TOP258PN - RANDOM FAILURE

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Hello sir/mam,

I have designed one multi-output power supply for printing application.
kindly find an attached schematic.
I did my design and product is in production now.
but I am getting some random failures of PSU from the field.

Problem: one particular ic damaged/burning U3 (TOP258PN) kindly note schematic.
we are doing the burn-in test too before selling.
and getting damaged PSU from field after 2-3 months.
what is the reason getting damaged of one particular ic? and what precautions we have to take in production/design?

첨부 파일Size
PROBLEMETIC_PART.pdf43.06 KB
Full_schemetic.pdf44.4 KB
damaged_psu.jpg127.66 KB

note in 50pcs we got 5pcs damaged. we are only replacing top258pn and again it is working fine.

Hi,

Does anything marginal on the design? How the thermals at worst case ? Do you any waveform showing the VDS of TOP switch. Can you share the design file & transformer datasheet.

Dear sir thanks for responding.
I will provide all the details asap.
I have not soldered D7-p6KE200 clamping diode in all PSUs(note image)
should it affect reliability of SMPS?

1) kindly find waveforms of DRAIN of top switch @ full load
note: top switch working at variable frequency
+5V 2A(main primary with feedback)
+12V 0.3A
-12V 0.3A
+5V 0.5A
2) kindly find the attached image of transformer datasheet.
3) attached zip design file.
4) thermal condition is around 60-65 degree max after 1.5hour loading

TitleSize
xmer_datasheet.jpg905.38 KB
waveforms.jpeg417.5 KB
KRP_MULTI_OP_V1.2.zip5.18 MB

Hi,

Thank you for sharing the data. The Drain to source voltage waveform shows lot of ringing . The Vds stress in steady state is around 620V. Did you verified the stress during line/ load transient conditions. If you notice higher stress, adjust the RCD scrubber values to reduce the VDS stress.
Since thermals are good & low power, I can see only voltage related failure. I cant open the design file on Piexpert online. Please share the .xls file and I will check.

Hi,

Not populating D7 in the clamp makes the supply more vulnerable to line surges . Noticed no MOV at the input too. Both these factors may make the supply really vulnerable to line surge.

thanks a lot for comments, sir.
noted sir, I will work on snubber & MOV
Any suggested MOV part number? the input supply voltage range is (150VAC to 280VAC).
Can I work on transformer primary inductance or turn ratio etc?
sorry sir, I don't have the pi expert file. I sent the PCB file of protel99SE.

Hi ,

Please check below MOV details.

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TDK_MOV.JPG151.58 KB