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Registered Member #3253
Joined: Wed Sept 29 2010, 12:21AM
Location: New Zealand
Posts: 13
Hi guys, I have a common modern CRT flyback transformer, with the U-shaped pin layout and have tried every combination of the pins with each polarity with a 555 driver. I found that the very first and last pins seem to give the highest output voltage, which is still barely enough to arc with 12v across the coil which is obviously far away from what its capable of doing.
My question is, what input voltage are these flybacks designed to run at? I get the feeling its much higher than what i've been trying, but would like to know before I crank it any higher. Also, what frequency are they designed to run at?
One last thing, when used in a CRT, its primary purpose is to create the electric field which accelerates the electrons I believe. In doing this, the HV side of the transformer does not conduct or arc since it is just applying a high potential across the plates, is it safe to assume that running a flyback with a continuously open circuit on the HV secondary will not damage the transformer?
Registered Member #162
Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140
Most modern flybacks use around 100 to150 Vdc as a supply for the primary.
Provided that you don't drive the coil at or near resonance (varies a lot, stay below 20 kHz for a TV lopt & 50 kHz for a monitor lopt) an open-circuit secondary is not a problem.
Also, once working, be aware that very few lopt are designed for 5mA or more output, so for reliability dont draw too much eht current. Due to commercial considerations, lopt are only just reliable at rated kV/mA.
As above, find the lopt part number, data for most p/n can be found via t'internet.
Registered Member #3253
Joined: Wed Sept 29 2010, 12:21AM
Location: New Zealand
Posts: 13
Hmm that sort of primary voltage is much higher then I expected, not suprising though. The part number is LCE CF1388, it has 10 pins in the U-layout and 3 for the adjustable focus & screen module.
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
V3rge wrote ...
Hmm that sort of primary voltage is much higher then I expected, not suprising though. The part number is LCE CF1388, it has 10 pins in the U-layout and 3 for the adjustable focus & screen module.
I looked in HR Diemen, and couldn't find a datasheet for you. To follow on from Sulaiman's comment, by far the most common primary operating voltage of modern LOPTs is 110V.
Registered Member #834
Joined: Tue Jun 12 2007, 10:57PM
Location: Brazil
Posts: 644
It's possible to operate at lower voltages at lower frequency, leaving more time for current buildup in the primary before interrupting the current. Or you can wind a new primary around the exposed core with less turns and operate at low voltage and high current.
Registered Member #834
Joined: Tue Jun 12 2007, 10:57PM
Location: Brazil
Posts: 644
Flyback transformers are not resonant. At least not at the frequencies where they are designed to operate. They are just transformers, usually with the output rectified.
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Modern flyback input voltage requirements?
