Author Topic: How to drive these flybacks?  (Read 443 times)

Offline Alberto

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How to drive these flybacks?
« on: October 27, 2020, 10:14:33 PM »
Hi everyone.

I have found these HV power supply. The first one from a laser printer and the second one from a ¿LCD? TV.





I have made drivers for classic CTR TV´s flybacks, but I have no idea about how to connect these. With classic CTR flybacks you can turn wire around the core. But here, I can´t, there is no space.

I can easily find the primary in the pins with an ohmeter, but I don´t know what kind of circuit use.

If you have any suggestion I will be gratedul


Kind regards

Offline ElectroXa

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Re: How to drive these flybacks?
« Reply #1 on: October 27, 2020, 11:21:00 PM »
Hi !
you can use drivers featured on this page to drive these flyback
if the flyback has only 2 primary pins, I would suggest using the 555 driver, as it can drive this kind of flyback, even at low power :)
http://uzzors2k.com/index.php?page=flybacktransformerdrivers

cheers, ElectroXa

Offline Alberto

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Re: How to drive these flybacks?
« Reply #2 on: October 28, 2020, 12:15:00 AM »
Thank you!

I will start with low voltages to protect the primary

Offline davekni

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Re: How to drive these flybacks?
« Reply #3 on: October 28, 2020, 08:29:08 PM »
Typical laser-printer ionizers run around -5kV, although I've seen higher voltages in large printers.  I don't know the typical circuit topology (flyback or other).

CCFL transformers as in your LCD TV board are not designed for flyback drive, having ungapped ferrite cores.  Some old designs drive them with Royer oscillators.  Newer designs usually drive them with half or full-bridge square waves in the 50kHz range.  Leakage inductance between primary and secondary windings combined with output capacitance makes a series-resonant circuit to get peak voltages of 2-3kV to initiate discharge in CCFL lamps.  Running voltage drops much lower, around 500V I think.  (Someone correct me if that's not accurate.)  I have used these CCFL transformers for continuous +-2kV output to feed CW voltage multipliers for static-electricity wands and for my small Marx generator.  Not sure how far they can be pushed, as they are designed for kV voltages only during momentary start-up.
« Last Edit: October 28, 2020, 08:38:29 PM by davekni »
David Knierim

Offline Alberto

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Re: How to drive these flybacks?
« Reply #4 on: October 28, 2020, 08:53:46 PM »
Ok, thank you!

Offline Atomillo

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Re: How to drive these flybacks?
« Reply #5 on: November 01, 2020, 09:04:48 PM »
From my experience, they usually have to equal primary windings. In the board, they are tied together at one point and Vcc is applied there. The other two extremes remaining are switched on and off periodically to ground.

They also tend to have low inductance and as davekni remarked are operated in a resonant manner. I've been able to reuse the circuit on the original board by removing the driver and injecting the signals onto the gate of the MOSFETs.

The maximum voltage depends on the transformer. I've used some for up to 3kV for powering various nuclear detection instrumentation. You can very slowly increase the voltage on a quiet and dark room. At some point, corona hissing will become audible. Examine your connections. If corona comes from wires or joints outside the transformer, solve the issue and increase the voltage. As soon as corona is visible from the transformer, STOP INMEDIATELY, or it will destroy the insulation.

Offline Alberto

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Re: How to drive these flybacks?
« Reply #6 on: November 02, 2020, 11:32:51 PM »
Thnank you.

I have started with the LCD TV. I tried to drive it with the first driver from the link of ElectroXa, but the driver operates between 10 and 33Khz, and I only see very small arcs (1mm) at 10 Khz, so I think it needs a lower frecuency. This week I´ll try to modify the driver to give less frequency.   

Offline davekni

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Re: How to drive these flybacks?
« Reply #7 on: November 02, 2020, 11:37:41 PM »
The CCFL (TV) transformers I've measured in-circuit ran at 60kHz, so higher, not lower.
David Knierim

Offline Alberto

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Re: How to drive these flybacks?
« Reply #8 on: November 04, 2020, 12:07:26 AM »
Is strange, because at higher frecuencies I don´t see any arcs.

I´ll try diferent frecuencies and I will tell here

Offline Alberto

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Re: How to drive these flybacks?
« Reply #9 on: November 09, 2020, 12:06:28 AM »
I have built my first oscillator (With a 555) ant it gives from 10 to 500 Khz.

I only get very very small sparks so I think it isn´t a HV transformer, but what is the working voltage of CCFL?

But the small flybacks from the printer works great.  20Kv (The sparks are bigger than 2cm). 4 turns of AWG20 12V and beteewn 63 and 77 Khz


Offline Alberto

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Re: How to drive these flybacks?
« Reply #10 on: November 21, 2020, 08:36:42 PM »
The CCFL (TV) transformers I've measured in-circuit ran at 60kHz, so higher, not lower.

I have tested the CCFL transformer and the best results are with the lowest frequency that my oscillator can archieve. Around 650 Hz. The spark is only 4 mm long.


But I want to know how these transformers work. I don´t know why it can give thousands of volt from just 10 volts because I think the turn realtion is very low for that. I have looked up in internet but I don´t find any source. Only webs about desing, but not about how they work

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Re: How to drive these flybacks?
« Reply #10 on: November 21, 2020, 08:36:42 PM »

 


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