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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?

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.


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

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


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.


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.