TNY277PN Problem
Hello,
I have a Problem with my power supply design based on a TN277PN.
Please see the attached schematic.
The problem is, that the 15 Ohms resistor (right side) allways blow up after 1-2 seconds after I have switched the circuit on.
When I replace the resistor by a short wire, the TNY277 get very hot and blow up, too.
I have checked my PCB-layout 100 times ;-) and there is no difference between the layout and the schematic. So I am sure there is fault in my circiut.
Can you help me, please?
This is the transformer which I have used:
http://www.myrra.fr/cgi-bin/gamme_74000.asp?Fabricant=Power%20Integrations&switch=TNY266&BySwitch=74014%20%20E16%20%2012w%20%2024/24v&CritereTa…
Best regards,
Matt
Files
| Attachment | 大小 |
|---|---|
| pif.pdf | 12.31 KB |
评论
I believe that the problem is that the output diode you have chosen, the SS23, has far too low a Vrrm. The SS23 has a Vrrm of only 30 V and your output voltage is 24 V which means that the reverse voltage on your secondary winding will be significantly larger than this.
What is likely happening is that the secondary diode is failing which causes the core not to be reset and the flux staircases upwards causing the TinySwitch to fail due to overcurrent.
I would suggest you closely follow AN-23's recommendations and calculations to make sure all parts are properly chosen. Also using PI Expert for your design greatly simplifies the design process as it automatically selects output diodes and many other components. However you will have to get more detailed transformer specifications from your supplier.
Hope this helps! Good luck!
