Thanks for the help, everyone. It is really appreciated!
You say you have 3uF on the primary DC bus?
As Xavier already states, 3uF is nowhere near enough.
It's 10uF. Yes, it's too small. I added 820 uF just to try, as I happened to have it at hand. Less ripple but no change at all in the output voltage drop issue.
Will likely use somewhere around 100uF in final solution.
Your sim is now attached and working....you have chose very deep CCM....so maybe look into SiC sec diode. Or just make it more near to DCM
You chose bias winding reg...so will not be that accurate over the load range.
In the sim, you need to add the resistances of caps and L's
As you know, you chose K1=1, so no leakage, that will need adding in but i sure you know this
You also need to pick component type and P/N...not just have the generic diode. I had to change your diodes as i did not have them in mine.
Be sure to choose ultra fsat diodes where needed.
Thanks! Now I have my version working as well, but with one exception, the TI UCC28C54 model is NOT working. It works when I use the LT1243 however.
I noticed you made quite some changes to component values in your version and it seems to work fine at max load, but becomes unstable at lower loads.
It transits from DCM to CCM at about 55% load.
I also added the snubber and adjusted the coupling factor to 0.995.
Now to the interesting part. The simulation shows an output voltage of 10 volts at max load, while in IRL I see 8 volts
Question is how big difference it makes to use the LT1243 in the sim instead of the 28C54. The 28C54 has max Duty cycle = 50% and the switching frequency is half the RT/CT frequency. Though that can be compensated for in the sim to some extent, but might perhaps have effect on slope compensation (which isn't in included here though)
Here's my updated version that now works fine.
However, yours is about 10 times fasteri in simulating. Do you know why that is?
UCC28C54-12V7A.asc (6.19 kB - downloaded 17 times.)
Thanks!