All You Need To Know About Power Adapters To Fix Stuff! Part 1.
ฝัง
- เผยแพร่เมื่อ 26 เม.ย. 2024
- LER #262 All you need to know about Switch Mode Power Adapters (Wall Warts) To FIX Stuff!.. PART 1. In this video we learn about the Power Supply Circuit Schematics, HOW THEY WORK and WHAT GOES WRONG! We have four practical REPAIR examples. If you want to learn how to repair power adapters, this video, and part two, are exactly what you were looking for.
CHAPTERS
00:00:00 Introduction
00:02:15 Opening Up The Power Supplies
00:13:04 Danger!! Danger!! High Voltage
00:15:01 The Usual Suspects
00:15:32 Practical Repair #1
00:31:59 Basic SMPS Schematic (Pt 1)
00:38:44 Hot Ground
00:40:18 Basic SMPS Schematic (Pt 2)
00:45:20 How Inductors / Transformers Work
00:52:10 Basic SPMS Schematic (Pt 3)
00:53:03 How Analog PWM Works
00:59:35 Basic SMPS Schematic (Pt 4)
01:09:04 Common Faults
01:16:26 Feedback Without Opto-Isolator
01:23:19 Practical Repair #2
01:54:52 Practical Repair #3
02:02:42 Testing the PSU Under Load
02:06:04 Practical Repair #4
02:14:25 Epilogue
The ALL YOU NEED TO KNOW Series
Resistors
• All You Need To Know A...
Capacitors
• All You Need To Know A...
Inductors
• All You Need To Know A...
Diodes
• All You Need To Know A...
Zener Diodes
• All You Need To Know A...
Transistors
• All You Need To Know A...
ATX PSU
• All You Need To Know A...
Amplifiers
• All You Need To Know A...
MOSFETs
• All You Need To Know A...
Thermal Cameras
• All You Need To Know A...
Power Adapters
Part 1: • All You Need To Know A...
Part 2: • All You Need To Know A...
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OSCILLOSCOPES
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SOLDERING
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THERMAL CAMERA
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EEPROM Programming
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CONSUMABLES
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DESOLDER BRAID (I use size 8045)
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MECHANIC HX-T100 Solder 63:37 (I use 0.6mm)
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Richard
Best explanation on power supplies ever watched. Thanks Richard
This video was exceptional Richard. I learned so much. Thank you for putting these together
I found that the cleanest and safest way to crack those power supplies open is to use a vise, and not just to hold them. The force is controlled and applied along a longer area. The case tends to split cleanly and makes it easy to glue back together; plus, less risk of damaging the circuit and get a shock, contrary to the screwdriver method... ;)
Yes, I have had good success with a big vise slowly turned.
First of all let me say thank you Richard for publishing some of the best (introductory) electronics content on youtube, I really enjoy your videos! So please keep up the great work, you really have incredible teaching skills! Seeing section 1 "opening up the power adapters" I decided to share an alternative, less destructive approach that you may or may not know yet: You can use a small syringe equipped with a fine hollow tip and fill it with petrol (lighter pertrol usually works). Use the syringe to dispense the petrol into the seam around the power adapter (all sides) and then let it rest on a kitchen towel for 10 - 15 minutes. Take a hammer with plastic heads (hard plastic not the rubbery ones) and hit the adapter firmly 2-3 times on all sides (no screwdriver, just the hammer). See if the adapter opens up, already. Depending on the size of the seam and how much glue was used in production you may need to repeat the process 2-3 times. The upside of this method: Usally the adapters open up then without scratches or chipping, and if you apply some glue when you put them together after repair they'll look like they've never been opened. The downside of course is, it is considerably slower than your method.
Stumbled across your videos one night scrolling through TH-cam. And I just have to say, there simple but brilliant and informative, keep on doing what you doing.. thanks
Yes! I fixed my radio with almost no previous experience because of this Great Brits’ tutorials.!!
Thank you Richard for teaching me all I need to know about fixing power supplies! Don't waste your time. Don't stab your hand with the screwdriver. THROW THEM AWAY! You are the best!
Bloody he'll got to 1:12 and I've just about understood what you have been talking about I've stopped the vid to have a cup of tea, to allow the flow of information to settle into my brains memory chip. Thank you for the time you take in explaining this to me.......
Just watched through the whole lot and I find your logic impeccable and your insight most welcome. You're managing to even show the old boys how to do it and do it better.
My God that is absolutely the best explanation showing the current path that I have ever seen!
I have my own lab and business doing metrology work and component level board repair full time. I specialize in test equipment and metrology related stuff.
So I’ve always got a pretty decent idea of what’s going on but I’ve never seen it so well explained.
Everyone draws schematics but never actually shows how the current travels in each cycle and half cycle. Visual learning is PRICELESS!
Something I wish more folks like “big Clive” and “diode gone wild” would do also sometimes. They always draw very nice schematics with great! But would love to visually see the current path like you showed here
And its not encrypted in Chinese
A Luthier and a Meteorologist. That's a lot of right side left side cooperation going on there. If I even try to tie my shoes while listening to the TV, it is potential disaster for anyone within 5 feet radius. haha.
Try Donkey learning, I find him very good too 👍
Don't forget Mister EEVBlog. The young man from Australia.
EURICA! After watching your & other soldering repair videos it has finally dawned on me how important it is to first add leaded solder to the soldered parts to make it easier to remove the part is because leaded solder has a lower melt point than lead-free solder. I was a NASA Certified Solder in the 1970s. Years later the industry mandated that lead-free solder must be used and I did not learn the importance of adding leaded solder to a circuit board to change the melting point of the joint to be unsoldered.
For the second power supply MC Hammer says it best. Hammer time.
these videos are insane... the All You Need To Know series is the best i have seen so far
Thank You - this series in particular takes a lot of time and hard work to make!
[ABSOLUTELY LOVE WATCHING YOUR VIDEOS, ESPECIALLY WHEN YOU DRAW THE CIRCUIT AND EXPLAIN HOW THE CURRENT FLOWS 👍🏼🇦🇺.]
This is the first video I have watched by this fellow and he is impressively thorough. I am going to try and finally learn basic electronics and repair from his video playlist, something I have been intending to do for ohhh... bout' thirty years now.
Very comprehensive tutorial Richard thank you for taking the time to do real world repairs
never been nithing on electronics, no one were im at can fix my adio power amp, you professor have taught me how to fix it. Now i want more , never knew i would dig this electronic stuff ! your a genius Professor !!! thank you
Mr. Richard, a humble and warm thank you from across the pond. Graduated Avionics Electronics back in 91. Needed a rust mitigator session and I found the one person I trust to get me descaled. Thank you very much for the video.
Saved both parts of this one to my play list because 90% of electronics is power supply's, so knowing this stuff will be most of the important parts of electronics you will learn...
👍🇮🇪💚🙏🏻⚡️⚡️🔋🔌
RIchard :) Hello mate! :-) A tip for you to try for the difficult ones: 'PUT IN THE FREEZER' for 30 mins immediately before your excellent screwdriver technique. Makes the plastic a little more brittle, and responsive to the sharp 'tap of the hammer' feel free to sdhare this tip. thanks as always. Rob.
Sounds like a good idea Rob, thanks. Oh... I just realised I don't have a fridge/freezer at the workshop. But I could ask the cafe next door to put them in theirs 🤣🤣🤣
Upside down air can can cool down an area quite fast. I sometimes get good results with adjustable pliers, just grab the device above the weld line and squeeze and often it cracks loose. In rarer cases, I just grab a classic razor blade with some pliers, heat it up on the stove until it's red hot then quickly press the blade on the edge near that weld, and it will make a cut, and then you can insert a flathead screwdriver and use it like a crowbar and break the seal.
@@LearnElectronicsRepair ahhh.. you got me there! 😂😂. In my rapid and stupid face saving attempt at defence," you should have a peltier lying around" 🤣🤣🤣🤣.
I proved my own rules. There's two types of genius. The ones commenting advice over the internet with absolutely no clue (me), and then there's others that are not total idiots. watching part two now....
Great learning video! I cut slots in those wall wart cases to let some air flow through.
Thank you once again for the education.
I have to emphasize, again, if you can handle it, the videos can't be too long. We, the viewers can stop the video and pick it up another time. So, just keep it up and thank you, thank you, thank you!
Måns
Thanks Richard for reigning my interest in electronics, you just cost me £50 for a scope on ebay! Just to improve my knowledge skill and fun. Using a scope to diagnose would be handy right now
Richard in answer to your wire tie question 1958. The inventor Marcus Logan who worked for Thomas and Betts.This was an electrical company. The brand name at the time was ty rap. The initial use was I believe in aircraft wiring harnesses.
The correct way to use the ties is to cut the tail flush with ratchet so you don't leave any sharp edges.
The province is according to google. The observation is mine. Good word my friend please keep up the good work.
Thank you so much. The video is very informative and helpful being a novice in electronics. I would like to learn more and see other of your videos. I appreciate the effort and taking time to create this tutorial. More power !
If you enjoted this one just wait for part 2 when we go a little more indepth with power adapter repair - the 'icing on the cake' coming very soon 😉
Great information in the video. Thanks.
Super interesting subject. As usual very well explained. Thanks for the time you take for these videos because we all know that it takes a lot of time. The way you do them is top, with very good drawings. It's quite rare to find such a quality on TH-cam, thanks for that.
Richard, I'd like to thank you for the incredible amount of work you put into your videos. You take the time to explain everything (right down to why you need every resistor). This is incredibly helpful. I've learnt so much watching your videos. Please keep them coming, you have no idea how much these are appreciated.
I must thank you for the excellent way you have explained this as for the first time I now understand what is happening as I’ve seen other videos but yours is the best for making none all ready knowledgeable interested people like myself understand. Thanks 👍👍
I guess a big problem with smaller wall wart's is that for safety they need to be fully enclosed without ventilation which is also really handy for slow cooking electrolytic cap's and other parts as well. Good built in obsolescence too! Its a win win. 😉
Excellent video. Thanks for the considerable time and effort. 👍👍👍
Hi Richard, now we have to convince AvE to send you a Proper Thor hammer 😁. I've also seen people opening these using the force of a Vice.
For noobs - don't forget that these adapters work with 220V / 110V and if you mess up, it can kill you or kill a device you connect it to.
It's great that you never gloss over the real world difficulties - a lot of people would have editted down separating those two boards.
Very true, because if I didn't then no one would learn what they really need to know - it doesn't always go to plan!! 😁
@@LearnElectronicsRepair Well I learned how to open psu's caveman style. You butchered those cases man. 😁😆
Excellent, Richard! Will be waiting to pounce on part 2! Interested in seeing your upcoming video on isolation transformers. I bought one for my bench a couple years ago and had to modify it right out of the box to be truly isolated. Something probably worth touching on in your video that not all come 100% isolated.
Thank you so much for being kind enough to share all of your knowledge with me. I just subscribed and I am beginning this video after I was about 45 minutes into part 2. I enjoy learning how stuff works. Knowing how things work really simplifies the process of figuring out why something isn't working when it wont. God has blessed you with an incredible mind and a kind soul.
God bless you take care.
Great explanation showing the current path love it.
I find that sawing a slot in line with the joint at a corner with a hacksaw allows me to lever the case open with a flat blade screwdriver, this minimises damage to internal components and makes reassembly easy.
Great job Richard, be watching the part 2 in this series.. 🤙🏼🇦🇺
I've found using a vise to compress along the glue joint (without completly crushing it, LOL!) will often break the seal well enough to open it fairly easily.
Try putting the power supply in a vice and gently squeezing the glued sides apart. Works for me and usually the low voltage primary electrolytic are the culprits. Rarely ,the chopper transistor or FET on these fully enclosed ‘capacitor ovens’. Love your channel, I’m still learning after 50 years in the electronics trade!.
I learned lots of stuff looking at your video thanks a bunch. And a bit from me . Paint solvent on the seems dissolves the glue that keeps the case together
your the best, you make this work so much fun I have learned so much from your explanations getting right to the point making it easy to understand. Thank you so much for including the most common faults. It helps make sense of it all.
Holy smokes, the knuckle hair is epic.
Excellent info here Richard, in fact just fixed an LCD monitor wall wart with a bulged output capacitor, doing exactly what you describe at around 1:10:00 - Switch on, screen blinks on and blinks off, rinse and repeat for 5 or so minutes until the screen eventually comes to life. Next switch on gives the same symptoms.
Output cap should be 25V 680 uF, measured only 84 uF.
Thanks for your great channel, haven't seen many other engineers so easily able to break things down, so that it just 'clicks' for beginners.
You are gifted.
Thank you for your kind words. Much appreciated. I have no qualifications or experience in teaching, but when I did my full time City & Guilds in Electronic Repair back in the 80s I had a great teacher and I'm just copying the way he taught us. 😉
This mic volume is much better than recent past videos .. audio was low on several past ones before this one
Absolutely fantastic video 👍
Please Note:
In the Common Faults chapter starting 01:09:04 I somehow forgot to mention the most *common* fault of all - BAD OUTPUT CAPACITORS. I went on to prove this to be the cause of the fault in 75% of the faulty power supplies and will correct this omission in Part 2
Thank you Richard! This is indeed a MASTERCLASS in its own right and you are an awesome teacher. Thank you very much for taking the time to create such a wonderful video and please keep up the excellent content!
Simple yet elegant, yea.
I come from Mr. Carlson's Lab and find your videos really instructive. (Just kidding.) Regards from Portugal. 😀
Thank you for taking the time to do this video! I'm a beginner and am working on an adapter right now and this has helped me a lot.
Thanks Richard, I'm really glad I found your channel! This is a really awesome learning aid. Much appreciated!
Sound is Great!
Hello and greetings. Thank you dear Richard for your fascinating videos involved with lots of tiny useful details. I truly loved the bridge rectifier explanation and the whole paper explanation parts of the video.
I have found your channel just yesterday and I am amazed and excited by the amount of knowledge I might learn from you.
Lots of respect and energy😍
Really enjoying watching the videos, Richard. Very interesting to see how someone else approaches the SMPS repair. There is a book by Jestine Yong from a few years ago about SMPS repair which would accompany this video quite well.
Superb! The best SMPS explanation ever... :)
Thank you
Now try part 2 😀th-cam.com/video/MlDqQpM-VFE/w-d-xo.html
so happy I found your channel. Keep it up sir!, I live for this
thank you Professor Sir !
Great video and audio quality is way better now 👍
Very good explanation of how these work. I like the waterwheel analogy, I’ve not heard that one before. I’ve thrown lots of these PSUs in the recycling - I never thought of taking them apart, and using them in other projects, duh!
Cable ties were invented by Thomas & Betts, an electrical company, in 1958 under the brand name Ty-Rap. Initially they were designed for airplane wire harnesses.
Ty-Rap cable tie inventor, Maurus C. Logan, worked for Thomas & Betts and finished his career with the company as Vice President of Research
That was a tremendously clear explanation of the SMPS principle. I'm going to have another go at fixing a VCR that has so far defeated me. It's not got a PWM chip though, it oscillates using discrete components, which makes it lot harder for me (hobbyist with no electronics training) to understand. Thanks!
Really the discrete PWM controller is the saw tooth oscillator, feedback voltage and op-amp just like I showed here, hopefully that will help you understand it. Good luck with your repair.
As these supplies are mostly glued, I'm using a vice to gently squeeze them along the glue line. If that not helps, I gently hammer it with the flat, pointed side of a household hammer along the glue line. By both methods, you normally hear the glue cracking and the halves coming apart. I never use a screwdriver due to mostly excessive damage to the case and probably the pcb.
Another comprehensive video Richard. Great balance between detailed learning and hands-on practical repair.
I know that you've gone over some of these topics several times now, although in slightly different ways, but we really do appreciate it as it's only increasing peoples understanding (like mine) :D.
This channel really lives up to it's name.
Btw; the mic quality is much better now. You no longer get any background buzz.
Cheers Gauntlet
Yeah I have done some of these topics few times like you say. Sometimes though it is a case that someone sees that a few times and thinks, yeah OK, and the one time more with a slightly different flavour and it is like OMG I got it! I'm still working on the audio, I will happily stick with this mic as all the comments have been positive but I have another combo to try on the next video (tomorrow) just to see if it is better
very enjoyable lesson ...ive learned much...Thank you
Fantastic description, just excellent.
The sound quality is much better. I never managed to watch your old videos on my telephone because of the sound quality. I watched them on my computer. You could also use audio compression. Sorin does this with a cheap microphone and lots of background sounds and the result is pretty impressive.
Actually I found the sound a bit 'tinny' on this one - Part 2 I'm using my Cardiod mic but with the boom stand and cable from this mic. Then we can see for sure which is the best. Others please let me know too. I will play around with audio compression once I decide which mic to use.
Sorins audio is pretty decent but mr Carlson’s labs is another level epic 😁
I hope I am not late but Jayztwocents had some nice videos on audio quality like this one: th-cam.com/video/kXwjXkr_kNc/w-d-xo.html. I totally agree that audio quality is very very important for TH-cam but the story and the way the person speaks and the passion he shows is also critical. Richard is so passionate and entertaining when he speaks that some quirks in the audio are totally fine. Thank you for the great content!
Very good video mate.
Why do TL494 chips pop small crack
On pin 12 you covered a similar chip in your video SMD chip. this one is, off a lab supply I've ordered new one off aliexpress
But the pin out is very similar to what you showed, made me think when you said 10uf cap goes
Good video great leaning keep cracking them open lol very good way of showing the operation of the optocoupler operation 👍 thank you. watched it all
Its great you have taken the time to show and explain your videos are great many thanks
Your explanation of PWM / OP amp / opto isolater in this was fantastic and has helped me understand it far more than some other videos specifically about them!
I assume that these can be picked up and plonked into a circuit within other items to give certain voltages rather than just as a bespoke power supply?
Amazing ,very informative
😮I use some petrol(lighter fluid) applied on connecting parts with a q-tip to dissolve the glue which holds the power supply case together. Give it some time to work and you don't damage the case (dents, holes, broken plastic) Give it a try!
@ 1:38:17 ... Cable Ties were Invented by Thomas & Betts in 1956;... realest under the Brand name Ty-Raps in 1958
Opening when there are no screws: I use a bench vice to squeez the plastic box from all sides and it will crack apart along the seems. Industry standard for sealing the cause is by ultrasonic welding or glues.
Your the main man!
i actually made a good income fixing simple fault on laptop chargers. i also developed a very nice and polished "art" on opening the cases like a nutshell. first by gently hammering the sides but later i just bought a small bice and press them until it pop open very cleanly.
Several people have mentioned this. I have a small vice so I will give it a go 🙂
Heya, no I don't fall a sleep I watched this in 1 sitting it's to interesting to me. I even would like to see your hole shop set-up asspesily the repair part of corse
Great Video and very well explained best on youtube
44:25 - It _is_ a transistor: _Metal Oxide Semiconductor Field Effect_ Transistor
Thanks for the vid !
Hi mate, can you do a video on cleaning a rotor select multimeter, i was getting strange readings which got better the more i redialed in the measurement i wanted on the meter. i pulled it apart and the arc contacts on the pcb for the dial switching were dirty, cotton buds and vinegar... lo and behold, perfect measurements!!... i had forgotton that i had to do this on a different meter 20 years ago... thanks, love your videos.
2hrs Wow Thanks for Great Videos
Thank you - This one took about 3 days to produce (I was working hard on it in between other 'paying' jobs), and in the end was only part 1/ Part 2 will go a little more in-depth and build on everything I tried to teach in this one. After that you should be able to tackle just about any power adapter repair.
Part 2 coming very soon, I already started work on it. Nice to see you enjoyed this one. 🙂
excellent video Richard. I did notice on the power supplies with the faulty output capacitors that the circuit board looked scorched around the output diode. My question is, if the capacitor is bad will it cause the output diode to overheat?maybe you could answer this question in your next video
I think, though this is a little bit of supposition and intuition as I never heard anyone explain why this happens, that the reason the output diode gets hot when the capacitor is bad is something to do with the inductor between the (usually two) output capacitors effectively generating back emf when the diode switches off (goes from forward biased to reverse biased). This 'pulse' would normally just be smoothed out by the capacitor(s) but ends up going back through the diode. There is a very short time when the diode has not yet stopped conducting when it becomes reverse biased - this is why you get special fast switching and schottky diodes - and that is my best guess as to why it heats up.
You get a similar effect in CPU VRMs on motherboards with bad capacitors - the motherboard may work with varying degrees of stability but the inductors get hot. This effect leads some beginners, and not quite so beginners, to believe they have faulty inductor(s)
@@LearnElectronicsRepair thank you Richard for your detailed explanation, I really appreciate you sharing your knowledge.
just thinking about what you said if the capacitor is very near the inductor and diode in such a confined space and these components get hot then this would also heat up the cap which would explain the Cascade failure of the capacitor
Looking forward to your next video
great job
Another great video - love ya hammer! LOL
Richard, this video was very timely for a problem I am trying to troubleshoot with a dimmable LED driver. Raising the dimmer's brightness level over a certain level (about 50%) the driver starts to 'chirp' on/off as you described in this video causing me to say"Ah hah!". BUT! I could not figure out how the effects of a dimmer might change which component is most likely to be the faulty one. Can you provide a few hints for finding the likely faulty component(s) in this case? (Another LED lamp on the same circuit works fine so its not the dimmer control.) I would really appreciate any hints you could point me towards.
Richard always watching your excellent channel, could you please revert back to using a red cursor pointer as I have an issue seeing it. I asked you to change before which you did. Thanks a lot Dave H
Thank you 🙂
Excellent
To open the power supply casing use acetone applying it on the joint leave 10min or so. I'm impatient then try open it with a metal spludger or paint scraper.
So wow trow the hammer you really get into it thumbs up M8
Hi. Thank you for the very detailed explanation. It will help a lot for the beginners like me in that area of knowledge. I have some remarks - if you use some kind of stand to hold the boards while you working will be more easy for you to work and more easy for the views to see what are you doing. Now you go off camera very often. You are using a lot of other tools except the multimeter km601 and this may confuse the beginners that they should have all of them. Well of course the multimeter is sometimes not enough, but exactly for this video you didn't need other tool specially for capacitors. The km601 can measure them - it is the next option just after the diode mode. The tool for checking elements is also helpful and you can check the capacitors also there. I don't know exactly your model what is capable of, but any such tool even the cheep once can do that. And last about how to open the power supplies. You may use a rubber hammer hitting the boxes over the connected edges and then use just a metal or even plastic tool to open them. this way you can keep the box intact. Of course the hitting strength should be controlled. The idea is to break the bond between the edges and not the box itself. If that doesn't help you can try heating the edges with hot air and use a plastic tool to open. Of course you should be carful with the temperature. And only if those two technics doesn't help then continue with those that you have showed.
Hi Ivan
Yes my multimeter can read capacitance but the other capacitance meter is far better at doing it and it cost about €15 so I prefer to use it. I covered this topic on my KM600 review, if you would like to watch that.
th-cam.com/video/fp8U11Cye6E/w-d-xo.html
But in all honestly use whatever you like to take the measurement it still amounts to the same thing. What the KM600 can not do is measure ESR and for some repairs that pretty much essential.
Thanks!
I was confused at the start of it all slowly started getting it as you went along I liked how you did the diagram using the water system for explaining how the current flows I thought that was the best way how to put it I would love to know how every component works on a circuit board its so interesting to learn I'm keen to learn about electronics so beginners classes here I come. Thanking you for an absolutely great tutorial.
have you tried the squeeze in a vice method of opening? I find it's often less destructive.
This video tied so much together. Can't believe I fully understand a PWM and how transformers work mostly from this single video. Great work!
I would like to see an in depth video on ground though. I never heard of hot ground and that makes me a little worried that I missed an important concept somewhere along the way
Very Nice Video
yay enjoyed that
Thank you
2+ hours long and every minute beneficial. I don't know what happens in our modern clown world where the youngsters can choose their gender etc but in the old days new techs would fight to get an apprentice job at the best companies. Listening to Richard is like landing the best mentor at the best appy job. Well Done Rich.
If a youngster or hobbyist watches this channel and cannot get to grips with electronics it might be time to move onto another career. No need to waste money on university when you have these videos to work through.
Hi, I’m not sure if you mention it later but can you demonstrate how to test for charge in a capacitor and how to safely discharge it.
That’ll teach me, patience and all will be answered 🤓
Yeah, I did show that in the first practical repair chapter as you discovered - but I'll show it again more prominently in part 2.
Maybe I missed it, but not once did I hear the words "flyback conveter" during the description of the circuit. These wall warts are invariably flyback converters.
The thing being called a "transformer" does not function as a transformer for delivery of energy from the input ("primary") side to the output ("secondary") side. It is an inductor with a charging winding and a discharging winding. They windings do not conduct simultaneously. If the phasing dots were shown on the schematic this would be more obvious. Energy is stored in the inductor during the time the switch is ON. When the switch turns OFF the energy stored in the inductor is delivered to the output capacitors and the load. There _is_ some transformer action. If there are multiple secondaries (and this includes the winding to power the control circuit) there is transformer action among them where the voltages more or less track according to the turns ratio. The secondary voltage also "reflects" back to the primary winding and "stacks on top" of the voltage of the input supply rail. That's why the switch is invariably rated at a voltage very substantially greater than the input supply voltage. Negligible energy is returned to the primary side but the voltage is present.
A flyback converter delivers "energy packets," one per switching cycle. The duty cycle must change not only for correction of the output voltage due to minor losses or for change in the input voltage, but also and in fact mostly for changes in load current. This is very different from other common topologies used in AC mains powered converters where load current has little influence on duty cycle required except at low currents when the output filter inductor fully discharges each cycle.