Hello Everyone,
I am now designing a unit with the specification below:
Input: minimum 18VDC, nominal 24VDC, maximum 32VDC
Output: minimum 18VDC, nominal 24VDC, maximum 30VDC,
Output current: nominal 10A, peak 15A (longer than 5 seconds)
The topology I use is active clamp forward (low-side) with SR secondary the driver used in secondary is IR1167S.
The switching frequency is 140KHz and the maximum duty cycle is 0.56. I have the problem with the secondary voltage spike which goes higher when load goes higher.
The best transformer I tried is PTS40 because it has large effective area (204mm2) and the winding ratio is 5 to 11.
Lp= 40.1uH, Lpr= 0.14uH
Ls=194.5uH, Lsr=1.28uH
And I tried many things to lower the peak voltage which doesn't work.
Since the main switch on primary can't achieve zvs, I tried adding an extra leakage inductor (2uH) and larger the Rdel which has no influence on the Vds on. I think it is because the secondary is conducting during the dead time.
Do you guys have any idea how to improve the zvs and deceasing the spike on secondary?
Thank you and look forward to your reply.