• State TI Thinks Resolved
  • Locked Locked
  • Replies 4 replies
  • Answers 1 answer
  • Subscribers 63 subscribers
  • Views 2798 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

Original question:

UCC28180: ucc2810 6kw PFC Debugging to assist

UCC28180: UCC28180 PFC waveform issue

user5010576
Prodigy 80 points
Part Number: UCC28180

I used UCC28180 for PFC. There is a distortion at the beginning of one cycle.The waveform as below:

And my circuit as below:

How can I adjust the parameter around UCC28180 to sove this issue?!

Thanks!

  • 0
    TI__Mastermind 25570 points

    Hllo Xiaohong

    Please confirm the switching frequency - the schematic shows a 100k resistor at FREQ and this would program a very low switching frequency.

    You should also add the clamp diode shown in the datasheet Typical Application Schematic at the ISENSE pin. This prevents the inrush current at startup generating an excessive negative voltage on the ISENSE pin. This is not the cause of the cross over distortion but is important to ensure long term reliability of your design

    The 100 Ohm gate drive resistor is probably too large and this will slow down the turn on and turn-off of the power switch. Slow turn-on will decrease the maximum duty cycle available and this can cause problems such as distortion at the zero crossings.

    The 0.0015 Ohm current sense resistor is a low value - what is the output power of the PFC stage and what is the input voltage range?

    With such a low resistor it is very important to make sure that the connections to the resistor do not add any stray resistance - have you checked that the actual resistance as seen by the current sensing network is 0.0015 ohms. Check this by putting a known current from the source of the power switch to the negative terminal of the bridge diode. Then measure the voltage from the GND pin of the UCC28180 to Pin 3 of the UCC28180. Double check this by verifying that there is no voltage lost across R115.

    Regards

    Colin

  • 0 in reply to Colin Gillmor
    Prodigy 80 points

    Hi Colin

           Thanks for your reply!

            I have added the clamp diode,but if i run a higher power,the pfc function will be abnormal.I think the voltage of ISENSE pin have been limited.The diode is L1SS355T1G.

            So can the diode be cancelled?

            

  • 0 in reply to user5010576
    Prodigy 80 points
    The output power is 6000W. And the operation voltage range is 187V~254V.
  • 0 in reply to user5010576
    TI__Mastermind 25570 points

    Hello Xiahong

    Do not remove the diode - it is necessary to prevent the ISENSE pin being over stressed by the voltage across the current sense resistor caused by the inrush current. If you remove it then you can expect the controller to be damaged.

    The UCC28180 can certainly be used at 6kW but you need to make sure that the current sense resistor is the one suggested by the Excel calculator for this device. I put your power levels into the calculator and it is giving 2mOhm for the Rcs. Please note that the UCC28180 scales its internal amplifiers as a function of the line voltage and you need to set the input voltage range in the calculator to be 85V to 254V - even though you use it only down to 185V. You are using a 15mOhm resistor so the CS signal amplitude will be too large and this will lead to distortion in the waveforms. Here is a link to the calculator which I have filled in your power level - please review it. 2mOhms is a very small resistance and you need to be careful with the connections that you make to it to avoid errors.

    /cfs-file/__key/communityserver-discussions-components-files/196/Copy-of-sluc506.xls

    Regards
    Colin