Driving a CRT monitor flyback transformer with squarewave

Yes, if I needed one for a stage prop, or quickly, but sourcing a s/h neon xformer in a country town? I dunno where to look...

Grant.

Over here we don't have oil furnaces in common usage, and oil heating virtually disappeared after the '70s oil price rise, in favour of natural gas heating. Central heating likely gas or electric reverse cycle airco.

Neon xformer commonly recommended for Jacobs ladder, otherwise it's an auto ignition coil or old TV tripler with some 12V high current power driver circuit.

I've got some high voltage gear recovered from laser printers, but the current used in them there is very small. No good for drawing big sparks.

Grant.

Or put the ladder inside an acrylic tube to shield it from the breeze?

Benefit too of limiting ozone generation, or emission, I imagine.

Grant.

I have an uncle, he's ~87 now, who would take a three-corner file and slowly file open the vacuum teat (sis-s-s-s-s-s :-) ...Jim Thompson

Most country towns I know have bars :-) Just find an old sign where the tubing broke. ...Jim Thompson

I don't believe I've missed the point at all. The voltage appears because the current cannot change instantenously. But the ratio of voltage on the primary and secondary remains.

Others have pointed out that the OP is on the

In what respect is it wrong? In particular, is there any conceivable circuit that allows the secondary to present a high voltage while not having the primary present that high voltage divided by the turns ratio?

Sylvia.

Can't imagine getting a file inside the connector (vacuum it inside the socket?), but why not jam in a screwdriver and break off the tit and let the vacuum out? I'm not quite sure I want to try that -- perhaps inside the wheelie bin with protective glasses on in case it goes Bang!

And I have a monitor in the car, awaiting destruction... Something different today?

Grant.

Back in those days, the CRT's had octal bases. Unsolder and pull it off, exposing the vacuum teat. ...Jim Thompson

Wimp. All you need is a small triangle file or a big pair of diagonal cutters. I used to have fun filing a notch into the tip where the air was evacuated and letting them hiss for hours, or days. :)

Why? To watch cat or dog turn their head on a cute, angle trying to figure it out? >:o)

Grant.

Yes, but...

adjustment,

The other keyword you overlook: tripler.

CRT HO drives that high voltage tripler, what's inside of that? A little more than the crappy so-called efficient 555 circuit from a web-site that holds one of the worst collections of circuits I've seen on the Internet. Not a place of learning.

So the simple steps to driving a CRT are to drive primary to some current limit, You may need to add your own low voltage primary around the exposed ferrite for

So, turn current old until some current limit before saturation, turn off current, collapse of magnetic field generates very high voltage, repeat at some frequency that suits how you see the circuit, watching on a CRO is good, or simply tuning for minimum input for big output.

The open loop 555 or whatever drive is not do good, as you really do want to switch off input power before saturation of the ferrite, otherwise you're simply going to burn something.

You can see saturation as unreasonable current draw, or with a CRO a breakpoint from gentle linear ramp to steep almost vertical ramp of input current.

Maximum efficiency is charging the ferrite so some value below saturation.

Thus driving the primary open loop from an oscillator is bad. Better is using a latch that you set at a regular rate, and current limit resets latch, Q drives the output transistor, and voltage feedback tells you how long before setting the latch again for variable frequency, ort also clears the latch for fixed frequency. This is standard power switching topology stuff.

Other way is at a fixed frequency into a tuned circuit which is how the CRT does it, I think. There it was a controlled oscillator with a tight frequency spec with a BTW we can also make some EHT here too, due to the large amount of energy circulating to produce horizontal scan driver to the yoke coils.

This pulse train pumps up the energy through the tripler and makes your high voltage of 26kV max for low xrays from the CRT in original app.

Efficiency comes from driving a tuned circuit so you need a proper snubber and/or tuning to work with the primary side issues. Of course adding you own low voltage primary sidesteps the noticed high voltage seen on existing driver.

But before you argue about the thing cannot work, it did work as a CRT EHT source until OP pulled the parts from PCB.

I've written the above from memory, so the might be minor errors. But I'm trying to explain the general picture, not give a precise working guideline -- for that I'd have to drag out gear I got here and have a play. I have other things on my todo list right now.

As far as voltage multipliers go, I used them very recently to make a 40V IC generate over 100V to drive 50 LEDs in series at 20mA, 36V chopped DC stepped up from 12V though a tripler with over-voltage feedback and LED current regulation.

This stuff is not rocket science. But EHT adds some corona and visible sparks that very much add to the excitement. I hope the above ramble has some useful points to help OP.

Grant.

adjustment,

I've already suggested to the OP that he look at voltage multipliers, so I cannot be overlooking triplers.

limit,

The issue is not the voltage driving the circuit, but the voltage tolerance of the switching transistor.

Specifically, the OP is seeing that when the transistor turns off, the primary voltage rises to a level where the transistor is destroyed.

The OP is trying to get a particularly high voltage *on the secondary of the transformer* without the voltage on the primary destroying his transistor. I'm suggesting that this goal is misconceived (aside from getting a transistor that tolerates a higher voltage).

Sylvia.

Michael A. Terrell expounded in news:596dnbbEmYPTHgbQnZ2dnUVZ snipped-for-privacy@earthlink.com:

What do you think I was using?

I never got that brave.

I didn't see any point in waiting. The whole point was to be able to put it out at the curb for safe disposal. Not sure they would even take that today, they're so fussy now that they're sanitation "engineers".

Warren

I'm talking about one from my set of needle files.

The point was that some people wnadered into part of the shop they were told to stay out of. A hissing CRT scared the crap out of them. :)

Does a leaky air hose do the same?

The one I did yesterday suddenly gave way (using a big flat file) and the hissing only lasted maybe ten seconds... Fun?! Don't think I have the patience to attack the tube with a tiny needle file. I put photos up of the switched capacitors stuff too, from upthread, on:

Grant.

Do they implode & sent glass shrapnel all over the room?