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UC3843: Pulse width and Vfb

Part Number: UC3843

Hi,

My customer want to confirm how much pulse width "D" varies as Vfb varies. Is there any equation related between the two?

Thank you in advance.

Regards,
May

  • Hi Maynard,

    The pulse width "D" is determined by COMP voltage and ISENSE pin voltage.  

    there is no relative equation between D and Vfb.

    Thanks,

    Teng

  • Hi Teng,

    Customer want to know the relation between comp voltage and D, pulse width. Is there any graph  or equation showing relation between these two?

    Thank you.

    Regards,
    May

  • Hi Maynard,

    There is no graph or equation showing the relationship between COMP and D, it is different for each power applications and specs.

    in below picture, the forward voltage of internal diode is Vfd, so the inverting input of the PWM comparator is (VCOMP - 2*Vfd) / 3,

    when Isense pin voltage V_ISENSE hit the  (VCOMP - 2*Vfd) / 3 , it turns off PWM output.

    regards,

    Teng