# Is there any advantage if the PFC inductor is split in between +ve and -ve input line?

While doing the reverse engineering this is what I observed.

The PFC inductor is having 8 set of pins , out of which 4 are shorted to input (+) and 4 are shorted to GND (input return). Obviously , there is no continuity between the two sets (Figure 2). Had it been a normal PFC inductor (as per Fig 1), I should have seen continuity between all pins of the inductor.

I am assuming the PFC inductor is split into 2 - Between +ve line and Return line.

I am not sure what is the advantage of splitting them? May be they are coupled- Would it provide any area/height advantage?

• AC input directly from utility distribution is likely to be grounded. That would prevent the DC side from being grounded. If the AC supply is grounded, protection of the circuit would benefit from impedance in the DC circuit divided between the positive and negative sides,
– user80875
May 3 at 12:01

If you make them coupled the net inductance will not be the sum of them. And analysing the circuit may be a bit complicated.

If you have some size issues (e.g. max height) splitting the boost inductor may help but putting one to positive side and another to negative may not be necessary. It also may create some trouble (e.g. control and driving).

Unless it's an interleaved PFC pre-regulator, using split inductors does not bring significant advantages, methinks.

No advantage. The opposite: you need certain sum inductance. You get it with less wire if there's only one coil (the inductance is proportional to the square of the number of the turns). You must also calculate the cost of non-saturating magnetic core. That depends heavily on the market situation, so I skip it.

ADD This answer needs rewriting. It's based on total missing the actual point: The splitted inductor is not planned, it exists. It isn't there without a reason.

One easy guess: The other (=set B in fig 2) is not at all an inductor, it's current sensing resistor. But without having the device in my hands this is only a guess.

If the inductors are in the same core there's no difference in the need of turns. In addition the extra amount of the wire in 2 separate coils can well be so small that its price isn't a problem. I guess the reason is the reduction of RF emission to mains AC wires when there's some 3rd way capacitive connection from the poles of Vo to the ground. But proper analysis is still waiting to be done.

• Sorry, Did not understand this sentence- "You get it with less wire if there's only one coil" May 4 at 2:35
• Lets's assume a single inductor with wanted inductance needs 100 turns of wire with a certain core (=type X). If you have the same total inductance as a sum of 2 identical inductors made on 2 identical type X cores, they both need 71 turns the same wire and instead of only 1, you have 2 pieces of type X cores. May 4 at 8:02
• Thanks. Ok got it, Even if they are coupled the total turns comes out to be higher than a single inductor. May 5 at 2:53