Fusible Resistor Burn Issue (TNY-284 Based 13V,0.35A AC-DC Converter)

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We have designed 13V,0.35A SMPS using TNY-284 IC and PI Expert Design Tools. 


Input Voltage Range: 65VAC-300VAC

Output Voltage : 13V

Output Max Current: 350mA

We have tested the design for 30 samples and everything is ok. But sometimes the 10 Ω/3W  fusible resistor burns after switch is turned on. No other components damage and if we replaced the burned fusible resistor with a new one it works again.

We have tried to find the reasons and noted some differences(have to make according to availability of component) between PI expert Design Tools and our design.

Here I have attached the PI Expert suggested design, our schematics and PCB layout and noted differences between them.

So, what can be the reasons behind this problem?



Hi Rizvi,

Thank you very much for choosing Power Integrations.

How many failures have you encountered so far? And at what input voltage is the failure occuring?

Could you please send the PIexpert design file? 




We have made 30 sample Pcs. Almost 50% of them damaged within 1 month testing period. Burned happened when we switched the input ON and OFF at 220 V input voltage. It is amusing that only the 10Ω/3W resistor burns. And after replacing the resistor it works again and burns again in further testing. I have attached the PIexpert design and the difference between our design with PIexpert.


Is there any update?

Based on the design file you sent, there should not be any problem with the fusible resistor. You must make sure though that you are using a "Fusible Resistor". This is different from a normal metal film, silicon or MOF resistors. Make sure to use a wire-wound, flameproof, fusible resistor for RF1.

I would suggest programming the device to work at reduced current limit mode. This would improve your efficiency and temperature performance. You can select this under design options. Further optimization is needed to make the design work when you do this. PIexpert offers suggestions on how you can fix warnings if you get them.


As per your suggestion we have checked our fusible resistor. We found that, it was not wire-wound, flameproof, fusible resistor. Then we replaced the resistor with wire-wound, flameproof, fusible resistor and tested it. It seems the problem has been solved. We are testing on multiple pieces for further checking.

Thanks for your help.


Hey how to select reduced current limit mode. Datasheet says TNY284 does not have any current limit selection. Hence I used a 10uf current selecter for my 5v 0.8A circuit. Is it the right thing to do or 1uf capacitor as selector.

Hi Kiranlaleu,

Only TNY285-TNY290 have progarammable current limit. Using 10uF as the BP capacitor is fine although you can also use 100nF for this location. The current limit will still be the standard current limit for TNY284. 


Greetings of the day,
I am trying to build a 5V, 0.6A power supply and the circuit i got is in attachment.
Please suggest me that is any bugs or change in the circuit?

Hi padmnabh,

Thank you for choosing Power Integrations. If may I request, please kindly raise a new ticket for this one.

Best Regards,

PI-Lupin the Third