UCC28070: UNDER SHOT

Hello Omid,

Thank you for your interest in TI portfolio.
Please share the design spec and the scope shot of the under shot that you have reffered.

Regards,
Sonal

HI Sonal

Thanks for good help 

i attach all used full document for you 

note rc in schematic is change to 20ohm and 4.7nf R gate to 20 ohm after this under shot around 120v if increase load under shot increase

if L change to lower valve under shot very low i think duty set big energy save in inductor and make switching too hard don't let voltage L come down near input after this mosfet turn on 

heat on rc parts to high i add another diode close to mosfet bout no any effect only change rc valve to low resistor and high capacitor help to decease under shot  

4KW PFC.zip 

Hi,

Please share the input voltage and output power ranges.
What is the input and load condition when you see the over and undershoot, does this change if you increase the load and line condition.

Regards,
Sonal

HI SONAL

INPUT 55V OUT  263V CURRENT 2 A IN OUTPUT 

WHEN INCREASE LOAD 

FIRST HAVE UNDERSHOT ON OUT PUT CURRENT 0.5A IF CHANGE CURRENT TO 1A INCREAS UNDERSHOT AFTER THIS CHANGE RC MOSFET TO 20 OHM AND 4.7NF NOW START UNDER SHOT START FROM 1 A OUT PUT CURRENT

  

HI
2A IS OUTPUT CURRENT

Hello Omid

Sonal has asked me to work with you on this problem.

The voltage ringing looks to be due to stray inductance in the switched loop from the MOSFET drain, through its source, to the output capacitor, to the PFC diode cathode and then back to the MOSFET.

Can you send me your PCB layout Gerber files please and I will review it for you. If you don't want to post them here then you can send them directly to me at colingillmor@ti.com     

Have you tried disconnecting one of the two PFC stages - simply removing the MOSFET gate drive and tying the gates to their sources would be ok.

If you do that, then the next stage would be to remove one of the paralleled MOSFETs (by disconnecting its gate drive and tying its gate to its source, Q5.1 for example, and seeing if the circuit works in that condition (at lower power of course)

The above tests would be worthwhile but I think that the main cause of this problem is the layout.

regards
Colin

HI
THANKS FOR YOUR SUPPORT
OK I WILL SEND TO YOUR EMAIL
YES I TRAY WITH ONE STAGE AND ONE MOSFET NOT CHANGE MORE
FIRST PLEASE CHECK MY LAYOUT IF FINED PROBLEM OK IF NOT FINED ANY ON LAYOUT TAKING ABOUT OTHER POINT