Need help with AC flyback - Page 1
Forum section: electronics / beginners

author: HeyBen
author_rank: Newbie
timestamp: August 12, 2013, 09:11:55 pm
content: Hello all, been lurking for a while and need help sourcing a flyback without diodes or caps. I am looking at vintage TV flybacks but is there a better source?I am looking for 0-30Vac on the primary to maybe 10kVac on the output and one that can withstand ~200khz. Does anything exist? Should I wind my own? I have flybacks but they have diodes and I can't get them out of the potting.Any help would be appreciated.

author: SeanB
author_rank: Super Contributor
timestamp: August 13, 2013, 05:52:34 pm
content: Go to any old TV spares supplier and look for old LOPT's that need an external tripler, and this will not have internal diodes. You will have to drive it at 15.725kHz and add a resonating capacitor but these are available, and will have an output of around 5kV.If you need other then take an old core and former, a lot of 40 or 48SWG wire and a lot of mylar transformer tape and then wind your own, then vacuum encapsulate it.

author: HeyBen
author_rank: Newbie
timestamp: August 14, 2013, 02:12:17 pm
content: Thank you SeanB. I found some fairly new ones that I am going to attempt to hack, it looks like their diodes are potted but somewhat separated from the main case.I am considering winding my own but need to learn more about them. My research has me thinking that transformer wire is regular wire and not coated. That's what I don't understand, it seems like the electrons would pass through each layer, jumping from wrap to wrap without actually travelling through the wire itself. That makes me confused, it's not like a coated motor winding, or at least that's my understanding of transformers so far.Then there's the air gap, resonance and capacitance that affects the output, it seems over my head.

author: SeanB
author_rank: Super Contributor
timestamp: August 14, 2013, 06:17:16 pm
content: Transformer wire is coated with a thin enamel layer. You will have to look up how to wind a high voltage coil using it though.

author: Paul Price
author_rank: Super Contributor
timestamp: August 14, 2013, 07:52:20 pm
content: I looked and found at least one TV CRT HV flyback xformer on Ebay.com (usa) that was sans diodes and caps. I bet you can find it too!

author: HeyBen
author_rank: Newbie
timestamp: August 15, 2013, 12:51:58 pm
content: Yes, I found one on Ebay for around $60 that was vintage. The day before there were like 5 but someone scooped them up. I actually need 2 so it was cheaper to buy 2 $15 FB and hope rather than pay $120 and pray.Thanks SeanB, I am used to seeing wire coated in red enamel. It didn't make common sense to me, that's why I was confused.

author: HeyBen
author_rank: Newbie
timestamp: August 15, 2013, 04:16:49 pm
content: I am wondering if a toroidal xformer would be better for my needs, but I read that they don't handle HV well and can arc between the layers. Is this true?

author: Paul Price
author_rank: Super Contributor
timestamp: August 15, 2013, 11:28:16 pm
content: yes it's true

author: Paul Price
author_rank: Super Contributor
timestamp: August 15, 2013, 11:39:14 pm
content: Since the HV diodes are a series connected physical construction in a TV flyback, it should be fairly easy to use a drill to remove and destroy the diodes to get to the hi-side of the flyback winding. A Dremmel tool might also be sued to laterally cut a thin slice down trough the diode stack to locate the bottom diode connection going to the transformer HV winding, where you could simply solder a wire to the diode case and either remove one or just leave all the HV rectifier diodes in place.

author: Paul Price
author_rank: Super Contributor
timestamp: August 15, 2013, 11:47:19 pm
content: Right at the top of a search for TV Flyback Transformer.They are offering at least 10 without diodes or caps, brand new, for $16 US each.

author: HeyBen
author_rank: Newbie
timestamp: August 22, 2013, 01:13:54 pm
content: Thanks, but I am not 100% sure they are sans diodes. I bought the Sanyo ones that look very similar but have the shaft, I cut the diodes out yesterday, it was pretty simple. Now to see if it works for me. I think what I really need is a HV pulse transformer.http://www.ebay.com/itm/04-2751-60108-Replacement-For-Sanyo-TV-Flyback-Transformer-275160108-/121034000417?pt=US_TV_Boards_Parts_Components&hash=item1c2e304821

author: Paul Price
author_rank: Super Contributor
timestamp: August 22, 2013, 01:16:34 pm
content: I am 100% sure they are sans diodes.

author: HeyBen
author_rank: Newbie
timestamp: August 23, 2013, 05:09:47 pm
content: Ok thanks for your help, if these don't work I will give one of those a shot.

author: eman12
author_rank: Contributor
timestamp: August 24, 2013, 06:04:55 am
content: Quote from: HeyBen on August 12, 2013, 09:11:55 pmHi there,You surely can find one in very old TV's.I have 2, I managed ro rewind the primary windings very simply to get my desired output as well. The results were very Promising at frequncies of 15kHz, It could give me almost 10KV very easily, Sorry I did not need to cover 200kHz because I did not need to do so, It Depends mainly on the core.Good luck