It is worth considering, since the two transformer solution would be more likely to be able to fit into the profile aspect. The pair would be more reliable as well, each doing half the work (or less) than the 'fool bore' solution.
Then don't use a friggin flyback based driver.
I have made 180kV X-Ray supplies that get used at airports and sit inside a lead box full of oil over a cubic foot in size. The series pair method and c-w multipliers is a good choice here.
You must make the current follow the line voltage, else no good PF. This does require a modulation, regardless of whether we call it modulator or give it a different name.
The datasheet link from Codico? Repeating it doesn't make it any more useful. I know how to do PFC. What I need to know is where to get the proper magnetics (without breaking the bank).
Most of all their switching frequency is quite low, and the Rdson fairly high. Big, toasty ...
-- Regards, Joerg http://www.analogconsultants.com/
I wasn't suggesting that you use these chips. I was giving you examples of chips that could perform the pfc function without a modulator, to demonstrate that you don't need one in your application. Virtually any device that produces critical conduction in a flyback can be made to do the same. You don't need a modulator, if you're going to use a flyback circuit for isolated PFC, at 'low' power. You don't need a modulator. You don't need a modulator. You don't need a modulator.......
Never the less, you might find the reading informative. First google search return on LNK405.
First google search return on "LNK405". First google search return on "LNK405". First google search return on "LNK405". First google search return on "LNK405".
DOH!
I read it as 250mms, not mils, as in thousandths of an inch. Yer right. That IS damn small! Nevermind. ;)
nb
-- "Do you recognize me? No! ...cuz I don't work here" Support labelling GMO foods http://www.nongmoproject.org/
:-)
We hired a few British engineers and one of them handed a drawing to the machine shop. A week and almost $900 in cross-charges later they gave him the requested teeny tiny piece and his jaw dropped ... "WHAT?!"
-- Regards, Joerg http://www.analogconsultants.com/
A simple constant frequency discontinuous (or complete energy transfer) flyback will, if completely unmodulated, produce credible power factor corrected input current waveshapes, given an unfiltered rectified AC input voltage. This is easily confirmed by observation, calculation or basic power conversion reference material.
You would have to modulate duty cycle slowly (as in all PFC regulators), in order to roughly regulate the output voltage without introducing harmonic content. multiple input frequency current is passed unaltered to the output filter.
You do not modulate it to obtain PFC. You cannot use a peak input current control method, because it would be counterproductive to the aim of PFC.
For a critical conduction mode circuit (which only differs by it's introduction of FM), it's not as direct a relationship, but the power throughput improvement, improved noise and reduced stress is enough to make the alteration desirable. It is often enough to introduce nonlinearities in the voltage modulator, to correct for the predictable deviation that's introduced.
Critical conduction circuits don't give a damn what the peak current is, though ovbiously switch current may be monitored to provide protection, so long as it doesn't interfere.
RL
And that's what I meant, you do need a modulator to do this because you can't let the output voltage go haywire. I have tried using the regular feedback for this, even on the LT chips, and it causes the PF to turn horrid.
That's how most flyback-PFC chips I looked at work, and they all have a modulator.
In my case there's two criteria: Holding the PF somewhere above 0.9, using the smallest possible core and keeping the output voltage within a
+/-30% band. We will get there, but not with of-the-shelf ferrites.-- Regards, Joerg http://www.analogconsultants.com/
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