I came across this question:why boost PFC topology is the most used?

Now I ask myself, should I do PFC too? My system is a servo with diode bridge rectifier and different current ratings. Very price sensitive.

So I thought, I can do a boost PFC in place of inrush current limit (resistor and relay). So at least in my mind it's allowed. But what other benefits will that do for the system and for the user?


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  • \$\begingroup\$ Hard to tell without knowing what it is and where it is, for a lot of applications there are regulations in place that outright require PFC. \$\endgroup\$ – PlasmaHH Jun 30 '17 at 10:11
  • \$\begingroup\$ Yes, but for the sake of the question, no regulation and virtually any application. In other words, i want to understand the different cases when pfc is better and others when it doesn't matter or is too expensive to force the client to pay for it. \$\endgroup\$ – Gregory Kornblum Jun 30 '17 at 10:26
  • 1
    \$\begingroup\$ That is pretty broad then, one could write many books about it. Generally PFC is there to improve the PFC, so when there is nobody demanding a certain PF, then there is no reason to do PFC other than to be nice. \$\endgroup\$ – PlasmaHH Jun 30 '17 at 10:30
  • \$\begingroup\$ Ok, that may be the ultimate question. So no way to improve whole system efficiency, or like stabilize better the DC voltage? \$\endgroup\$ – Gregory Kornblum Jun 30 '17 at 10:32
  • \$\begingroup\$ PFC will decrease whole system efficiency, rather than increasing it. In typical topologies inrush current limiter is still needed, because the bulk DC link capacitor is connected to bridge rectifier via PFC's inductor and diode. An exeption is the single stage flayback PFC, where you can have only about 1uF at the input, but this is applicable up to 50-100W max. Your question is too broad and does not contain at least a block schematic of the input stage, so you can't expect valuable answers. \$\endgroup\$ – Todor Simeonov Jun 30 '17 at 10:38

The main benefit of a PFC is being allowed to sell your product and for the customer to be able to use your product. That's a fairly big one. This requirement kicks in at a predefined power level.

Other than that it makes it easier to deal with universal input as others remarked and generally makes for a nicer operating profile as your power conversion is not pulsed. That's mainly relevant for higher power conversion, in other cases its really just added cost and complexity.

For inrush current you may want to consider a triac instead of a relay.

For background this kind of requirement originates with fluorescent lighting which is a nasty load for electric grid. Basically drawing lots of current to uncompensated inductive (or capacitive) load throws off the mains theta which more or less creates load for no benefit. For SMPS the deal is using the whole sine wave and not just the top n percent of it which also messes up the power grid

The power quality side of things is a bit more complex having to do with real and "imaginary" load but it comes down to power distribution no likey.

  • \$\begingroup\$ Your product may require to comply with power factor regulations such as IEC 61000-3-2. \$\endgroup\$ – DiMorten - Jorge Chamorro Jun 30 '17 at 15:50
  • \$\begingroup\$ Just like fluorescent lighting, LED lighting circuits are also nonlinear loads which draw pulsating current from power distribution system. \$\endgroup\$ – DiMorten - Jorge Chamorro Jun 30 '17 at 15:51
  • \$\begingroup\$ @JorgeC you can perfectly well do a constant current with LEDs but the SMPS driving circuit has the usual only-peak-of-sine-wave caveat. Without PFC that is. \$\endgroup\$ – Barleyman Jul 1 '17 at 19:48

Good comments and answers for this Q.

In addition to regulatory issues driving the need for PFC, there are also marketplace driven demands. Customers with a large energy consumption profile are often charged a premium by their power utility for their var level. While this may force them to implement mitigation for their current installed base, new capital purchases will also be evaluated on the basis of their PFC. This can provide a competitive advantage for suppliers that have anticipated this criterion.


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