High reflected voltage

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Hi, I make a prototype using the attached design. But the reflected voltage across the RCD clamp is too high (approximately 227V across Capacitor CC) even with a low RC = 33k, with full load (decreases with decreasing load). But design show that it may around 176V. I don't think the leakage inductance is too high. What is the reason for these too much reflected voltage? How can I reduce it?
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ras123, I have reviewed attached design, and according to design sheet the peak drain voltage should be 588.9 volts. The peak calmp voltage is equal to the the peak drain voltage minus the max input voltage which computes to be 214V. You are seeing 227 which is a little higher than that and I suspect it is due to higher leakage inductance. The most Critical part of your transformer design is the 2.8V output winding because it a low voltage higher current output which tends to make effective leakage inductance higher. Measure the leakage inuctance of your transformer by from the primary winding by shorting the 2.8 volt secondary winding. If it is high you will need to improve the coupling of the 2.8V winding to primary. Make sure you are using triple strand construction as called out by desing sheet and that this winding layer completley covers bobbin width. In general we suggest keeping drain voltage below 600 volts. As long your design is below this you should be OK.
Hi, Thanks for the help, but please note that the Vclamp is only 177V as per design. Anyway, Since it may not easy to reduce leakage inductance, any other way to reduce reflected voltage? by changing device or transformer core etc.?