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We made a 3 phase (3x230v RMS) power supply using TNY264 and FQD2N90 mosfet (to overcome high voltage on the switch).
You can find the schematic and normal condition signals in the attachment in the attachment.
We produced 6 PCBs and they were under test (1x230 v RMS input and 100mA load) during the past 18 months. Now I found out that two of them failed working properly.
The first one was not working at all. When we replaced its TNY264 with a new one, it started working normally. All the temperatures and signals are ok.
The second one was working normally for a while but its temperature was rising and as soon as it exceeded 85 degree centigrade it stop working (probably internal thermal shutdown) replacing its TNY264 with a new one, it started working normally. All the temperatures and signals are ok.
Please let me know your idea about the failure and its reason.