What is active Power Factor Correction (PFC)?

Active Power Factor Correction (PFC) is an advanced technique for the synchronization of the voltage and current cycles on incoming AC mains power. It is utilized to maximize the efficiency and quietness of pre-power supply current rectification.

In addition to all of their inherent advantages, switch mode power supplies in JRDG power amplifiers, including the new Model 625 class A/B stereo power amplifier,  maximize their performance when fed a truly noise free DC power stream at up to 385V. The advanced JRDG front ends incorporating PFC generate an invariant DC current and voltage for the switch mode power supply, without any residual voltage or current fluctuations, ripples, or unwanted noise, independent from the typically grungy AC mains grid.

Jeff Rowland pioneered the use of active PFC in high-end audio amplification in 1999 with the model 10 and model 12 power amplifiers. Today, JRDG incorporates further refinements of this technology in its reference amplifiers, including the Model 625 class A/B stereo power amplifier, and the Model 301 monoblock power amplifier, as well as the Continuum 500 integrated power amplifier.

“Power Factor,” a figure of merit term used to describe the ratio of “real” to “apparent” power, is the measure of how much AC power a device actually utilizes for its intended purpose in comparison to the amount of power it draws.  In other words, this is the measure of how much power a product consumes in comparison to the amount of work it produces.  The ideal power supply would have a Power Factor of “1,” or be 100% efficient and use exactly enough power to do only the work it is intended to do.

Conventional, as well as most switch-mode power supplies used in other audio amplifiers, pull AC current from the wall in fast rise time pulses 100 or 120 times per second.  These high-current pulses, drawn only during the time the AC line voltage approaches peak, produce high harmonic content noise currents that in turn distort the AC mains current, thereby producing an inefficient power factor of about 0.6.  These harmonic currents circulate back into the AC power line and also pollute the current supplying the rest of the audio system.  The problem is compounded by other audio components in the system, as they may also be producing similar harmonic noise currents. 

Conversely, the design of the Model 625, the Model 301, and the Continuum 500 power supplies, front ended by PFC, eliminate the pulses of current drawn from the wall and instead draw a continuous, pure sinusoidal flow of AC current which is in phase or “in step” with the AC line voltage, resulting in the elimination of circulating harmonic noise currents, both within the amplifier and throughout the rest of the audio system.  This results in a power factor of approximately 0.99. 

A high speed switch in the circuit extracts energy at 100 KHz from an inductor during the entire cycle of the AC sinusoid. Ensuing DC Energy is then stored temporarily in a large capacitor bank for further normalization, prior to feeding the rest of the amplifier.  In addition, the amount of harmonic current noise and distortion on the AC line is so significantly reduced, that it has also an audible beneficial effect on the rest of the system.

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Last Updated
24th of October, 2010

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