About PFC

Essay about PFC - "for love or money?"

Back in good old times, galvanically isolated stabilized power supplies used to be designed with a transformer, which worked on a base mains frequency of 50 Hz (for land equipment) and 400 Hz (for aerial equipment). No one would bother about impulse consumption from the primary network - isolating low-frequency transformer would "smooth" the current impulses over time, lowering their amplitudes. Also there were quite few of secondary power supplies connected to one line of the primary network.

High-frequency switch-mode power supplies came to replace the previous generation (the ones with low-frequency transformers), to decrease copper usage in order to reduce weight and dimension and to increase efficiency. The revolution was inevitable in the environment of rapid requirements increase in all kinds of power supplies, working with AC mains. Semiconductors were developing quickly.

Already in the early 90s it became obvious that there could exist market power supply sectors for the most part based on marketing principles, then technical practicality.

There are examples to this.

For example, the arrival of uninterruptible power supplies (UPS) for personal and other computers. The computers, in particular, that had switch-mode AC/DC power supplies at the mains inputs, which could natively and safely operate from constant voltage of 300 VDC. Nonetheless, a large industry for mass-production of AC/AC UPS was born, devices that would provide alternating current of 220 VAC. Millions of pieces of such UPS were produced and are still being produced.  This was and still is a marketing conspiracy to boost the sales. Only recently computers (notebooks) have received its own uninterruptible power source in form of a DC battery.

In general, marketing scam was a success.

Why such a long intro might you ask. Because there was a very similar story with PFC. Power Factor Correction came during the time of over-production of AC/DC power supplies and an ingenious marketing trick was needed to revive the sales and to support the production.

Certainly, there was some technical premise. If there are many pulse devices connected to one power line and operating at the same time - it may cause enormous pulse currents far from resembling sinusoidal voltage shape. Such currents, in contrast to quite tolerable current impulses of mains frequency, may reach times larger coefficient of form than in the older power supply systems. Of course, a discussion about increased effective current value was started, and everyone was afraid for durability of the electricity lines (!). May be it was necessary to increase the cross-section of the wiring in all flats, houses and factories? Scare factor was pretty powerful. But in practice it wasn't that scary. Two factors were against the fear - first one was the significant effect of impedance of very real mains lines, and second one was inner impedance of a primary power source. And anyways, the impedance is by large margin defined by an output impedance of the same old transformers that were still in placed in the power lines. The transformers that up to this day no one managed to replace.

In short, power dissipation in the electricity wires increased by a few percents, and reserve margin in the wires cross-section, defined by the standards, already dispelled the fear long ago. So in the end, all the may's marked above didn't really come true.

It must be said, that there is more and more computers and simple diode lamps being connected to one power line, but at the same time the electricity lines are being modernized and the copper isn't spared for wires.

Certainly, the equipment is diverse and very quickly evolving, however there are certain applications where PFC is a must.

However, recall the time when a new regulation forbid use of lead in solders - requiring to replace the lead with no less harmful elements. Thus now the whole world is struggling - solders are faulty and unreliable, costs for new machines (i.e. high-temperature or inert gas soldering ovens) have increased. However in application where solder quality is critical - in medicine and military equipment - there lead additives are allowed. Who won? Sellers of solder and other chemicals and machinery manufacturers became much richer, but devices with large number of solder points lost.

And this is love not for love, but money. For your money.

Arrival of PFC is similar - at some points regulations were made, requiring everyone to use power supplies with PFC. But still in many cases this is not for love but money.

So.

Excluding PFC decreases the amount of AC/DC power supply components by 30-40 %, i.e. dramatically increases MTBF and allows for other components to be spaced out better in the dedicated dimensions of the unit's casing, without local overheated spots caused by compact placement.

Excluding PFC increases power supply efficiency by 3-5 %, which in some cases brings undeniable advantages for the cooling systems.

Excluding PFC improves EMC of the power supply with the equivalent filtering components or allows to reduce input filtering. Importantly - rejecting PFC may create a discount.

However, when ordering, consult with your system specialists before excluding PFC, they can correct you with their authority. Yes, I won't refuse to consult you in difficult cases either. Write to us.

General designer of AEPS-GROUP Alexander Goncharov.

P.S.

It's important to consider that PFC allows to consume close-to-sinusoidal-shape current from a sinusoidal mains voltage. When is PFC necessary?

  1. When there is dense concentration of AC/DC units connected to one (!) power line directly, i.e. to the output winding of a powerful transformer, placed at the inlet of a compound. Typical example - LED lighting in amount of thousands and tens of thousands of pieces in one hall. Or large computer networks of hundreds and thousands. Or bitcoin mining facility. Synchronous effect of pulse current consumption may indeed result in mains power line overloading.
  2. When power devices are directly connected to the output windings of voltage generators, i.e. airplane mains of 115 VAC or land mains of 380 VAC. Generators react poorly to impulse currents, stop providing full output power and start overheating.

In such cases don't hesitate - certainly PFC is objectively needed.

It should be noted that in certain cases there is a short-term need for AC/DC units to work at decreased input voltage, by 30 % or more. Or there is a possibility of exporting the product to countries like USA, Japan, Brazil. I.e. there is a requirement of having an ability to operate from both high and low input voltage. Here PFC can be very useful.