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  • TI Thinks Resolved

UC3843A: UC3843A output frequency is different from Oscillator frequency

Prodigy 10 points

Replies: 2

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Part Number: UC3843A

Dear TI

UC3843A is used as flyback, the output voltage is non-isolation, input :11~120VDC

At light load ,increaing input voltage, the output PWM frequency is decreased, less than Oscillator frequency .

for example, the input voltage 60VDC, the PWM frequecy 40KHz ,Oscillator setting frequency is 160KHz, but the output voltage is stable

I want to know why caue this, is the operation mode normal ?

  • Hi

    Can you post some scope plots of the waveforms, Oscillator and gate drive . At light load I think the controller is skipping pulses and then it appears that the switching frequency is less than the oscillator frequency.

    Regards

    Peter

  • In reply to Peter Meaney:

    Hi,

    Its been 6 days since the last post so I will close the post. May be you have solved the issue if please open another post.

    Thanks

    Peter

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