simple feedback driver for flyback transformer

Here's my new driver for my FBT which uses feedback from the transformer. I hope to make an audio-modulated driver soon. :-)

The circuit came from http://www.powerlabs.org/flybackdriver.htm and/or http://www.sixmhz.com/flyback.html .

UPDATE (Mar. 9th, 2008; please read everything):

Sorry, I forgot to tell how to 'find' the coils needed for this circuit.

This circuit requires 3 coils: a primary coil ('input'), a secondary coil (high voltage 'output'), and a feedback coil (used in finding an appropriate operating frequency).

I'm pretty sure that all of the pins on the outside of a FBT are connected to sets of coils inside it. In order to find the coils needed for this circuit, check all of the combinations of pins to see if they conduct a current (have a coil between them) - like this: http://www.geocities.com/drewh0208/finding_coils_in_a_FBT.GIF

Once you have a pretty good idea about which pins are connected, experiment with different coil arrangements to see which works best (usually when the FBT makes the loudest pitch).

If you find a pin that isn't connected to any of the other pins, then, while the driver is running (with the primary and feedback coils hooked up to the drive circuit), CAUTIOUSLY bring the obvious high voltage output terminal (a heavily insulated wire sticking out of the unit) near that isolated pin and see if any sparks jump between the two. Make sure that the HV output doesn't arc to any of the other pins, especially the ones connected directly to the circuit, or else you could short out a whole lot of other things.

I haven't had any personal experience with FBT's with two heavily insulated wires coming out of it, but my first guess is that those two wires are both of the ends of the HV output and would arc to each other.

An alternative to finding coils (for the primary and feedback coils) inside the FBT is to wind your own coils on the exposed part of the ferrite core. Check out this site for an example of how many turns to wind: http://www.powerlabs.org/flybackdriver.htm

Sometimes winding your own coils will produce a higher voltage than using the built-in ones; it depends on the FBT, what kind of power you're using, your driver, etc...

Category:

Science & Technology

Tags:

• feedback
• flyback
• transformer
• FBT
• LOPT
• driver

[wistwc]

I don't understand why you need to take apart the flyback and then buy transistor and heat sink and a whole bunch of stuff (including batteries, such a waste!) to do this experiment. Won't it be simpler to use the original circuit and connect to the mains supply.

[drewh0208]

Yes, it would be simpler to just take the picture tube out of a TV and use the circuit as it is, but then not only do you have the dangers associated with high voltage, but now you risk being electrocuted by the mains (which delivers much more current than the high voltage transformer).

Using the flyback in some of your own circuit designs could lead to better control/results, and you wouldn't have to lug around the rest of the circuits from the TV you pulled it from.

[FenixZ2]

With all the monitors I've tried that with I can't get it to stay on because of the "Power Saver" thing, so i get about 5 seconds before it blinks off, know how to pass that?

[drewh0208]

Assuming that you've only disconnected the flyback from the CRT and have left it in the original circuit boards, I can't really help you in overriding the "Power Saver" thing - is there an enable/disable setting?

[CrashByron]

I don't understand your schematic? I could never figure out how to make a flyback work. Theres about 13 pins on the one I have. Holy Shit! this thing holds a charge! I just got zapped! Lol.. anyhow. what pins do I use?

[drewh0208]

The wires in the video have the same color as those in the modified schematic (0:04-0:08).

It's highly improbable that you have the exact same flyback transformer, so you could do two things: 1) find the amount of resistance between each pin to locate two sets of independent coils (see jnaudin,free,fr/lifters/labhvp­s/tht,htm), or 2) wind your own primary/feedback coils (see websites in video description). Just try different pin combinations with a low amount of power.

[Shroommduke]

how much power does this take,, 6v * 4A = 24W but does it use or require that much power?

does anyone know?

[motto25]

how do you determine the ohms of your resistors?

[motto25]

why dont you need capacitors?

[rockman378]

@drewh0208 hey i have a question; can the resistor values be 250 instead of 220 ohm's and 300 ohm's instead of 270 ohm's??

[Alex1M6]

@maleshmawa2007 Try switching the polarity of the connections to the coils.

[maleshmawa2007]

HELP!!!, am using the driver but when I power it (PC power supply), the flyback core get magnetized but no HF noise or arcs, what do i need to fix? am using an older transformer from black & white TV. thanks

[hardstyle905]

@31128Jeremy No shit sherlock. He's using 6V and a single transistor....

[sprogdiklis]

what type flyback ur using

[31128Jeremy]

the arc is small!

[MrSomeone4321]

thats not a neon tube thats a Xenon tube!!!