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LM5023: Power management forum

Raj Shahu
Prodigy 80 points
Part Number: LM5023

Hello,

I am testing flyback board controlled by LM5023 and we already tested it multiple times till 30W and it gave expected results.

Now with the same board having same components I am not getting results that i got before. Now at no load I am getting just 8V at load and then the IC seems to stop working(probably due to some protection) and the capacitor starts discharging down from 8V.

Similar behavior happens at light load condition.

I have checked other components on the board, they seems to be fine, Why does the IC stop working, whereas I used to get proper results up-to 30W earlier?

Here is the schematic:

Regards,

Raj 

  • 0
    TI__Mastermind 31130 points

    Hello Raj, 

    Thank you for your interest in the LM5023 flyback controller. 

    The schematic diagram that you provided is a simulation schematic, but I assume that it closely represents that of an actual prototype board. 

    Since your board did operate correctly for some time in the past, I don't believe that there is any design or schematic error. 
    Instead, I believe that some component got damaged during handling of the board.

    With a damaged component, the board no longer completely matches the schematic, and is functioning as it would if one of the components in the schematic was open, shorted, or had a drastically different value.  

    Ceramic capacitors can be cracked open if the board is flexed too much.  Chip resistors can also crack but that is more rare (though not impossible).
    Also, circuit connections may open up, such as a hair-line crack in a copper trace or a component termination broken free of the pad. 

    Please examine your components to see if any can be found that are visibly damaged, or measure the wrong value.  Replace any suspected parts.  
    If none are found, then look for bad connections, being careful not to possibly create more flex-damage.  

    It may not be mechanical, though.  A part may be damaged, or its value drastically changed, by some overstress such as too much current, too high voltage, or too much heat.
    If you find a bad part and replace it, the new part will be subject to the same overstress that damaged the old part, so examine the stresses and mitigate them once the board is working again. 

    Regards,
    Ulrich