Flyback transformer usage

Discussion in 'General Electronics Chat' started by electronis whiz, Apr 28, 2015.

  1. electronis whiz

    Thread Starter Well-Known Member

    Jul 29, 2010
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    I have an old PCB, flyback from an old TV I had found a case for the entire original board, but it's a bit bulky, and I'd like to combine this with another HV source into one unit. I found a datasheet on a flyback, but I'm not sure what all of these pins are for. It looks to ba a fairly standard setup for a flyback.

    I'm not really understanding the data sheet as to what the pins do and where I would connect an input. I assume the horizontal output transistor is what drives this as to my understanding it works sort of like an SMPS.

    Data sheet: http://www.mokuai.com/en/product_show.asp?nid=308

    My goal for the project is to find out the connections, build some sort of a driver circuit preferably with some way to adjust the voltage.
     
  2. Hypatia's Protege

    Distinguished Member

    Mar 1, 2015
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    Inasmuch as the core is inaccessible and the existing (LV) windings aren't 'amenable' to Royer topology, the best approach is implementation of true 'flyback' topology...
    A current mode PWM controller in conjunction with a MOSFET (and a carefully designed 'snubber') will produce very good results -- Otherwise, should you wish to 'keep it simple', a 'plain vanilla' 555 driven MOSFET (or, even, BJT) circuit will provide satisfactory results in many applications... --- Of course, whichever method you choose, you'll need to use a winding (or winding segment) exhibiting current-handling capability and impedance appropriate to your application/driver...

    Best regards
    HP
     
    Last edited: Apr 28, 2015
  3. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    if its a Lopt ( line output transformer) it will be tuned to run at approx 15Khz and fed with a square wave using a mosfet or bjt, most likely at 100 - 200v dc.
     
  4. Hypatia's Protege

    Distinguished Member

    Mar 1, 2015
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    While the above is indeed descriptive of a flyback's (typical) 'native operating environment' -- Selection of other windings/taps allow operation at much lower primary EMFs -- Also, these 'beasties' are quite 'frequency agile':)

    Best regards
    HP
     
    Last edited: Apr 28, 2015
  5. electronis whiz

    Thread Starter Well-Known Member

    Jul 29, 2010
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    Many of the simple homemade driver's I've seen are basically super simple mosfet feeds it, another winding gives feedback and runs like that. They seem to work, although unless added a capacitor and potentiometer and change the frequency and power. Most seem to run on like 12V.

    I like the simplicity, but just can't see it having much modification or adjustment potential. Part of me wants to just reverse engineer the existing driver and reuse the existing mosfet, heatsink and find what drives the mosfet. I think the CRT brightness relates to the output voltage of the flyback somehow. Would seem that would make a perfect driver if can rework it.
     
  6. Hypatia's Protege

    Distinguished Member

    Mar 1, 2015
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    Yes, you're describing a basic 'half' Royer (q.v.) circuit --- You may control the output via control of its supply...

    CRT intensity control is archived via bias -- the accelerating anode potential is not controlled (beyond 'loose' regulation)

    If you want a reasonably efficient adjustable HVPS my suggestion is that you implement a driver employing current-mode PWM topology...

    Best regards and good luck!:)
    HP
     
    Last edited: Apr 28, 2015
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  7. electronis whiz

    Thread Starter Well-Known Member

    Jul 29, 2010
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    That's sort of what I was thinking it would need to be a PWM circuit like used for motor control, etc. It would be nice, although not sure possible just use a household dimmer switch. I don't know how it would deal with the inductive load, but basically they are just a PWM module. I don't know you can drive a flyback at 120V even if could compensate for the odd load with a reverse bias diode.

    Could maybe use parts of old SMPS unit, but still not sure how I could alter the output as they all seem to be just feedback operated via opto isolator.
     
  8. Hypatia's Protege

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    FWIW I use a (TI) uc3844 PWM controller in conjunction with an IRFP260 in the flyback driver for my radiography equipment PSU...

    Said arrangement will drive an LOPT to at least 50kV (many transformers will withstand as much as 80kV) --- at appreciable current.

    Two caveats:

    1) Proper 'subber' design cannot be overstressed!

    2) Because you will be using a transformer incorporating integral rectifier{s} it is critical that the driver is connected for the correct polarity! --- Note that it is the asymmetricallity of the drive signal that allows production of very high secondary EMFs sans excess of the reverse breakdown specification of the (internal) rectifiers...

    IMO thyristor arrangements will be of little use in driving ferrite transformers/inductors...

    Best regards, and, again, good luck! -- It's always nice to meet another HV/TC enthusiast!:)
    HP
     
    Last edited: Apr 28, 2015
  9. electronis whiz

    Thread Starter Well-Known Member

    Jul 29, 2010
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    I'm just getting into HV stuff. Between watching The geekgroup's youtube videos and photinicintuction it looks interesting. I have a friend that's a master electrician that has said he'd like to build a tesla coil someday too.

    I haven't really decided what I'll do with my supply, besides make sparks. I have an old laser tube that needs like 1500V to run so could be something to use to power that. Maybe use it to destroy some old junk electronics, I would think could use it to erase optical disks and maybe HDD platters too.
     
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  10. Hypatia's Protege

    Distinguished Member

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    Dear old 'PHOTON':cool:... Somewhere there's a straitjacket with that dude's name embroidered on it!!!;););):D

    Best regards
    HP:)
     
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  11. #12

    Expert

    Nov 30, 2010
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    I simply attach the offending part to a zip cord with alligator clips and plug it into a wall socket that is switched on from a different room. It's difficult to appreciate the, "BANG' from the next room, but the confetti is just as pretty as you might expect.
     
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