

pure sine wave



  • smoother and cleaner output for sensitive equipment
  • improves equipment performance and efficiency
  • approximately two times the cost of a comparable modified sine wave UPS system

Modified Sine Wave

modified sine wave



  • approximately half the cost of a pure sine wave UPS system
  • less smooth and stable output
  • decreased equipment performance and efficiency

modified and pure sine wave compare

It’s important to understand that both types of UPS system produce true sine wave output more than 99% of the time. It is only during a power failure, when the UPS is producing power from its battery reserves, the output waveform is a concern. Also keep in mind that typical applications for pure sine wave UPS systems involve the protection of critical server, network, medical and telecommunications 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.

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