UCC28050: PFC - 600W and 1200W

Hello Kevin,
After looking at the REF-Design of UCC28070, can you tell me, why the GND of bridge-diode is different than the GND of Circuit? I do not see any connection between them? Am I missing anything?
According to Datasheet, CS pin needs positive voltage of 3V to initiate CURRECT-LIMIT (pulse by pulse).

Is there any specific reason that, all high-power PFC [ above 500W] (UCC28063, UCC28180) needs negative voltage of CS pin? I prefer to use positive signal to use ONE-SOLID-GND for everything. Is there any benefit?
Thanks
Shahriar

Hello Shahriar,
Which reference design for the UCC28070 do you refer to ?
If you specify the reference design number then I can look at the schematic and help.
The UCC28070 does not have a CS pin.

The UCC28063 and UCC28180 detect a negative inductor current with respect to system ground because it makes it very easy to use an inverting amplifier in the application. You can see that all of the applications are very straightforward.There is only one connection to this sense resistor. Why do you want to use a positive current sense ?

Regards
John

Hello John,

REF-Design to UCC28070 is : www.ti.com/.../slua479b.pdf
Pin#8 and 9 ( CSA and CSB) are current sensors pins ( am I correct)? I tried to attach the file, but it did not work for some reason. if You send me an E-mail, I can send you more detail information

Power Supply has 3 main blocks of 1200W PFC, 1200W PWM_DC-DC converter and 40W internal power Supply to cover signalling, communication and internal supply. My concern is specially the 40W supply will effect the PFC current sensing, if the GND is same as PFC. It can bias the PFC sense resistor. (Load of PFC might change (5% to 100%), but the 40W is always ON and loaded.

Hello Shahriar,
The GND of the bridge rectifier is tied to pins 4,5 of J1 in Fig 9.
The schematic in Fig 8 shows that pin 4 is tied to GND node.
Admittedly these schematics are confusing. They use two different symbols for GND and they do not show that both nodes are tied together.
You are correct that CSA and CSB are the inputs from the current sense transformer. This is not a current limit though . It is a current sense.
3V on CSA,CSB is about the peak of the linear range for the CSA,CSB sense amplifiers.
On your other question, you should design the pfc so that it also needs to operate for your 40W power supply. Therefore it needs to sense this current also and correct the power factor associated with the 40W load.
The pfc circuit has to operate for the full current drawn from the input.
Hope this helps.
Regards
John

Hello,

How can I get the below information related to UCC28050 and UCC28070.

1) Quotation based on Qty=10K and 50K

2) Eval board ,   Qty=1 or each 

3) Lead -time

Thanks

Shahriar