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Old 26th February 2005, 05:35 AM   #1
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Question PFC Switched-Mode Power Supply

Has anyone out there ever tried Active PFC'ing the front end of their Switched-Mode Power Supply?

Brief mentions were made on another Power Supply Design thread (5000W SMPSU), and it was suggested that with the mention of PFC'ing, a new thread should be started.

OK, so, any takers?

Steve
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Old 27th February 2005, 11:06 AM   #2
Alme is offline Alme  Ukraine
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Steve, continuing this topic, here's another combined solution from Fairchild - PFC and converter - all-in-one already synchronized - FAN4803 chip. I tried to attach pdf application note but, unfortunately, it's exceeding maximum attachment size.
I'm in particular interested how to make a PFC for a single SMPS supplied from 3-phase mains, didn't find such information yet. Can anyone share experience about 3-phase power factor corrector principles?
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Old 27th February 2005, 11:12 AM   #3
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here's Fairchild's kilowatts effective PFC solution (just to replace main FET with IGBT).
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Old 27th February 2005, 03:00 PM   #4
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Default Synch'ed PFC and PWM

Alme,

Thanks for the link. I seem to remember Mico-Linear had the same thing a few years back, but they couldn't make it sell. A PFC synchonized to a doudle-ended PWM (Like an SG3525 or MC33025), all in one chip, all with totem-pole outputs. Pretty cool.

As for 3-Phase PFC, I, to would like to see something like this, as I recall, 3-Phase power already has a high power factor (something like 0.8), so PFCing that shoul be rather easy, I think.

OK, after I looked at it, I see that the ZVS is used to reduce losses even further, and improve things a little bit. However, it is NOT a PWM synch'ed to the ZVS PFC.

The chip I was referring to was a constant-frequency PFC, synch'ed to a dual-output PWM, and wasgood for at least a couple of kW.

Steve
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Old 27th February 2005, 03:34 PM   #5
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Steve, do you mean PF=0,8 in the case when 3-phase rectifier of 6 diodes is loaded with capacitor (and other real complex load) ?
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Old 27th February 2005, 04:00 PM   #6
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Default 3-Phase PF

Not too certain. It would seem that if the cap were very big (say, more than 1-2uF), then this would seem to defeat the purpose of the PFC in the first place.

I know that a small cap is used right off the rectifier bridge to remove some of the high-frequency component, but that's it. The 120Hz haversines are what is supposed to be fed into the PFC stage.

Perhaps with a 3-phase (depending on the type- either 120-208V wye or 250V delta) there are three single-phase bridges, each with its own PFC, and then combine the three at the outputs. I'm just guessing here, but I will do a Google search and see if anyone makes a 3-Phase PFC Controller.

The PFC-PWM Chip I referred to in my last post was MicroLinear's ML4826 PFC and dual PWM Controller chip. However, it would seem that MicroLinear has divested itself of its power control line od producxts and is soley on the GHz thing. I was lucky, however to get a schematic and datasheet from their book.

I guess I will have to stick to using ON's MC33262 PFC chip and ON's MC33025 @Mhz doudle-ended PWM chip. I mean, they're not bad, in act, they're both very good chips, but I just would like something with the PFC and the PWM all in one chip, synchronized. The '33262 is critical conduction, not constant frequency.
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Old 27th February 2005, 04:25 PM   #7
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Default 3-Phase PFC

I just did a Google search for 3-Phase PFC, and came up with this link-

http://www.technologydynamicsinc.com/galvanically.php

and it's downloadable into PDF format, too. I read it, and basically, it's like I thought- three 1-Phase PFCs OR'ed together at their outputs. Works with 115V Delta systems. This is peculiar, beacuse I don't know where anyone uses 3Ph Delta at 115V per phase. I do know that in the US, it's either 120/208V wye with neutral, or 240V Delta with no neutral. Hmmmm.....
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Old 28th February 2005, 06:51 AM   #8
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Thanks for the link, Steve. I find this information confirming my ideas about 3-phase PF correction. Still it's not quite clear how they sum DC outputs into single capacitor - this looks somehow strange like connecting voltage sources in parallel.

Seems to me that I already mentioned MC34262 chip in '5000W SMPSU' thread I tried to calculate chokes for 'critical conduction' and 'constant frequency' PFCs and got that choke volume is visibly smaller for fixed frequency operation. The advantage of '34262 is simplicity and not that strict flyback diode requirements; disadvantages are floating EMI spectrum and impossibility to synchronize with other subsystems.

okay, waiting for other guys to join this discussion
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Old 1st March 2005, 02:17 AM   #9
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TI makes a PFC/PWM chip- both syncronized at 1:1 or 1:2 but there is only one PWM output for each stage. I was going to use this chip and another dual ended gate driver chip for a solution in the past. We decided against the PFC, though, so I just went with the SG3525.

PFC/PWM combo controller
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Old 1st March 2005, 02:17 AM   #10
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