PFC Power Supply VCC

[rffx]

I am designing a SMPS with a PFC correction circuit and then a 390V to 24 V DC-DC converter. Both the PFC chip and the DC-DC converter chip require a 12v VCC. Any suggestions for a circuit? I was thinking of using a resistor and a cap with a clamp after the diode bridge, but it is about 30 mA and that would be quite a bit of wasted power. Another option would be a flyback converter. Would running this off the Diode Bridge mess with the PFC? Any suggestions?

 

[VEBill]

Searching with the keyword 'bootstrap' (in addition to more obvious terms such as SMPS) brings up plenty of ideas.

TI app note SLYT077:
A better bootstrap/bias supply circuit (PDF)

2005, so perhaps a bit old. But seems to still be valid.

That's just an example. Plenty of others.

 

[VEBill]

An overview:

...SMPS -- START-UP METHODS

 

[VEBill]

Special IC...

Supertex LR745 (PDF)

Appears to be an attractive approach.

Good luck.

 

[rffx]

Thank you VEIBLL! Very good ideas and suggestions. The LR745 looks promising