top249yn power supply design
This circuit is 26V 2.1A power supply.This circuit works for 5 minutes then it shutdowns. In the primary side of transformer , I measured 490kHz. Why is it 490kHZ? Where is the problem? Normally, it should be 132khz as default. Also the clamp voltage is 2V. I check the blocking diode and zener diode , also cap and resistance on clamp circuit? What should I do to find problem?
Thanks
Comments
Yes , I also check the all points that you ask. Diode is placed correctly, There is no thermalshutdown. I placed a heat sink for TOP249, and its temperature is normal.
I'm sending layout of the circuit.
Can you try and ground the L pin (you wont have UV/OV features) and see if this behavior is consistent.
Also when you say the chip shuts down, can you monitor the COntrol pin and send me this waveform? Lastly, what is the minimum voltage on the bias winding?
The schematic seems to be correct. Can you pls verify if some component (like the FR106 blocking diode) have been placed backwards? More likely would be that the switch is going into thermal shutdown
Can you monitor the temperature of the tab of the TOPSwitch with a thermocouple? Do you have enough heatsinking for the TOPSwitch? Can you send me a picture of your setup/board?
Also, when it stops switching, does it resume switching after a while? Monitor at what tab temperature it stops switching and at what tab temp is resumes switching again.