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  1. P

    PSFB output voltage stabilization issue

    I set Vout to 350V. What is the source of RFI in my converter? MOSFETs? Should i increase turn-on time?
  2. P

    PSFB output voltage stabilization issue

    It’s seems that 220nF at the totem poles gave a significant improvement. First of all, noisy sound is completely gone (or become almost indistinguishable) from 200 up to 700W range even with a 100nF C26 and converter regulating the output. But still at load lvl around 315W and below strange...
  3. P

    PSFB output voltage stabilization issue

    I am sorry for delayed answer. When I was messing around with feedback loop QC somehow popped. There was really unstable situation accompanied with loud crackle and then QC MOSFET just gone. I don’t really know how it could possibly happen since my CS pin is connected to the CST… Maybe Tx could...
  4. P

    PSFB output voltage stabilization issue

    So, the best I could find for now is TLP785 YE which CTR ranges from 50 up to 150%. I have also decreased R22 2.2k down to 1k to even more reduce gain (btw, is it a valid way...?). With C26 at 330 nF I could finally make it stabile under a certain (300-350W) load. But if I decrease load to...
  5. P

    PSFB output voltage stabilization issue

    Now it is clear, thanks. Output rectifiers diodes is D21 and D22 it is ultrafast soft recovery diode 80EBU02, you can find them on pcb using this disignator. Due to the construction feature the cathode pin of it is connected to the PCB via thick wire. The waveform on these diodes looks common...
  6. P

    PSFB output voltage stabilization issue

    Ok, thank you for your help. I will go to my local radio store and buy proper optocoupler to eliminate this gain problem. There is SFH615A-2 in stock, but I thik it is too much gain too so I will try to find SFH615A-1. I am sorry, not sure that I got what o/p diodes is, can you give schematic...
  7. P

    PSFB output voltage stabilization issue

    I think my slope compensation should be fine since I used UCC3895 DS to build slope compensation circuitry and calculate all values. Here are my calculations: On PCB I used 1k resistors instead 3.3k to make slope compensation even larger, with sufficient margin, so it must not be problem with...
  8. P

    PSFB output voltage stabilization issue

    So, I have changed schematic according to your advices: changed R41 = 220 Ohm put C34=2.2 uF put a 4.7 uF at SS pin (C21). (Didn’t placed 1k there because converter will not startup) put C22 = 1 nF and finally, I have added 10nF at pin 9 and 10 to GND. The bad news is that nothing really...
  9. P

    PSFB output voltage stabilization issue

    Hello, mtwieg! The output capacitance is quite high and ESR is low. There is 6 capacitors 1000uF each at the output right after 14,5 uH inductor. Can it be too much capacitance…? I am at a loss to say: is this is the way how not properly compensated TL431 / optocoupler feedback system works? Or...
  10. P

    PSFB output voltage stabilization issue

    Hello! load is constant resistor 6 Ohm or ~ 300W approximately.
  11. P

    PSFB output voltage stabilization issue

    Hello everyone! I got some issues with PSFB output voltage stabilization. I used UCC3895 datasheet as reference for moderator action: removed link to external file server. The problem occurs when converter starts to stabilize output voltage. The output voltage is somehow stable, but...
  12. P

    [SOLVED] PSFB current sensing

    Thank you so much for your helping, guys! I could make my converter stabilaze primary current now (by adjusting voltage at R21). Next thing I will increase bus voltage and will try to stabilize output voltage by connecting feedback loop back and will check ZVS condition. I wonder what is the...
  13. P

    [SOLVED] PSFB current sensing

    Yes, you are totaly right. This is my ommition. I measured it again, as a normal person (using spring) and got а satisfactory result. Thank you! The pink signal is voltage across Tx primary. I have too low prmary current (<1A) to achive ZVS now, so it's predictable results. My purpose was to...
  14. P

    [SOLVED] PSFB current sensing

    Found mistake, CT was wired backwards, just as mtwieg said. Here are new waveforms (red is Tx voltage, yellow – voltage on C62). Now it looks more like the truth, but I still have some doubt this form is the correct one. Signal is too noisy at turn-on. Is it how it supposed to be or still...
  15. P

    [SOLVED] PSFB current sensing

    Hello again, cupoftea! I am just really touched with you care! Thank you so much for these awesome simulations you prepared for me! You can be sure this stuff will help me a lot! A am agreed with you at 100% that «get a representative simulation working before going to the bench». My bad, I am...
  16. P

    [SOLVED] PSFB current sensing

    Yes, im sorry, if i didn't make it clear. QA and QD have no phase shift (diagonal pair). Tx exposed by maximum duty cycle - D clamp.
  17. P

    [SOLVED] PSFB current sensing

    Hello, mtwieg. Strange, It is seems fine to me. CT swings positive first and negative then. Am I wrong?
  18. P

    [SOLVED] PSFB current sensing

    Yes, please see my picture in previous post. For any coil, volt*seconds ON = volt.seconds OFF and this mean that areas under the curve must be equal. As I have a dead time 500 ns, I must provide a sufficient amplitude of voltage on the secondary of my CT during this 500ns reset time (to make V*s...
  19. P

    [SOLVED] PSFB current sensing

    If I understood you correctly, as I remove 20K resistor I am not limiting the reset voltage anymore? So if the problem is saturation this idea should work for me. Reset voltage will develop at stray capacitance of CT and if my diode is the tough one, it should survive it. Am I got you right? CT...
  20. P

    [SOLVED] PSFB current sensing

    Shure, I have sized main transformer properly, it has ETD54 core with equivalent crossection area of 280 mm^2 and 25 turns in primary side. It sized to work fine at much higher voltages that I am testing right now. The CT is a discrete one. I harvested it from some junk PCB. I opened it and...

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