Common moide choke current rating
Common moide choke current rating
(OP)
I am writing regarding the common mode choke in smps EMC filter at mains input.
I need a common mode choke of 14.4mH and 2A.
However , i cannot find one which has this high current for this inductance. (at least not one which is of a reasonable size)
This datasheet is typical...
http://www.farnell.com/datasheets/126975.pdf
..the current is never high enough....i wonder if the current quoted in datasheets is common mode or differential mode?
Also, my SMPS is a 35W offline flyback (Flyback PFC [NCP1651] + Flyback PWM [NCP1337])
The avaerage current drawn form the 240V mains is some 400mA...however, the peak is 1.9Amps....therefore i need the common mode choke to handle this 1.9A without saturating.
Since common mode chokes employ "field cancellation", i am surprised that their current capabilities are almost everywhere quoted at such low values.
I would massively apreciate your assistance or thoughts in this matter.
I need a common mode choke of 14.4mH and 2A.
However , i cannot find one which has this high current for this inductance. (at least not one which is of a reasonable size)
This datasheet is typical...
http://www.farnell.com/datasheets/126975.pdf
..the current is never high enough....i wonder if the current quoted in datasheets is common mode or differential mode?
Also, my SMPS is a 35W offline flyback (Flyback PFC [NCP1651] + Flyback PWM [NCP1337])
The avaerage current drawn form the 240V mains is some 400mA...however, the peak is 1.9Amps....therefore i need the common mode choke to handle this 1.9A without saturating.
Since common mode chokes employ "field cancellation", i am surprised that their current capabilities are almost everywhere quoted at such low values.
I would massively apreciate your assistance or thoughts in this matter.





RE: Common moide choke current rating
http://www.micrometals.com/index.html
RE: Common moide choke current rating
Nevertheless 1,9 peak current for 35 W is quite poor (unfortunately you do not state the input voltage range). Add a small differential mode choke to reduce peak (and RMS) current.
RE: Common moide choke current rating
Checkout Coilcraft and J. W. Miller.
http://www.coilcraft.com/
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RE: Common moide choke current rating
RE: Common moide choke current rating
thankyou all for getting back.
I apologise my rms input current is actually 0.271 Amps...(which would have a peak of 400mA if it was sinusoidal)
I have rigged up the NCP1651 in discontinuous mode, and to keep losses down, i set it up for a longer secondary conduction time.....which unfortunatley gives the 1.9A peak primary current which is drawn from the 240V mains via the EMC filter.
I am not using any capacitance after the bridge rectifier as i want it to be nice half sines there. I have seen some app notes putting capacitance there, though i am keen to avoid it.
RE: Common moide choke current rating
The common mode choke laughs at the peak current. If, and you really have to check that, your RMS current is below the winding's thermal rating, which it seems to be, then your peak current is OK.
The common mode choke is what its name says: Common Mode. That means that you can run any current through it as long as you take the same current back again in the other winding. It will not saturate as long as the two windings carry same, but opposite currents. Think bifilar winding.
Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Common moide choke current rating
-This means 2*line frequency ripple on the output voltage.
-operating thr Flyback only for a few cycles during peak voltage condition --> high stress, poor efficiency.
RE: Common moide choke current rating
Sounds like a boost PFC converter, actually.... Yep, just looked up the datasheet for the part, it's a PFC controller chip.
RE: Common moide choke current rating
- line: 35 W *sqrt(2) /(efficiency *240 V)
- PFC switch: a little twice that value
both much below 1.9 A.
Is the PFC-choke properly rated ?
RE: Common moide choke current rating
Adding Y1/Y2 caps from lines to GND may help further reducing the CM ripple, as most CM chokes I've worked with, show self resonance at freqs. 1 decade below the caps.
RE: Common moide choke current rating
The inductance is important, but you have to look at the characteristic L to frequency. Usually for EMC you need high induct. at 1-50MHz.
You need also a film capacitor after the bridge for the H.F switching current.