UCC28063: Connecting both PFC boards in parallel

Hi Mason,

If the loads are separate and the voltage loop for each PFC stage is separate then the setup should work. Do both PFC stages work when Vcc is run from an external power supply?

Regards

Peter

Yes, Both PFC stages work when master's Vcc is run from Auxiliary winding and slave's Vcc is run from an external power supply.

Hi Mason,

So when the slave is not working, where does its Vcc come from? From its own aux winding on the PFC inductor or from aux winding on the master?

Can you check the Vcc voltage levels of the master and slave boards when the circuit is not operating correctly.

Regards

Peter

Hi

Slave is working but cannot limit over current.

I checked CS voltage isn't changed when I pulled over load.

Slave's Vcc comes from aux winding on the master.

Vcc voltage levels of the master and slave are 14V.

thank you. 

Hello Mason,
Unfortunately it is not possible to run the UCC28063 in this configuration.
This is what I think is happening:
Because the inputs share the same supply with bridge rectifier, there is nothing preventing the return current for the slave from returning on the master section (or vice versa). So the master section may trip too soon and the slave section not trip at all.
The sections will not share current properly because of the location of the CS resistor.
If you want to share current properly between two separate pfc sections you should consider using the UCC28070.
This has separate current control loops for each section.

Regards
John

I'm sorry to have bothered you.
Each board has its own bridge rectifier and ac noise filter.
Is it still a problem?

Mason,
Its still not going to work.
Even with separate bridge rectifiers the slave return path can go through the master return diodes.
There is nothing forcing master or slave to use its own bridge rectifier return diodes. It only takes a few mV's of offset for unequal current sharing.
Does this make sense?

Regards
John

Hi John

okay, thank you for your support.