Hello! load is constant resistor 6 Ohm or ~ 300W approximately.apart from having too much gain in the 431 ckt, are you running at no load? - 'cos this it what typically happens at no load ...
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…?Yeah for some reason the feedback response is way too fast. Can't even see any significant changes in phase shift which would cause the output to change.
Are you sure you have enough capacitance on the output of the converter, and it has a low enough E
R41 = 220 ohm ( because the input divider R's are so low ) & C26 = 100nF
this gives a major pole where it is supposed to be - and will allow the converter to run ( also transpose the R & C for less RF pickup )
Hello! Sure, here I also attached full schematic (last version) and top/bottom PCB views in .pdf.May we see the PCB layout, please?
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:2 things - is you slope comp working ? if not then this needs to be fixed other wise unstable above 45% phase shift
I tuned RP5 to make offset lower this time (please see first waveform). And I didn't really know what offset I will need so I just put the pot at this pin.you need to be adding about a volt max to this with the slope comp for stable operation above 45% phase shift, so 3.35Vpk after 5uS assuming 100kHz ...
Yes, thank you for this advice, now I will measure only using 4k3.Also do not put your scope probes directly on the pins or the tracks going to the points of interest - instead solder a 4k7 leaded resistor to the point of interest ( 4mm lead max to body of R ) then connect the probe to the other side of the 4k7, again shorten the lead to 10mm or so
this will stop you injecting RFI into the sensitive points with your probes.
I am sorry, not sure that I got what o/p diodes is, can you give schematic designation or сlarify what you mean.p.s. what does the diode o/p voltages look like ?
I can understand that shorting shim inductor could affect the stability of the whole converter but what a point to make a working PSFB that cannot achieve ZVS? There is must be another way to make it stable, am I wrong?If L1 is an input choke to the HVDC caps - short it out for the present - as it will affect the stability of the whole converter.
Can you please be more detailed on that? This is not a complete design but a bench model, so it has some disadvantages indeed. But I am trying my best to make it good so experienced and reasoned opinion will help me a lot in the future. If it won't take too much of your time cold you, please give us examples of mistakes made in my PCB and say why exactly you think that these are mistakes. It will help me improve my further designs and also be helpful for other people here.Also, the layout is a mess
UCC3895 DS p.39 "In peak current mode control the RAMP pin receives the current sense signal, plus the slope compensation ramp, through the 510-Ω resistor RRCS. The 10-kΩ resistor RRB provides approximately 250-mV offset bias. The value of this resistor may be adjusted up or down to alter the point at which the internal no load comparator trips."Can I have your rationale for feeding DC into the ramp pin ? it should really only have a slightly filtered I sig + slope comp
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 but has some oscillations (up to 180V), so I put RC snubber 1nF+220R as you told me. This reduced oscillations. I can took this waveforms if it will be useful.o/p = output
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