Flyback Understanding journey - Page 1
Forum section: electronics / projects

author: Atom
author_rank: Regular Contributor
timestamp: August 20, 2018, 04:48:12 pm
content: hello to everyone hope you're doing well.so i'm diving into the flyback converter from mains for the first time, i have a lot of salvaged ee ferrite cores that are waiting for me, so i thought that flyback topology would be a good start, i'm going to use something like Viper27 ncp1014 or the tinyswitch3 (tny264 and 279)(already on hand) power range of 10-20w.i've watched this:https://training.ti.com/understanding-basics-flyback-converterDCM discontinuous modeCCM continuos modereally helpful, i would recommend it to everyone that is starting, so here's the first answer... i have to understand in wich mode those chips workstny279 ----only DCM? in all graphs there is the ringing in the dead timencp1014 ----DCM and CCM is mentioned on the datasheet so it switches between the 2viper27/26 -----i don't know helphttps://www.fujielectric.com/products/semiconductor/model/power_supply/technical/fly-back_transformer_design.htmlhttps://www.fujielectric.com/products/semiconductor/model/power_supply/technical/box/pdf/Fly-Back_transformer_Design_Rev_1_0_E.pdfi have found those papers from fuji electric in wich they go through the calc for the transformer, they seem very well made (i haven't read them). i wanted to know in which mode those ics works because the first step into the paper is to know the working mode.if you have other suggestion or similar ics well, i'm all ears...probably i'm going to need help in the other phases of the desing so please help a poor student that wants to know what he's doing and not blindly copying the schematics (i could but i don't want to, PI and ST offer the online calculator with even the schematics and values). those are great tools and i'll use them as reference.the final project would be :220vac insec1 5v 1A 5wsec2 170v 50ma 8.5w -----------~15Wi have a lot of EEcores but i doubt that anything over EE22 would be needed (i have EE19 EE20 EE22 etc), something on the magnetics would be good, cause those are all salvaged cores from stanby rails of pc psuso if you have any guide or link that you think it would help a newbie understand all this please share itany kind of help is greatly appreciated, thanks in advance, all this was written pretty fast and english is not my native language

author: Atom
author_rank: Regular Contributor
timestamp: August 20, 2018, 05:02:26 pm
content: so if there is anyone intrested here's the PI and ST soultions, i thought i had to include those.another question correct me if i'm wrong, the PI software doesn't let me go over 100v for the output maybe because they say that the max open switch time is 65 so the close switch time is 35% now whit an input of 330vdc (220*sqr2)330 : 100% = x : 35%------------x = 35*330 / 100 = 115V max?also why in the st solution they are attaching the aux winding to the 170v dc out winding? is a bug in the software ? or they are powering the chip from the secondary, if select only the 5v 1A output the aux winding seems to be "generated correctly" st solutiuon 2if i use the viper 27 instead of the 26 the aux winding is where it should be.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: August 20, 2018, 07:22:37 pm
content: You may find it's wiser to start small, say with an isolated 12-12 DC-DC converter using UC3843 or the like.The UC384x family is simple enough it can also be built from discrete logic (an op-amp, dual comparator, flip-flop and driver), if you like. (Or about a dozen transistors, if you're really keen on doing it discrete.)Working with high voltages invites obvious safety problems, but also parasitics that you probably aren't expecting, and don't have any understanding of, or experience with. The notable cases being: excess capacitance (winding self-capacitance, and between windings) causing turn-on surge current and common mode noise; and leakage inductance causing potentially destructive peak voltages.Tim

author: Atom
author_rank: Regular Contributor
timestamp: August 21, 2018, 07:09:38 am
content: Hi first of all thanks, secondly do you have any paper that would be useful to me ?Quite some time ago i had a professor that was quite the practical tipe and we wound a ferrite core transformer, while winding we inclined the turns of the primary on and then the second layer (of the primary)we inclined the wind8ngs in the other direction ...so let's say if you watch them with x ray they are always wound in the same direction (how it should be) but they form an X pattern ...he was calling this the bees nest (now i'm traslating from italian)And i remember he mentioned how whinding in this way tbe capacitance ould be reduced ....is that true or i remember incorrectly?Bye

author: Atom
author_rank: Regular Contributor
timestamp: August 21, 2018, 07:11:56 am
content: Quote from: T3sl4co1l on August 20, 2018, 07:22:37 pmI ll look into those thanks.

author: Johnny10
author_rank: Frequent Contributor
timestamp: August 21, 2018, 07:53:37 am
content: I found this pdf useful in understanding Flyback SMPS I was repairing.http://micro.rohm.com/en/techweb/knowledge/acdc/acdc_pwm/acdc_pwm01/940/

author: Atom
author_rank: Regular Contributor
timestamp: August 21, 2018, 09:55:10 pm
content: This is what i was looking forthanks