LM5023: LM5023 -No load output not stable

Nilesh,

Can you post your schematic and transformer details?

Can you post your waveforms showing the unstable output that you see?

At no-load and light-load, the LM5023 will operate in burst mode due to the upper freq clamp at 130 kHz - so could it actaully be burst mode that you are seeing?

Thanks,
Bernard

Hi Bernard,

Thanks for quick reply.

For schematic Pl refer PMP20785 ref design.

Pl see below NL waveform.

Thanks.

Nilesh Kadam.

Nilesh,

I cannot see the waveforms.

If you want to embed any graphics in your post, you need to switch to "Use rich formatting" by clicking on that link under the text box - that switches from the default plain text editor to the rich text editor. You can then use the insert attachment button to insert saved graphics files.

Regarding PMP20785, this is not released on ti.com yet, but I can access it internally.


Thanks,
Bernard

Nilesh,

What is the input voltage for this waveform?

Can you give some background? Is this result seen on a TI board based on PMP20785? Or did you build your own versino of the design?

I check the internal test report for PMP20785 and there seems to be no problem with no-load regulation. How much output load is required on your board to make the output stable? At what input voltage range is your board unstable at no-load?


Thanks,
Bernard

120V AC rms input voltage.
We have build our board with same design but different size.

Nilesh,

Different size for what?

Can you check the questions above? I.e. how much load is required to get a stable output? Is the output stable at no-load at any input voltage level?

Can you also take a plot showing the VCC, OUT and COMP pins of the LM5023 so we can try to see more clearly what's going on.


Can you post your schemtic and and transformer details so we can see what is different compared to the PMP20785 reference design? Something must be different between the designs to cause this issue.

Thanks,
Bernard