• State Resolved
  • Locked Locked
  • Replies 7 replies
  • Answers 3 answers
  • Subscribers 63 subscribers
  • Views 434 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

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.

UCC28063: ZCD noise at 265Vac

ROBERTO VOLPINI
Prodigy 130 points
Part Number: UCC28063

Hello,

I'm working with the demo board UCC28063EVM-723, where I havee replaced the inductors form factor, from toroid to PQ26/20 core, with step-gap to emulate the L Vs. I curve, therefore the indutor has 430uH @0A and 350uH @6A, the Np/Ns=7.8.

When the AC input voltage rise above 260V, so the rectified peak voltage is next to the VDC, and therefore the positive voltage across the inductor become the lowest, even the voltage on Ns become too low the assure the proper zero current detecting and the mosfet is turned on even the current does not reached zero.

 I have changed the ZCD resistor down to 10k but the problem still remain.

How I can solve this problem? it is possible to pull-up the ZCD pins to the ref voltage by a few hundred kilo ohm resistor?

The schematic I'm using is exactly the same of the demoboard.

Using i nuovi induttori e mosfet STF18N60M2 the efficiency now is changed from 91% to 95% at 90VAC, the inductor temperature are lower by 20-30°C comparing to the original inductors and the mosfet pratically can works without heatsink.

I'm looking forward for your response.

BR/Roberto Volpini  

 

  • 0
    TI__Genius 9790 points

    Hi, Reberto

    Thanks for your interest in TI here. I've contacted the appropriate product group. You should hear from them soon.

    BR,

    Yunsheng

  • 0
    TI__Genius 9140 points

    hello Roberto:

    the issue is because there is no enough offset votlage between PFC output voltage and the input retified votlage.

    The best way to solve it is to increase the PFC output voltage, for example from 385VDC to 405VDC.

    Also by adding an offset votlage through adding a few hundred kilo ohm resistor between ZCD and Vref pin also help here,but may not be enough for you to solve the issue. You can try 220kohm that I did before and proved to be useful.

    thanks.

    BR

    wenbin huang

  • 0 in reply to David Huang33
    Prodigy 130 points

    Dear Wenbin,

    thanks for your reply.

    As expected, by increasing the voltage the phenomenon is attenuated, but it does not disappear.
    By increasing the output voltage of the PFC by 4% to 265VAC (first plot), then the voltage goes from 390V to 405V, the phenomenon is no longer observed, but it reappears at 270VAC (second plot), but this is acceptable.

    Obviously it would be preferable to have a greater current capacity on the ZCD pin (for example 5mA instead of 3mA) so as to allow greater dynamics.

    I take this opportunity to ask you for suggestions on how to improve the dynamic response of the PFC, because it is currently inadequate, in fact, as you can see in the third plot, the output voltage has a drop of about 100V, when the power supplied by the PFC goes from 0 to 300W, how can I to do?

    For clarity these are the colors of the signal traces:
    Green: output current per second of the DC-DC connected to the PFC (0 to 290W)
    Purple: PFC output voltage
    Light blue: voltage across the inductor (channel A)
    Blue: current in the inductor (channel A)
    I look forward to reading your comments
    Roberto

  • 0 in reply to ROBERTO VOLPINI
    TI__Genius 9140 points

    Hi Roberto:

    sorry I can not see the waveform you listed.

    does the dynamic performance still an issue for you?

    for the dynamic performance, the only way is to optimize the Voltage loop compensation.

    You can follow the datasheet or the calculator to find the correct parameter to speed up the voltage loop to help the dynamic performance.

    thanks.

    Wenbin Huang

  • 0 in reply to David Huang33
    Prodigy 130 points

    Dear Wenbin,

    there must be a problem loading the images in the text box because I entered it (using Paste from Word command), is there an address where I can send the plots to you by email?

    About the dynamic perofmances I'm not complete satisfied, I have changed the network compensation to: C15=220pF; C12=680nF; R18=27k (references referred to the EVM-723 300W), although it has now improved.

    About the ZCD issues above 260Vac mains, I have changed the VOUT from 390V to 405V, changing R12, the problem still remanin but above 265VAC.

    Any others sugestions?

    BR/Roberto

  • 0 in reply to ROBERTO VOLPINI
    TI__Genius 9140 points

    Hi Roberto:

    thanks for your feedback.

    you can send the waveform to me through: wenbin-huang@ti.com

    Let us discuss more through email.

    Yes as I suggest to  increase the PFC bus voltage to help the high line issue.

    Please note that you always have the opportunity to let PFC bus voltage equal to peak voltage of ac main line input voltage, at this condition, there is no voltage difference for PFC inductor, so controller miss ZCD detecting.

    we do have some external circuit help at this condition, but keep in mind, we can improve it but there is no way to avoid it.

  • 0 in reply to David Huang33
    Prodigy 130 points

    Dear David,

    we'll continue through email, so we can close this post, thanks for your support.

    BR/Roberto