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

[Flyback]

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.

 

[ronsimpson]

Flyback PFC on 400-800Hz

What? 400-800hz? Is the power line 800hz? Switching at 800hz?

 

[AnalogKid]

do you know why nobody does a dual interleaved flyback controller IC with a typical common emitter opto coupler connection?

Yes. Because that is a *very* complex way to get 100 W. Power Integrations can do it in a single chip, a standard forward converter would be slightly more complex and lower noise, and even SEPIC or Cuk converters would be less work, and they're a pain.

Also, what environment has a 115 Vac 800 Hz power? AFAIR, nothing in the MIL space (704, 1275, 1399) goes that high.

ak

 

[Flyback]

What? 400-800hz? Is the power line 800hz? Switching at 800hz?

the mains frequency is 800Hz
Maybe it only goes up to 800hz for short periods , i dont know.....i think its usually 400hz

 

[ronsimpson]

I have done 400hz aircraft power but never PFC on it.

 

[AnalogKid]

I have. You need fast input rectifiers for the bridge, high ripple current capacitors, and a wider-bandwidth control loop. MIL-STD-704 defines "normal" aircraft power at 400 Hz +/-7 Hz (normal), +/-25 Hz (transient), and up to +80 Hz (abnormal). The variable frequency spec does go up to 800 Hz, but I think that is a carry-over from olden days.

The fixed frequency and variable frequency specs are separate paragraphs, tables, and figures. Are you sure you are in a variable frequency environment? they are relatively rare.

ak

 

[ronsimpson]

400 Hz +/-7 Hz

wider-bandwidth control loop.

PFC error loops are for 50 or 60hz. 55hz is center of range. Speed up the loop by 400/55. Forget 800hz.

 

[AnalogKid]

Not sure what you're trying to say. Yes, a control loop for an 800 Hz input is more difficult to design than one for 60 Hz, but the analog multipliers in the latest gen PFC controller chips should be able to handle it.

ak