Defective LOT of TOP250YN

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We have a power supply in our equipment (30V, 2.5A) in which we use a TOP250YN. We have produced the equipment for almost 2 years without problem.

However in this january and february 2016 about 30% of power supplys present a problem. They turn off as if heating up to limiting temperature. After cooling down it turns on again. The temperature measured on TOP surface is only around 40 ºC. The correction for the problem is just changing for a new TOP. The percentage of defcts is too high. It appears to be LOT dependent.

How can we solve this problem??


Can you send me the heatsink assembly pictures of the failed power supply. 

Can you also send Schematics, PIExpert/PIxls files and PCB layout.

Can you also describe the procedure for thermal measurements. Can you also give the details of the IC such as lot code and date code.

I would recommend you to closely observe the heatsink assembly on the power supply to see if the heatsink is detached from the part. 



I am also having the same problem. I have design 24V 6A SMPS, its shut down after few second at 5.5A Load, and again power turns On after a while(cooling down). TOP250YN not heated much (more than 45-50 ºC). But when a fan is attached to cool down the Heat Sink (temp is less than 40 ºC), it will work fine.

After viewing this thread, I can only echo PI-NANO in asking what technique was used to measure the case temperature of the devices in question (thermal camera? thermocouple? infrared non-contact thermometer?). In the case of a thermocouple, it it important to ensure that the thermocouple wire type used matches the characteristics of the meter used in order to get accurate results. If the TOPSwitch is canted with respect to the heat sink so that it loses thermal contact, it could cause thermal shutdown. In this case you should measure a high case temperature, probably 100+ degrees.

Also, please respond with the date and lot code of the devices in question.

This is a somewhat unusual problem, and it appears that two users are having similar issues. In order to proceed any further, I would ask that the two users respond with date and lot codes of TOP250 devices that are exhibiting this problem.

I am attaching the IC image for your reference.

Top250YN128.68 KB

Harish, are you only using this lot of ICs in your construction, or a mixture? Do all the failures come from the lot you showed?
Corat, can you please let me know the date code and lot number for the parts in the supplies that are failing?

At this point we at PI are going to need samples of the defective parts to figure out what is going on. Please contact your local PI office to arrange this.
The part image Harish982 posted is from a part that is 15+ years old. -the TOP250Y is a dead giveaway. Parts newer than ~2004 are labeled YN rather than Y.

Here is a form for submission of defective parts for analysis. Please complete form, scan, and submit to rma at power dot com.

Hi dear i have power supply with top250yn .it burst badly when i swith on the input power 220volts.
I checked all the near by parts n changed capacitors .also rewind the
Transformer .pl suggest me what will be the reply .

Hi Davinder here. I have a problem with top250yn
Power supply .top is burnt when ever i wwitch on the input power .i have checked all helping parts near top.i also rewind the transformer .pl suggest me is it lot problem or any other art can i check pl suggest me pl.

Is this a 100% failure issue? Please check to make sure that the secondary is connected and that the secondary and bias windings are the right polarity with respect to the primary.. Lot and date code numbers on the batch of devices you are using would also be helpful. Judging from some of the earlier submissions on this thread, there may be counterfeit devices in the supply chain.

Even no load condition it gets blasts dangrously..i am working for repairing the poliiarity doesnt matter

Polarity of the transformer matters very much. For a positive output supply, the anode of the output rectifier should go negative when the primary switch is on, same for the bias supply. If for some reason the secondary is open, there will be no place for the stored energy in the primary to discharge, and the stored energy will likely overwhelm the primary snubber. If the snubber for some reason is open, there will be no place for the leakage energy to discharge, so the stored leakage energy will likely break down the internal mosfet of the TOPSwitch.. Doe you have a primary snubber at the drain of the TOPSwitch? What type?
Finally it may be necessary to cautiously bring up the supply by disabling the undervoltage such that the power supply will attempt to start at a very low supply voltage. This way you can monitor the drain voltage and current for signs of misbehavior while slowly turning up the supply voltage. Connecting the line sense pin (L) to source disables the undervoltage lockout function.