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Double flyback driver??

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cbfull

Fri Aug 25 2006, 01:48PM

Registered Member #187 Joined: Thu Feb 16 2006, 02:54PM
Location: Central Ohio
Posts: 140

uzzors wrote ...

The old AC ones give better spark length and arcs so I've heard.
Flybacks

The newer ones with the rectifiers chop off half of the AC signal coming from the secondary, and this reduces the overall current. The AC flybacks allow more current and the spark is "hotter" which typically allows it to be drawn to a longer arc once it is struck.

The AC flybacks are the ones to use if you are constructing something like a plasma globe or a multiplier. Rectified (newer) flybacks are great for charging high voltage capacitors. There are other applications for either type but I only use my ACs for plasma globes and for studying inverter circuits.

Hope that helps.

FaLLoUT

Sat Aug 26 2006, 10:04AM

Registered Member #241 Joined: Thu Feb 23 2006, 09:13PM
Location:
Posts: 19

Great i can get like 20 from my uncle next door (he fixes TVs) and he maybe can find me an older one.. well il just use it for sparks and burning things until i am satisfied and then i might concider using it for a plasma globe or some project :)
I guess i can bypass the problem of a new flyback outputting lower voltage by just using 2 new flybacks instead of 1 old AC flyback.. So you say that monitor flybacks are better? in what way are they better? Becase i have a 15" hanging around at my house.. oh by the way my uncle has an old ocilloscope in his yard he can give 2 me can i use the flyback in that for anything cool?

Wolfram

Sat Aug 26 2006, 12:10PM

Registered Member #33 Joined: Sat Feb 04 2006, 01:31PM
Location: Norway
Posts: 971

Newer flybacks are way better for generating large arcs/sparks than the old ones. The old ones don't handle too much voltage before they flash over. Monitor flybacks are weaker than TV flybacks, simply because monitor CRTs require less voltage and current than a big TV. DON'T take the flybacks out of scopes, a scope is a hundred times more valuable than a flyback for an electronics/HV hobbyist. And scope flybacks are usually very small too. Some scopes don't even use flybacks, just voltage multipliers.

FaLLoUT

Sat Aug 26 2006, 12:53PM

Registered Member #241 Joined: Thu Feb 23 2006, 09:13PM
Location:
Posts: 19

The osilloscope is very very old.. it is like from... 1970-80 or something i guess.. Ä°t has been under rain and sunlight for 5 years and it is falling apart so.. i think that would be the best thing to do with it rather than shoot at it with a air gun

Part Scavenger

Sat Aug 26 2006, 05:39PM

Registered Member #79 Joined: Thu Feb 09 2006, 11:35AM
Location: Arkansas
Posts: 673

Here's the deal with flybacks. You'll hear that DC's(modern) are better than AC's(old) and vice versa. Some DC flybacks output wimpy sparks and others don't. Other times it's the driving frequency that makes it have poor performance. That's why you hear of better results on either side. Generally, the bigger the TV/Monitor, the move voltage you can get out of the FBT.

Plasma globes can only be driven with AC current, so you'll need an AC flyback. If you can't get one, you might be able to disable the diodes in a modern flyback but its really hard and the flyback usually dies soon afterward. (see "Flyback Diode" in the archives). You can also pull the core out of a DC flyback and wind your own. (Easier. The center of an AOL CD is the perfect size for the former)

An AC flyback usually looks alot different than a DC, and it usually has a diode about the size of a pencil connected between the tube and the FBT.

You can drive a flyback from any TV, don't worry about model#.

In general, DC flybacks have gotten me higher voltages because the AC ones will arc over. Generally they seem to be more fragile as well. I think if drive an AC FBT unloaded, this will contribute to it's demise. BTW, I've never completely killed a DC flyback.

BTW... Yes, I was using DC flybacks with multipliers. Similar? Not really, but it helps.

With the ZVS driver make sure you have over 10-12V driving or it won't oscillate.

FaLLoUT

Sun Aug 27 2006, 07:54PM

Registered Member #241 Joined: Thu Feb 23 2006, 09:13PM
Location:
Posts: 19

Thanks a lot for the advice. You said like 10-12v driving is minimum what will be maximum? is there a way of roughly
telling what a FBT can take? In other websites they said 26 volts is for old flybacks (well i am not afraid of killing a flyback i have plenty lying about)

Wilson

Sun Aug 27 2006, 10:02PM

Registered Member #78 Joined: Thu Feb 09 2006, 11:27AM
Location: Sydney, Australia
Posts: 133

The maximum Vin is limited by your mosfets/igbt's voltage rating. They see pi*Vin across the DS, and you should add a safety margin to that.

You know when you've reached the max of a flyback when you can boil water on its surface

The interesting thing with flybacks is that the output voltage isn't totally dependant on input voltage- as the output is mainly dependant on high voltage spike which appears when you switch current quickly through the primary. As such, a full bridge running at 30V could produce the same output as a TV driver, in which i believe rectifed mains (or perhaps ~200V) is switched in with 1200V transistors.

Part Scavenger

Sun Aug 27 2006, 11:44PM

Registered Member #79 Joined: Thu Feb 09 2006, 11:35AM
Location: Arkansas
Posts: 673

...or melt skin.

Wilson's right, theorically, there is no limit to Vin on the ZVS driver as long as the driver components can take it. The flyback is the least limiting factor.

...

Mon Aug 28 2006, 01:11AM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445

Just make sure you have enough inductance in the series inductor...

Also, you must realise that the number of primary turns greatly affects the output for a given voltage... Halving the turns is about the same as doubling the input voltage

FaLLoUT

Tue Aug 29 2006, 06:27AM

Registered Member #241 Joined: Thu Feb 23 2006, 09:13PM
Location:
Posts: 19

... wrote ...

Just make sure you have enough inductance in the series inductor...

Also, you must realise that the number of primary turns greatly affects the output for a given voltage... Halving the turns is about the same as doubling the input voltage

So you mean that dropping the number of primary windings means more higher output voltage on a flyback?
-----------------------------
And something else, i see different codes like NE555 on timer IC's. Are all the ones that have "555" do they do the same thing, or does it matter if i use any kind of 555 in a timer?

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