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Registered Member #1389
Joined: Thu Mar 13 2008, 12:50AM
Location: Pittsburgh, PA
Posts: 346
I was cruising around the HVWiki a few hours ago, looking for something that I could build from my box of junk, which mostly consists of computer PSUs and boards from CRT monitors/TVs. Well, I came across the Royer Oscillator article and thought, "I have a bunch of high power HOTs... eh, what the heck, why not?" So as a result I ended up with a Royer flyback driver using HOTs. I still have a lot of fine tuning to do, but I've managed 1cm-1.5 striking distance and up to 4cm stretching the arc. Depending on set up, I've managed huge amounts of corona from up to 8 or 9cm. I believe the flyback came from a back projection TV. One HOT is 750V 18A and the other is 600V 16A.
At full power, the HOTs disipate a fair amount of heat, but not enough to worry about until I run it past 30 or 40 seconds. They are also running far below their ratings, so I am not too worried about them, not to mention the fact that I have like 30 more in my basement.
Currently configuration: 6+6 turn primary with 3 turn feedback, no capacitor to 5.6nF. Power is the rectified output of a 180W Lionel transformer, up to 20VAC. Current draw at 20VAC setting (voltage droops to 13VAC) is 12A.
Registered Member #834
Joined: Tue Jun 12 2007, 10:57PM
Location: Brazil
Posts: 644
Useless? These transistors are very useful for high-voltage projects. Are the right ones to use in flyback drivers, otherwise they would not be used in the applications where you found them. Their only problem is a quite low HFE.
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
I think the 1500Vpk ones like BU508D which can pull 8A are great. It has an hfe between 8 and 30, and drinks a mere 4A into the base - a good way to keep down winter fuel bills.
It will motor along like that 24/7 for months and years, which has a lot to commend it, in my view.
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
BJT's are mostly inferior to MOSFETs for switching applications. They need big base currents, are not very fast compared to FETs and have collector "tail" current.
I once tried to replace a FET in my experimental single transistor forward converter flyback driver with a HOT, and it did almost smoke and then popped. I had proper base drive with negative voltage etc... These things are just sooooooooooo slow....
Registered Member #1225
Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253
I have made a very very simple sstc with them, and could get a fair amount of breakout. It does not heat to badly, and i used 1n4007's as all the diodes. But if you make this do not use 1n4007's, they are much too slow. Use uf4007's or something fast like that. The current they have to carry is small, so one diode for each on the schematic is enough. Just replace the SU169 with any HOT that you have. I tried it with a 9 amp 1200 volt HOT iirc. I blew one, but that was only due to shorting something on the board out. It uses feedback, so no manual tuning required, other than tapping. I was going to post a thread about this a long time ago, guess i never did. Since this circuit uses so few parts, it would be good for putting in a small box and made portable for wireless lighting demonstrations etc. Oh, also you should use a big secondary, or small secondary with many turns to keep the running frequency down for the HOT's as they are not made for very high frequency.
Just a fun little project, not much. Great for a first sstc even though it has small output.
Registered Member #1389
Joined: Thu Mar 13 2008, 12:50AM
Location: Pittsburgh, PA
Posts: 346
Sorry. Whenever I've asked around for something to do with these otherwise excellent looking transistors by their datasheets, I haven't got much in the way of replies, so it seemed like there wasn't much to do with them. I'll change the title to extra.
Registered Member #1225
Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253
Firefox wrote ...
Sorry. Whenever I've asked around for something to do with these otherwise excellent looking transistors by their datasheets, I haven't got much in the way of replies, so it seemed like there wasn't much to do with them. I'll change the title to extra.
Why sorry? :P I don't think you offended anyone.
I am trying to think of something else that i saw using them, but i don't remember. I'll get back to you on that.
Registered Member #1389
Joined: Thu Mar 13 2008, 12:50AM
Location: Pittsburgh, PA
Posts: 346
Heh heh. I suppose not, Arcstarter. I'm working on that TC switched by a HOT, but I don't know if my Fres is going to be too high for it. I'll find out in a few hours, in anycase, since I still have around 10 or 15 of them. When I am done, I may try to hook my Iggy coil to the Royer oscilator with a small inductor for the second half of it. Now if only I had two iggy coils...
Registered Member #1225
Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253
Firefox wrote ...
Heh heh. I suppose not, Arcstarter. I'm working on that TC switched by a HOT, but I don't know if my Fres is going to be too high for it. I'll find out in a few hours, in anycase, since I still have around 10 or 15 of them. When I am done, I may try to hook my Iggy coil to the Royer oscilator with a small inductor for the second half of it. Now if only I had two iggy coils...
Well, i used a pretty small secondary, with i think 350khz, and it worked pretty well even just pulling like .5 amps from 12 volts. Got some breakout. But rewound microwave transformers are the stuff :). Suggestion, with mine, at first i did not smooth it enough and it would not work well, suppose it had something to do with feedback. I do not mean it didn't work well, nothing that is not smoothed will, but there was no corona, the HOT heated badly, and not much of any spark.
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Something to Do with All Those Extra HOTs
