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Lm5180-q1

user5278629
Prodigy 120 points
Part Number: LM5001
Other Parts Discussed in Thread: LM5180, LM5180-Q1,

Tool/software: WEBENCH® Design Tools

Hi All,

I am using Lm5001-q1 IC for design of 2W power supply. I have 4 output windings in which 3 are isolated and 1 is non isolated. I am taking the feedback from the non isolated winding to make it as a non isolated flyback converter.

The input voltage is 12 volts and I am expecting 7 volts across all the secondary windings.

But when the input is connected, I am able to get only 3.4volts at the output winding.

Checked with the transformer and it is fine.

The duty cycle is 20 percent and has saturated.

Can anyone please suggest what moght have gone wrong?

  • 0
    TI__Guru 68495 points

    Sorry I was misled  by the title "LM5180-Q1". Our group covers LM5001 but not LM5180.

    It sounds like you may have mistake in the transformer polarity usage.  Please double check all windings and correct the wrong winding polarity.

    Thanks,

    Youhao Xi, Applications Engineering 

  • 0 in reply to Youhao Xi
    Prodigy 120 points

    Hi,

    Thanks for the response.

    We have checked for the polarity, impedance of windings etc. All are fine.

    At no load we are getting output at isolated windings. But not in the non isolated winding which is taken for the feedback. The output voltage is 3.4volts (7 volts expected) and voltage at the feedback resitor is 0.8 volts.. That means the duty cycle has to increase since the expected voltage across feedback winding is 1.26V.

    But we can see duty cycle is not increasing but remaining constant of 18 percent.

    Is there any issue??

  • 0 in reply to user5278629
    TI__Guru 68495 points

    Hi,

    Please share your schematic.  Also take some waveforms: Vin, Vout, CS and Vds of the MOSFET.

    Thanks,

    Youhao