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Power Integrations Engineer Power Integrations ModeratorPower supply not starting up and hot clamp TVS
Hi,
This power supply is designed for 12V 2.8A output.
We got the first prototype working but has since change the design of the transformer to comply with safety standards.
The transformer has two layer earth screens that separate the two layers of primary windings and the secondary.
It fails to startup. I have captured the waveforms at the transformer primary and bias winding when Vin is 40V. The waveforms are not looking right.
Vbias is 40V to start with.
The clamp TVS increased by 50 deg C in just a couple of minutes.
Please advise what is wrong with the circuit.
Thank you.
bbmilo
Hi,
Looking at your plots seems like you have a sharp reversal of current (di/dt) which leads to huge drain voltage (~280V). This high voltage is turning on your TVS for ~1us. This can heat up the TVS.I assume the CH1(Yellow) is current. Are you powering under full load? Does the power supply start under no load and behaves normally?
Can you please send me your schematic and rough transformer electrical diagram?
It is hard to believe the transformer shielding is causing it.
rgds
PI-Scotty | 38 posts Posted: Feb 25, 2012 | 23:41 PM In response to Hi, Looking at your plots
Hi Scotty,
I found the cause of the problem! The output winding of the transformer was not soldered at all. What a silly mistake. Thanks!
bbmilo | 36 posts 