Timeline for Trying to damp transformer output ringing of Flyback Converter when primary FET turns on
Current License: CC BY-SA 4.0
10 events
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| Jan 26, 2021 at 22:13 | comment | added | ucmikesb | After further investigation it looks like the source of the negative going spike on the secondary is from the turn on spike in the primary. Transformer winding capacitances can cause a little current spike right at the beginning of the current ramp through the primary and this coincides perfectly with the negative going spike on the secondary. The strange thing is that I am using a transformer bobbin that is really two bobbins that clip together so there is good primary to secondary separation which should mean low capacitance. | |
| Jan 25, 2021 at 23:59 | comment | added | DKNguyen | You can use an RC snubber if nothing else works. You can google around with regards for how to size it. Typical method involves observing what the frequency of the ringing is and some paper napkin calculations to estimate what it is in the circuit that you need to dampen and acquire initial values for the components. Then proceed to fiddle with them. Or you can jump straight to the trial and error stage. | |
| Jan 25, 2021 at 23:08 | history | edited | ucmikesb | CC BY-SA 4.0 |
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| Jan 25, 2021 at 22:57 | comment | added | ucmikesb | Thanks for the feedback Kartman, the slower output diode is a good idea to try. This one is an ultrafast. Andy, the full schematic is several pages with lots of unrelated stuff and is proprietary so I can't post it all unfortunately. The power supply part is just an LM5021 into a UCC27322 gate drive into a 900V switching FET with standard TL431 reference feedback into an opto-isolator as seen in LM5021 reference designs. | |
| S Jan 25, 2021 at 22:12 | history | edited | ocrdu | CC BY-SA 4.0 |
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| Jan 25, 2021 at 21:15 | comment | added | Kartman | The choice of diode may be critical. Having the diode turn off too fast might be the cause. Try a diode with slower switching. It’s a common cause of EMC issues. I’ve also seen the use of ferrite beads on leaded diodes to address these issues. Other methods are snubbers across the diode (like you’ve tried) and across the winding. | |
| Jan 25, 2021 at 20:47 | review | Suggested edits | |||
| S Jan 25, 2021 at 22:12 | |||||
| Jan 25, 2021 at 20:37 | comment | added | Andy aka | Show the full schematic not some fractal. | |
| Jan 25, 2021 at 20:26 | review | First posts | |||
| Jan 27, 2021 at 1:15 | |||||
| Jan 25, 2021 at 20:24 | history | asked | ucmikesb | CC BY-SA 4.0 |