Author Topic: Power Factor Correction Stage in Power Supplies  (Read 959 times)

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Offline Inductive loadTopic starter

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Power Factor Correction Stage in Power Supplies
« on: November 14, 2019, 09:34:17 am »
Hi, I am currently studying PFC circuits and there is something that is not clear for me, the output of a boost-PFC stage is usually specified with something like: Vout=400V, Iout=500mA. My question is, does this mean that the RMS of input current of the following stage, let's say a flyback converter, should not exceed 500mA ? this sounds wierd because I am sure RMS current of such converters could surpass this value in many power supply applications. Can any one help me understand this please ?
« Last Edit: November 14, 2019, 10:21:48 am by Inductive load »
 

Offline T3sl4co1l

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Re: Power Factor Correction Stage in Power Supplies
« Reply #1 on: November 14, 2019, 12:42:07 pm »
The output is DC.

RMS is not very meaningful at DC.  You would have to justify why you are using RMS in the first place.

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Offline Inductive loadTopic starter

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Re: Power Factor Correction Stage in Power Supplies
« Reply #2 on: November 14, 2019, 01:08:51 pm »
Thanks for your reply,
Actually I want to connect a PFC stage to a flyback converter, the primary side current of the converter is expressed with the RMS drain current: IdsRMS, and peak drain current : Idspeak.
« Last Edit: November 14, 2019, 01:30:34 pm by Inductive load »
 

Offline NiHaoMike

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Re: Power Factor Correction Stage in Power Supplies
« Reply #3 on: November 14, 2019, 01:31:29 pm »
Vout=400V, Iout=500mA.
Just multiply the two to get 200W, then you just have to make sure the load connected to it does not exceed that.
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Offline Inductive loadTopic starter

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Re: Power Factor Correction Stage in Power Supplies
« Reply #4 on: November 14, 2019, 01:45:19 pm »
Ok thanks I understand, but it is just not clear to me how the transformer transfers 200W max when 400V is applied across its primary inductor and let's say IdsRMS = 2A  passes through it.
 

Offline T3sl4co1l

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Re: Power Factor Correction Stage in Power Supplies
« Reply #5 on: November 14, 2019, 01:47:53 pm »
How are you calculating Ids(rms)?

Tim
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Offline Inductive loadTopic starter

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Re: Power Factor Correction Stage in Power Supplies
« Reply #6 on: November 14, 2019, 02:08:23 pm »
According to application note AN-4146 from "On semiconductor" (eq. 9):
IdsRMS = sqrt(D/3) x Idspeak
D is the duty cycle.

you can see in the design example that they found IdsRMS = 1.73A  (p 14)

link: https://www.onsemi.com/pub/Collateral/AN-4146.pdf.pdf
 

Offline T3sl4co1l

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Re: Power Factor Correction Stage in Power Supplies
« Reply #7 on: November 14, 2019, 02:49:26 pm »
Ah, in the transformer section.

Yes, you need that much RMS current handling, at the AC frequency, in the output transformer.

Tim
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