12V output not coming up in TOP257YN based converter
Hi
I have constructed a 12V@10A power supply using TOP257YN device (schematic attached). The input voltage to this converter is 300Vdc from PFC stage.
The entire design was done with PI Expert software (V8).
Problem: 12V is not coming up. Instead, the control pin on the TOPSwitch is charging and discharging continuously, between about 5.8V and 4.8V.
Observation made:
1. Checked for short circuit on the output - No short
2. Checked for open circuit on the output - all components are properly mounted, with correct value and polarity.
3. Removed the resistor R3 (open) to disable over-voltage trigger). Still output is not coming up.
4. This board is a second iteration, with changes in the layout on the output side of the converter. The first iteration (prototype) is working well and there was no problem in bringing up the 12V output.
5. The transformer that was used on the working board was removed and put on this board, since the design had not changed.
6. The only difference between the first prototype design and this design is the device package (earlier I used TOP257EN, now I used TOP257YN). For both the devices, I did the design in PI Expert and all the component values remained same.
Please advise on What could be the reason for 12V not coming up.
Could layout be a problem? Layout snapshots are also attached.Also please let me know if transformer damage could cause this behaviour.
Thanks and Regards
S.Prashanth
Comments
Hi
I verified that the line sense resistor is connected. I found out the root cause: The primary clamp diode (MURS120) was short. This is because, I had wrongly put MURS120, which is a 200V rated diode instead of putting MURS160 (600V). After replacing with the correct rated diode, the converter is up and running without any more problems.
Thank you.
Regards
S.Prashanth
Glad you found the problem!
Are you sure line sense resistor is hooked in -- usually this is 4meg restor to Vpin.