Hi,
Check out this Power Supply Design Seminar topic on "Flyback transformer design considerations of efficiency and EMI" : https://ti.com/lit/slup338
On page 17, there is a section on "How to estimate and minimize leakage inductance" with a simplified…
For a lighting application that requires PFC, UCC28811 is recommended. PMP22538 is an example of a 60W PFC-flyback using UCC28811, but output voltage is not exactly what you are asking for.
Hi Vipin,
I think what is happening here is that the UCC28730 is in CC regulation at startup because the converter must supply the 1A load plus current to charge the output caps. This causes the startup time to be longer, and there is not enough capacitance…
For this design, the turn ratio provided on the schematic is correct (looks like the transformer datasheet might have a typo). The ratio is 13.5:1:4(Pri:Sec:Bias), so Npa = 13.5/4 = 3.375, and Nas = 4/1 = 4.
You can use these values for Npa and Nas…
Hi Tuen,
I think maybe synchronous rectifiers Q5 and Q9 are not turning on completely when Vin is above 60V. Can you capture the gate-source voltage waveforms for Q5/Q9 at 48Vin and >60Vin?
-BK
Hi Ernest,
Sorry my delayed response. The PMP7391 design uses output diodes. If the diodes were replaced with synchronous rectifiers and careful redesign 95% should be possible with an active clamp forward.
However, an easier path to a solution might…
