TNY178 design reliability issues

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I have reliability issues with a TNY178 based design. After 2 years the chip did blow away. The traces on the PCB show that there was a lot of heat around the primary side diode connected to the D pin of the chip. In my design there is an additional series resistor to this diode which also did blow away.

 

What are your ideas to increase reliability, reduce heat in that path ?

Could you please post your schematic,  your PCB and  your transformer design documents?  If you used PI expert to design your transformer please post the PI expert files.  

I can start by taking a look  to  your design  

 

 

Here is a part of the schematic. I do not have the complete schematic, I have to generate it from the PCB. The diode in the board is 1N4007. 

The root cause for the damage seems to be the resistor (the value of 100 Ohm is just a guess). The PCB is burnt arround this resistor. In the datasheet of TNY178 I can see a samle schematic showing different group of P6KE150A + 1KOhm paralell to 100Ohm + 10nF capacitor, but the recommended circuit layout shows the P6KE150A + resistor + capacitor all in paralell. The area is not marked as heat critical, but in my case there was heat there. So, what is the recommended solution for this pin D primary side components ?

Use a fast or ultra fast rectifier diode. Diode 1N4007 is too slow.

If you are not an experienced power supply designer,  it is recommended you design your transformer using PI Expert.   The  problem may be the diode because  it is very slow diode but may happen something else is wrong with the transformer design or somewhere else.

I am especially interested in the network between this diode and V+. The root cause for the damage was most likely that the 100 Ohm resistor couldn't sustain the current and burnt away. After that the TNY178 chip did blow away as well as the voltage became to high with the open transformer. There is no rating in the datasheet about the sustainable power of the parts. I know 1N4007 could sustain 1A. Anyone has some details of the expected current if the TNY178 opens the D pin.(I know that this depends on the transformer, lets imagine an average type). What I am also interested to know if there is need for a second diode paralell to the 10nF capacitor like P6KE150A.

Use a fast or ultra fast rectifier diode. Diode 1N4007 is too slow.

If you are not an experienced power supply designer,  it is recommended you design your transformer using PI Expert.   The  problem may be the diode because  it is very slow diode but may happen something else is wrong with the transformer design or somewhere else.