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Average current mode PFC controller

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treez

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Hello,
Why do they call “Average Current Mode PFC controllers”, “Continuous current mode PFC controllers”?

After all, they may well operate totally in Discontinuous mode.

Eg the following NCP1653 is “incorrectly” called a “continuous mode pfc controller”
http://www.onsemi.com/pub/Collateral/NCP1653-D.PDF
 

mtwieg

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It's just a description of the intended mode of operation. Obviously it can be made to operate in DCM at very light load.

I don't see any conflation between average/continuous mode in that document.
 
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Thanks, the thing is, as you know, for say a 150W PFC'd power supply , its often a good idea to operate it in discontinuous mode even at max load.
(and use an Average current mode controller [aka CCM mode controller] to do it)
DCM makes the control easier. It also makes it easier to have a faster transient response of the PFC stage, even though its always going to be relatively slow.
 

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To my knowledge, boost PFCs are almost never operated in DCM at high load. You'll get faster loop response, but at the cost of higher input ripple current. Usually loop response isn't an issue for ACMC, even in CCM.
 
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To my knowledge, boost PFCs are almost never operated in DCM at high load. You'll get faster loop response, but at the cost of higher input ripple current.
Thanks, for a 150W PFC stage, with input = 230VAC, output = 400V, L=450uH, F(sw) = 100kHz, then its pretty much in DCM all the time, and the peak current is only about 2.1A. This is very manageable as you know.
In fact, i attach the inductor current waveform herewith.

LED drivers, specially decorative ones, often switch on and off at full load. This obviously causes deviation in the output voltage of the PFC stage, and the PFC output voltage deviation can be made less (without needing a bigger PFC output capacitor) IF your transient response is slightly quicker.

Another point is that almost all the offtheshelf PFC inductors are at the lower Henryic value range, (below 450uH),..this often means DCM operation, but can sometimes be worth it to benefit from the offtheshelf inductor…specially if your volumes are small and your company’s ERP system simply cannot handle another custom wound component, with all the background logistical operation and communication that custom wound components inevitably involve.
The following two offtheshelf PFC chokes are typical of what’s on offer offtheshelf. As you can see, they are relatively low Henryic values..

PQ core PFC inductor by we-online.com (330uH)
http://katalog.we-online.de/pbs/datasheet/760806302.pdf

Coilcraft PFC inductor: (450uH)
https://www.coilcraft.com/pdfs/c1061.pdf
 

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KlausST

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Hi,

I'm no expert with PFC..
This obviously causes deviation in the output voltage of the PFC stage, and the PFC output voltage deviation can be made less (without needing a bigger PFC output capacitor) IF your transient response is slightly quicker.
But as far as I understand PFC on wants the duty cycle of the PFC stage about constant over the whole halfwave of the mains input.
This causes a input current (low pass filtered) hat equal about input voltage in waveform.
This is like a resistive load at the mains input.

If you make the response faster, then the filtered current doesn't follow the input waveform anymore. The cause is:
* non resistive bahaviour
* phase shift between mains voltage and current
* overtones of mains frequency in current

You are correct: the voltage ripple at the capacitor will be reduced.
The faster you make the response of the PFC, the more you get the behaviour of an non_PFC SMPS.

Klaus
 
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mtwieg

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Thanks, for a 150W PFC stage, with input = 230VAC, output = 400V, L=450uH, F(sw) = 100kHz, then its pretty much in DCM all the time, and the peak current is only about 2.1A. This is very manageable as you know.
In fact, i attach the inductor current waveform herewith.
It should be manageable, given the right input filter. Better performance could likely be had by using a higher inductance (with lower Isat), or higher fsw, and operating in BCM. But probably not a big issue here.

LED drivers, specially decorative ones, often switch on and off at full load. This obviously causes deviation in the output voltage of the PFC stage, and the PFC output voltage deviation can be made less (without needing a bigger PFC output capacitor) IF your transient response is slightly quicker.
As KlausST mentioned above, the bandwidth of the voltage control loop is strongly related to the PF you can achieve, especially at heavy load. The higher the bandwidth, the more the Vo ripple will contaminate your input current waveform with second harmonics. This is typically the bottleneck on the loop bandwidth, rather than the transfer function of the converter itself (assuming your fsw isn't very low).

Another point is that almost all the offtheshelf PFC inductors are at the lower Henryic value range
Not sure what you mean by a "PFC inductor." There's nothing special about the PFC application.
 
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