Diagram of a PFC controller circuit

Active PFC Boosts Power Supply Efficiency

What is PFC?

Power Factor Correction (PFC), a feature that makes a power supply more efficient. With PFC more and cleaner power is available for your devices.

When processing energy for your devices, a power supply is plugged into an electrical socket the electricity (input power) goes through a series of components. These components use some of the electricity; the rest gets fed to your devices (output power). The power that’s used by devices is called real power that is used for “useful work.” The power used by the components is referred to as reactive power.

  • Real power is the power used by PCs and other devices to perform useful work. It’s measured in Watts (W).
  • Reactive power is the power used by components (such as transformers) to enable the useful work. It’s measured in Volt-Amp-Reactive (VARs).
  • Apparent power is the sum of real power and reactive power. It is measured in Volt-Amps (VA).


Power factor is expressed as the ratio of real power absorbed by the load to the apparent power flowing in the circuit. Power Factor Correction increases the power factor of a load, which improves efficiency. While correction could be either passive or active, modern computer power supplies use Active PFC.

Power factor values in AC circuits fall between 0 and 1. The higher the number, the less energy is wasted. The power factor of a typical switching power supply is 0.6 to 0.7, while the power factor of a corrected power supply is typically 0.95 or greater. The less reactive power you need to enable useful work, the more can be used for doing useful work, so look for power supplies with power correction as close to one as possible.

While increasing efficiency, Active PFC produces cleaner power with less electrical noise and less power wasted as heat (and its removal).


PFC in Medical Power Supplies

Medical power supplies with PFC allow medical facilities to operate more equipment off the same line because the peak current is less for the same power. Efficiency is important, but reliability is even more important. Medical power supplies need to be tested to and pass the EN 61000-3-2 specification for power line harmonics, and the EN 1000-3-3 specification for power line flicker. To comply with the harmonic standard, it is necessary to add PFC circuitry to the power supply.

For your devices, particularly medical devices, choose power supplies with Active PFC; you’ll get more and better power.


At RAM Technologies, we understand the importance of efficient, reliable power for medical devices. Our power supplies feature proprietary Active PFC with DC-to-DC pulse-width modulation that boosts input power factor to a typical 0.99.