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TPS40210: Current sense and Pulses skipped

Ibrahima Kaba
Prodigy 20 points
Part Number: TPS40210

Hello,

I designed a Flyback in discontinious mode (2 output + 1 winding for regulation). 

Vin = 20V to 80V

Lp = 19 uH

Freq = 250kHz.

Load max = 1x 3W + 1x5W + 1 winding for regulation

At light load (2.5W) , from Vin = 35V to 80V. The amplitude of the current (measuring Rsense voltage) is not the same at every switching period (alternating between high and low amplitude). At Vin = 60V even some pulse are skipped.

More the load is High, higher the Vin when this "alternated pulses" happen is high. So at mid load (4.5W), this happen from 60V in stead 35V.

Please, can you help to analyse this kind of behaviour ?

Thanks.

  • 0
    TI__Guru* 78270 points
    Hi Ibrahima,

    Can you share your schematic and the waveforms? We would like to take a review.

    Thanks,
    Youhao Xi, Applications Engineering
  • 0 in reply to Youhao Xi
    TI__Guru* 78270 points
    Hi Ibrahma,

    Can we assume the issue has been resolved? Let me close here and you can always reopen it by following a new post.

    Thanks,
    Youhao
  • 0 in reply to Youhao Xi
    Prodigy 20 points

    Hi Youhao,

    Excuse-me for the late answer. Yes we can assume the issue has been resolved. 

    For the benefit of the forum here are my conclusion : 

    Actually, I discover that the external blanking circuit (EBC) I was using in order to blank the inrush current, longer than the 75ns internal blanking of the TPS40210, was too long/poorly tuned.

    The EBC was affecting the regulation. So I removed it, beacause 75ns turns out to be enough in my application. I notice that no more pulses were skipped within the operational voltage range,  and the flyback works properly.

    Thanks.

    Ibrahima