Tinyswitch blows up at turn on
I designed a power supply using a Tinyswitch III (TNY276) and it blows up at turn on.
I am using a primary RCD clamp similar to DI-118 in order to limit the maximum peak drain voltage.
Can you help me to resolve this problem?
Roberto Yokomizo
Electronic Engineer
Comments
Hi Tucker,
Yes, I designed the PCB and is similar to EP-91 circuit board.
I made test in two prototype (please see the photo) and the both power supply blow up at turn on.
After that the junction drain-source has a low resistence (20 ohms).
Roberto.
Who built your transformer? Have you double checked the phasing?
Do you know what its primary saturation current is?
Bring the AC input voltage up slowly from 0, and observe the Drain voltage. Stop raising the AC voltage when the peak Drain voltage reaches about 600 V. Show me the waveforms. Preferably include the Drain current by using a high frequency current probe.
Hi Tucker,
The transformer was build by another company in my country.
I sent the transformer specification (designed using the PI Expert program), but the person that assembled the transformer inverted the secundary windings.
Now I am making tests in order to check if all is OK.
Thank you very much for your assistence.
Roberto.
Is the prototype on a PCB? Did you design the PCB yourself?
Pls. post an image of it. Pls. also post the schematic and the specification.