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400-800Hz 115VAC PFC (100w, 28vout) with dual interleaved flyback (isolated)

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treez

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Hello,
We are thinking of doing an isolated dual interleaved Flyback PFC on 400-800Hz 115VAC input.
Its 28Vout +/-2V at 100W. (so that’s 50W for each of the flybacks of the dual)
We are certain that due to peak charging and poor cross regulation, we will not be able to do the vout regulation by regulating the voltage of a low power (<300mW) bias coil on the primary side….instead an isolated TL431/opto type feedback will be needed.

UCC28064A
https://www.ti.com/lit/ds/symlink/ucc28064a.pdf

…so We are going to have to drop a divider down from the primary side Vcc rail and pour the opto collector out into this, and then the divider point into the VSENSE pin of the UCC28064A.

This is more components than wanted, do you know why nobody does a dual interleaved flyback controller IC with a typical common emitter opto coupler connection?

Both flybacks will dump out into the same 28v output.
 

you can easily pull power off the boost chokes for a pri side aux, and then a xtor reg to make it flat.

- - - Updated - - -

as long as there are no periods where the boost converters are not switching ...
 
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Thanks, we are doing it Flyback, and there was consideration of getting the secondary vout regulation done via a primary side bias coil........but this surely is a bad idea, I am sure you would agree.
Another point for this kind of thing is the problem of distortion at the zero cross, which will be more severe with an 800Hz PFC, since the dead time is relatively a greater proportion of the mains period than for a 50Hz PFC.....we wonder if there are specific chips for 400Hz to 800Hz PFC?
 

At 100W we have done single flyback high PFC design with UC3854 ( an old chip but a good one ) adding a few bits to do the zero xing nicely and using the ave current mode to get 0.99 PF, with corresponding min ripple on the o/p caps - worked first time - we used a pri aux winding and very small switcher to get 15V to the chip and opto from output to reg the Vout - with a delay gate on the gate drive to get resonant flyback - max freq at full power low line - and lower freq's below that - best for EMC ...
 
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Thanks, managing the zero crossings is a good point. I notice the L6564 PFC controller has a facility whereby it deliberately discharges the post bridge filter capacitor near the zero crossings. This improves THD and reduces the dreaded post zero crossing ringing which is sometimes seen on PFC stages.
https://www.st.com/resource/en/datasheet/l6564.pdf
The UCC28064A doesn’t make any mention of this.
 

you need the aux to hold up thru the zero crossings so that you can force the power ckt to switch at higher duty cycle thru the zero xings to force the volts down to zero and up again ... on the rising mains ...
 
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