Check the site of Power Integrations. I used their TOPSwitch products, and they are quite suitable for this job. Everything you need is in that TO220-like or SO-8 like package, even the FET. You only need a few passives to get this working. Almost easier than an LM2576 based Buck 
Our assembly house also managed to buy COTS transformers for these from Premier Magnetics. Maybe they are willing to give/sell you a sample?
Our assembly house also managed to buy COTS transformers for these from Premier Magnetics. Maybe they are willing to give/sell you a sample?
Having a parallel smps (flyback or otherwise) running off the PFC seems like a lot of work - now that I think more about it. It's yet another transformer design (I can't find any suitable cots units) and more compliance work.
What about adding one more winding to the transformer that'll be used for post regulation. My digital logic stuff needs 5V and 3.3V - I could fairly easily run 2 small switchers, each in parallel, deriving power from the main transformer 'extra' winding. Even if the cross regulation on the extra winding is lousy, the post regulation will fix that up. Also, this load won't affect the +/- 40VDC since that's being regulated by the pwm directly.
Now my main transformer looks more like:
primary | auxilliary | +40 | - 40 | extra
where:
primary is 400 VDC pfc input
auxilliary is 10 volt power for pwm
+/- 40 is secondary isolated for audio amps
extra is to run digital logic post regulators.
How's this sound?
What about adding one more winding to the transformer that'll be used for post regulation. My digital logic stuff needs 5V and 3.3V - I could fairly easily run 2 small switchers, each in parallel, deriving power from the main transformer 'extra' winding. Even if the cross regulation on the extra winding is lousy, the post regulation will fix that up. Also, this load won't affect the +/- 40VDC since that's being regulated by the pwm directly.
Now my main transformer looks more like:
primary | auxilliary | +40 | - 40 | extra
where:
primary is 400 VDC pfc input
auxilliary is 10 volt power for pwm
+/- 40 is secondary isolated for audio amps
extra is to run digital logic post regulators.
How's this sound?
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