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UC3842: Noise on RtCt pin

Atul Bhakay1
Prodigy 160 points
Part Number: UC3842

Hi 

I have built a power supply circuit using UC3842 . Input of power supply is 20VDC to 70VDC and

Output : a) 5V/0.3A (GND 1)

b) 24V / 0.2A and 5V / 0.2A  (GND 2)

c) 24V / 0.2A and 5V / 0.2A  (GND 3)

The power supply s functioning satisfactorily on full load throughout the input voltage range

Kindly go thro the RtC pin waveform and advise how to get rid of the noise

  • 0
    TI__Expert 7080 points

    Hello Atul,

    If you capture the RT/CT pin voltage and Main FET Vds in the same waveform, you may find that the noise you mentioned happens at Main FET turn on or turn off point. that is a switching noise and no influence for the controller operation, why you need to get rid of it ?

    Thanks.

  • 0 in reply to Jaden Ning
    Prodigy 160 points

    Hi Jaden Ning,

    Yes, you were 100% correct. The noise is at the point the MOSFET turn on or off.

    Also, as you mentioned, it has no influence on the controller operation. 

    So actually I do not need to get rid of it.

    Thanks once again

    This resolved my issue.