Flybacks- Big & Small; Performance Analysis
Nikhil, Sat Jan 10 2009, 03:41PMI've been using flybacks with small cores for all my activities. Recently i came across way big flybacks in a local junkyard. Most of em had a huge case and a big core. I suppose the o/p of fbts are at the mercy of internal arcover or melting which has nothing to do with the 'case' size. Why not vary the size of the core alone keeping the case size constant, whats the purpose of a big case? Definitly more energy must be involved with the bigger cores but is'nt this a clash b/w power and insulation!! Do bigger flybacks have better insulation/ higher voltage ratings, r they more reliable than the smaller ones? Could you plz help me understand the difference in performance btwn the big n small flybacks- How does SIZE matter?
Re: Flybacks- Big & Small; Performance Analysis
Dr. Dark Current, Sat Jan 10 2009, 03:55PM
You don't want to use a big transformer in a small TV because the manufacturer would be paying for extra power which would never be used.
Dr. Dark Current, Sat Jan 10 2009, 03:55PM
Nikhil wrote ...
Why not vary the size of the core alone keeping the case size constant, whats the purpose of a big case?
With bigger case you can use thicker wire and more powerful diodes -> less heating.Why not vary the size of the core alone keeping the case size constant, whats the purpose of a big case?
Nikhil wrote ...
So whats the use of a big core when the insulation is inadequate? Could you plz help me understand the difference in performance btwn the big n small flybacks- How does SIZE matter?
The insulation is always adequate, otherwise the transformer could not sustain full voltage. For small power, use a small transformer. For higher power, use a big transformer. Does make sense? So whats the use of a big core when the insulation is inadequate? Could you plz help me understand the difference in performance btwn the big n small flybacks- How does SIZE matter?
You don't want to use a big transformer in a small TV because the manufacturer would be paying for extra power which would never be used.Re: Flybacks- Big & Small; Performance Analysis
Littlew, Sat Jan 10 2009, 04:47PM
Big core - more power.
Big flyback - better insulation than small FBT, bigger diametr of wire - less heating. If you got old style flyback transformer you can use primary coils to draw arcs(approximately 800 turns of 0.20-0.50mm wire), and if you are lucky you can find flyback that produce 25kV AC.
Littlew, Sat Jan 10 2009, 04:47PM
Big core - more power.
Big flyback - better insulation than small FBT, bigger diametr of wire - less heating. If you got old style flyback transformer you can use primary coils to draw arcs(approximately 800 turns of 0.20-0.50mm wire), and if you are lucky you can find flyback that produce 25kV AC.
Re: Flybacks- Big & Small; Performance Analysis
Nikhil, Sun Jan 11 2009, 02:13AM
ok. Regardless the size of the unit, even without overdriving still enormous amts of energy can be pumped thru them. At how much wattages are these devices normally run in CRTs?
Nikhil, Sun Jan 11 2009, 02:13AM
Littlew wrote ...
Big core - more power.
Big flyback - better insulation than small FBT, bigger diametr of wire - less heating.
Big core - more power.
Big flyback - better insulation than small FBT, bigger diametr of wire - less heating.
ok. Regardless the size of the unit, even without overdriving still enormous amts of energy can be pumped thru them. At how much wattages are these devices normally run in CRTs?
Re: Flybacks- Big & Small; Performance Analysis
Littlew, Sun Jan 11 2009, 04:08PM
But you can find TVs where flyback transformer used to power whole TV, so there is 100w or more
Littlew, Sun Jan 11 2009, 04:08PM
Nikhil wrote ...
ok. Regardless the size of the unit, even without overdriving still enormous amts of energy can be pumped thru them. At how much wattages are these devices normally run in CRTs?
In most CRT tvs >20-40W, but it can pump more power.Littlew wrote ...
Big core - more power.
Big flyback - better insulation than small FBT, bigger diametr of wire - less heating.
Big core - more power.
Big flyback - better insulation than small FBT, bigger diametr of wire - less heating.
ok. Regardless the size of the unit, even without overdriving still enormous amts of energy can be pumped thru them. At how much wattages are these devices normally run in CRTs?
But you can find TVs where flyback transformer used to power whole TV, so there is 100w or more
Re: Flybacks- Big & Small; Performance Analysis
Dr. Dark Current, Sun Jan 11 2009, 04:40PM
Surely, they will run at 300W but just for a few minutes before getting extremely hot (there are rare exceptions). Most of them may run at 100W continuously but their lifetime can be much shorter.
Most designers design the parts for reliability, this also means overrating them. If they can just supply the needed power, they might well fail after 2 years, but if designed propery, can operate for e.g. 30 years or more. It's just that some designers (and manufacturers) overrate their parts more and others less or not at all (china).
Dr. Dark Current, Sun Jan 11 2009, 04:40PM
Nikhil wrote ...
ok. Regardless the size of the unit, even without overdriving still enormous amts of energy can be pumped thru them. At how much wattages are these devices normally run in CRTs?
I think its around 50W usually.ok. Regardless the size of the unit, even without overdriving still enormous amts of energy can be pumped thru them. At how much wattages are these devices normally run in CRTs?
Surely, they will run at 300W but just for a few minutes before getting extremely hot (there are rare exceptions). Most of them may run at 100W continuously but their lifetime can be much shorter.
Most designers design the parts for reliability, this also means overrating them. If they can just supply the needed power, they might well fail after 2 years, but if designed propery, can operate for e.g. 30 years or more. It's just that some designers (and manufacturers) overrate their parts more and others less or not at all (china).
Re: Flybacks- Big & Small; Performance Analysis
Kolas, Wed Jan 14 2009, 03:11PM
Hi.
For the most part (as far as my experience goes) the insulation of the larger FBT's is substantially better then the smaller ones. And clearly the larger core can handle more power. It would be interesting to know which is designed to go first, the diodes or the insulation between the secondary sections.
I have had some large flybacks that were capable of producing an estimated 80kV, while others could barely produce 40kv... does anyone know which manufacturer makes the best flybacks for outputting excessive voltages?
Kolas
Kolas, Wed Jan 14 2009, 03:11PM
Hi.
For the most part (as far as my experience goes) the insulation of the larger FBT's is substantially better then the smaller ones. And clearly the larger core can handle more power. It would be interesting to know which is designed to go first, the diodes or the insulation between the secondary sections.
I have had some large flybacks that were capable of producing an estimated 80kV, while others could barely produce 40kv... does anyone know which manufacturer makes the best flybacks for outputting excessive voltages?
Kolas
Re: Flybacks- Big & Small; Performance Analysis
Dr. Dark Current, Wed Jan 14 2009, 04:28PM
I had good experience with Sony Trinitron flybacks, some have a ~5cm plastic "tower" sticking out of the top to which the HV lead is attached. Such as this one, producing god-knows-how-much kV, and it is still perfectly fine by today:
it could do more but I just used halfwave rectification for oh-cool 50hz buzz 
Dr. Dark Current, Wed Jan 14 2009, 04:28PM
Kolas wrote ...
Hi.
For the most part (as far as my experience goes) the insulation of the larger FBT's is substantially better then the smaller ones. And clearly the larger core can handle more power. It would be interesting to know which is designed to go first, the diodes or the insulation between the secondary sections.
I have had some large flybacks that were capable of producing an estimated 80kV, while others could barely produce 40kv... does anyone know which manufacturer makes the best flybacks for outputting excessive voltages?
Kolas
I'm pretty sure the diodes go first. In my experience the core is not the limit, but the heating of the diodes and secondary winding.Hi.
For the most part (as far as my experience goes) the insulation of the larger FBT's is substantially better then the smaller ones. And clearly the larger core can handle more power. It would be interesting to know which is designed to go first, the diodes or the insulation between the secondary sections.
I have had some large flybacks that were capable of producing an estimated 80kV, while others could barely produce 40kv... does anyone know which manufacturer makes the best flybacks for outputting excessive voltages?
Kolas
I had good experience with Sony Trinitron flybacks, some have a ~5cm plastic "tower" sticking out of the top to which the HV lead is attached. Such as this one, producing god-knows-how-much kV, and it is still perfectly fine by today:
it could do more but I just used halfwave rectification for oh-cool 50hz buzz Re: Flybacks- Big & Small; Performance Analysis
Kolas, Wed Jan 14 2009, 04:45PM
haha that looks alot like my work bench. Cool looking flyback though. My best preforming flyback was a similar looking unit but it was white and massive, as is that one.
Kolas, Wed Jan 14 2009, 04:45PM
haha that looks alot like my work bench. Cool looking flyback though. My best preforming flyback was a similar looking unit but it was white and massive, as is that one.
Re: Flybacks- Big & Small; Performance Analysis
GeordieBoy, Wed Jan 14 2009, 04:50PM
> I'm pretty sure the diodes go first...
Also, remember that the stack of series connected diodes in a TV flyback transformer only needs to be rated for slightly more than the DC voltage that it puts on the picture tube's anode. The diodes used in this application ARE NOT required to withstand a reverse voltage of TWICE the DC output voltage like you would find with most normal half-wave rectifiers. Can anyone explain why?
-Richie,
GeordieBoy, Wed Jan 14 2009, 04:50PM
> I'm pretty sure the diodes go first...
Also, remember that the stack of series connected diodes in a TV flyback transformer only needs to be rated for slightly more than the DC voltage that it puts on the picture tube's anode. The diodes used in this application ARE NOT required to withstand a reverse voltage of TWICE the DC output voltage like you would find with most normal half-wave rectifiers. Can anyone explain why?
-Richie,
Re: Flybacks- Big & Small; Performance Analysis
Proud Mary, Wed Jan 14 2009, 04:57PM
HR Diemen - the Spanish manufacturer of after-market LOPT spare parts - publish a vast compendium of data on LOPT's called "The Book" which you can download chapter by chapter from various sites around the web.
"The Book" is generally reckoned to be the Bible of all things LOPT.
Data sheets (but not "The Book") for many hundreds of LOPTs can be downloaded free from the HR Diemen website here:
There is an English language version button marked with a Union Flag:
Proud Mary, Wed Jan 14 2009, 04:57PM
HR Diemen - the Spanish manufacturer of after-market LOPT spare parts - publish a vast compendium of data on LOPT's called "The Book" which you can download chapter by chapter from various sites around the web.
"The Book" is generally reckoned to be the Bible of all things LOPT.
Data sheets (but not "The Book") for many hundreds of LOPTs can be downloaded free from the HR Diemen website here:
There is an English language version button marked with a Union Flag:
Re: Flybacks- Big & Small; Performance Analysis
Dr. Dark Current, Wed Jan 14 2009, 04:58PM
I'm actually running this one in flyback mode, maybe the reason why it still lives...
Dr. Dark Current, Wed Jan 14 2009, 04:58PM
GeordieBoy wrote ...
Also, remember that the stack of series connected diodes in a TV flyback transformer only needs to be rated for slightly more than the DC voltage that it puts on the picture tube's anode. The diodes used in this application ARE NOT required to withstand a reverse voltage of TWICE the DC output voltage like you would find with most normal half-wave rectifiers. Can anyone explain why?
Because the flyback pulse is magnitudes bigger than the forward one...Also, remember that the stack of series connected diodes in a TV flyback transformer only needs to be rated for slightly more than the DC voltage that it puts on the picture tube's anode. The diodes used in this application ARE NOT required to withstand a reverse voltage of TWICE the DC output voltage like you would find with most normal half-wave rectifiers. Can anyone explain why?
I'm actually running this one in flyback mode, maybe the reason why it still lives...
Re: Flybacks- Big & Small; Performance Analysis
GeordieBoy, Wed Jan 14 2009, 05:09PM
> Because the flyback pulse is magnitudes bigger than the forward one...
BINGO - Correct Answer! I thought that if anyone got that right it would be you!
Yes, the voltage waveform in a typical flyback converter is highly asymmetric. That is the forward voltage is relatively low in magnitude and applied for a long time, and the flyback voltage is very high in magnitude and exists for only a short time. The volt x second balance is maintained across all the windings still.
This property is one of the many reasons that the flyback converter is so popular in cheep PSUs and works well in the LOPT stage of TVs. In designs with HV output half-wave rectification can be used whilst minimising the troublesome PIV requirement of the rectifier diode. Conversely in LV output designs (shaver chargers etc) the duty ratio can be pushed to the other extreme - A high PIV output rectifier can be used on the low voltage output side in order to benefit from minimising the troublesome reflected voltage across the primary-side switching transistor. Here endeth today's lesson of flyback SMPSU design!
> I'm actually running this one in flyback mode...
Then you should benefit from this effect.
-Richie,
GeordieBoy, Wed Jan 14 2009, 05:09PM
> Because the flyback pulse is magnitudes bigger than the forward one...
BINGO - Correct Answer! I thought that if anyone got that right it would be you!
Yes, the voltage waveform in a typical flyback converter is highly asymmetric. That is the forward voltage is relatively low in magnitude and applied for a long time, and the flyback voltage is very high in magnitude and exists for only a short time. The volt x second balance is maintained across all the windings still.
This property is one of the many reasons that the flyback converter is so popular in cheep PSUs and works well in the LOPT stage of TVs. In designs with HV output half-wave rectification can be used whilst minimising the troublesome PIV requirement of the rectifier diode. Conversely in LV output designs (shaver chargers etc) the duty ratio can be pushed to the other extreme - A high PIV output rectifier can be used on the low voltage output side in order to benefit from minimising the troublesome reflected voltage across the primary-side switching transistor. Here endeth today's lesson of flyback SMPSU design!
> I'm actually running this one in flyback mode...
Then you should benefit from this effect.
-Richie,
Re: Flybacks- Big & Small; Performance Analysis
Marko, Wed Jan 14 2009, 05:20PM
How many igbt's do I get for the answer? :P
It's because the negative half-cycle output voltage of the transformer is much lower, being only forward-mode voltage of primary supply voltage*turns ratio.
So the diodes only need to withstand sum of this voltage and DC output voltage.
In order to satisfy volt-second requirement, this off-period also needs to last proportionally longer than the high voltage pulse does. Hence, even the maximum duty cycle in flyback mode is limited by the diode ratings (although, in most flybacks, diode ratings seem to be fairly generous for some reason).
Running the transformer in forward mode with symmetric square wave on primary is, of course, much harder on the diodes for same output voltage.
PS. Now I'm beaten by Jan because of holding my reply up for 20 minutes :P
Marko
Marko, Wed Jan 14 2009, 05:20PM
The diodes used in this application ARE NOT required to withstand a reverse voltage of TWICE the DC output voltage like you would find with most normal half-wave rectifiers. Can anyone explain why?
How many igbt's do I get for the answer? :P
It's because the negative half-cycle output voltage of the transformer is much lower, being only forward-mode voltage of primary supply voltage*turns ratio.
So the diodes only need to withstand sum of this voltage and DC output voltage.
In order to satisfy volt-second requirement, this off-period also needs to last proportionally longer than the high voltage pulse does. Hence, even the maximum duty cycle in flyback mode is limited by the diode ratings (although, in most flybacks, diode ratings seem to be fairly generous for some reason).
Running the transformer in forward mode with symmetric square wave on primary is, of course, much harder on the diodes for same output voltage.
PS. Now I'm beaten by Jan because of holding my reply up for 20 minutes :P
Marko
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