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While this circuit isn't an ideal way to drive neon tubes (best with argon/mercury tubes) it does provide a super cheap and rugged way to make your own tube driver. It should be noted that this.
The schematic has been updated to include basic transistor protection in the form of a capacitor and diode. The step 9 page 'going further' now includes a way to measure these illustrious voltage spikes with a regular volt meter.Intro This instructable will show you how to make a simple driver circuit for obtaining high voltage arcs out of a component called a flyback transformer. A flyback transformer, sometimes called a line output transformer, are used in older CRT TV's and computer monitors to produce the high voltage required to drive the CRT and electron gun. They also have auxiliary low voltage windings built into them which the TV designers use to power other parts of the TV, they are usually customized for a particular model of TV. For the high voltage experimenter they are used to make high voltage arcs, which is what this instructable will show you how to do with just a few simple electronic components.
You can get flyback transformers out of older CRT monitors and TV's. They are the ones that have a big heavy chassis. There are also other instructables on this website showing how to remove them from the chassis and circuit board.Disclaimer I am in no way responsible if you mess up with this circuit. If you mess up you have no-one to blame but yourself. Supplies:1x Flyback transformer.1x Transistor, I've personally tested MJE13007, 2SC2373 and MJ15003. MJ15003 was by far the best performer with this circuit, it just seems to have the right parameters to produce the best output without getting too hot.
What you will need:1x Flyback transformerFrom an old CRT TV/monitor or purchased online (don't get ripped off, these things are worth about $15 max when new). TV flybacks seem to perform best with this circuit, monitor flybacks don't put out as much.1x Transistor such as MJ15003.2n3055 is the classic transistor often paired with this driver on the internet, but the 60v rating really limits its usefulness and more often than not results in it being destroyed. The peak collector to emitter voltage easily soars above this 60v rating and clips when the transistor breaks down causing extensive heating and eventual failure of the device. So please don't use it, if you do you'll need a large capacitor like 470-1uF across it to limit the peak voltage. This will make the arcs very small too.MJE13007 is ok but doesn't perform as good as MJ15003 without further modifications.NTE284 and 2N3773 are reported to give similar performance to MJ15003 whilst KD606 and KD503 are said to be the best with this driver. Wind two separate coils on the core, one in one direction and one in the other.
Don't worry about getting it mixed up as you can simply flip the ends later on. There is no one size fits all when it comes to number of turns, but 8 turns primary and 4 turns feedback is a good starting point for 12v, a bit less of both for 6v and a few more primary turns for 18v. Experimentation is recommended.If you've used enamel coated wire like I did then use something sharp to scrape away the enamel insulation at the ends. I don't recommend enameled copper wire for homemade windings as the insulation layer has a habit of being scratched off by the edges of the core and shorting to it, plus its expensive these days! Apply a dab of thermal compound or insert the thermal pad now, then mount the transistor onto the heat sink.The heatsink is important as the transistor gets hot.
I just bought the cheapest heatsink I could find, but bigger is better. The transistor I used is of the TO-3 case styleDon't let the legs of the transistor touch the metal heatsink when tightening the screws or else you'll be shorting the base and emitter to the collector. I just used some random screws and nuts I found in the garage, but they're pretty cheap on places like ebay or local hardware stores.Q: Can I use a PNP transistor? A: Yes, but you will have to essentially build the circuit backwards for a positive ground.Q: Is the heatsink really needed? A: Yes, if you are wanting to use this circuit for more than 10 seconds the heatsink is vital as the transistor gets hot.Q: Can I use a MOSFET?
A: No, a MOSFET will not work for this circuit (other self oscillating circuits designed for single MOSFETs are out there). To power the circuit I recommend a power source which can supply a minimum of 2 amps, lower will most likely work but will limit the output.Add more turns on both windings to increase power, (contrary to what I've read online), this lowers the operating frequency and allows more primary current to ramp up. The number of turns appears to give a rudimentary form of adjustable current limiting.Bench power supply Self explanatory really.Wall Wart/charger You can use these, but be mindful of their voltage and current ratings. The switched mode variety will most likely go into self limiting/shut down if the maximum current rating is exceeded.Salvaged transformer Done this myself for my 12v driver, a 48VA transformer which puts out 9v AC will give roughly 12v DC 3 amps when rectified and smoothed. A 4700uF 25v capacitor will give plenty of smoothing, I'd go with 50v 4 amp bridge rectifier diodes minimum.Lithium cells in series are great as they can supply lots of current.Drill batteries are fine, most are 18v so use the 18v circuit.
AA batteries in series are fine, the arcs will just gradually become smaller and smaller as they become depleted. An AA cell is considered spent when it drops below 0.9v at rest, but many can still power other loads even when they're no longer able to supply the juice for this circuit. A 12v lead acid battery is a very good way of powering this circuit and is what I personally used.12v car battery see above.6v lantern batteries will power this circuit for a long time before the arcs start getting small. These are not too common nowadays and pretty expensive in many places, don't waste your money if cheaper options are available!AAA batteries will work for a while but won't last as long as the larger AA cells, they also have a higher internal resistance so will waste more power as heat.9v/PP3 batteries will give a few minutes play when new before the arcs become smaller and the circuit stops working.
The upper resistor will probably need to be around 180 ohms for 9v, but I didn't make a 9v driver schematic as it would probably lead people to using 9v PP3 batteries and disappointment. When drawing arcs. I strongly urge you to make a 'chicken stick' which is an insulating stick of some sort where you can tape the high voltage wire to the end of instead of touching it directly. PVC pipe is very good for this, wood is fine too as long as its dry. Sharp pointed nails work well and give slightly larger arcs than rounded electrodes, I used a piece of scrap metal for mine. Attach one end of a wire to the chicken stick electrode and the other end will be attached to the HV return pin on the flyback transformer (either solder in place or use an alligator clip or terminal block). Scary warnings.
Including the obvious risk of electric shock another thing to take note of is the arc is VERY hot and can easily burn or set to fire to anything it touches. Even the cable insulation will burn if you draw the arc onto it. If you insist on burning pieces of paper or other objects take that into account and have some way of putting the fire out.
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Never touch the high voltage wire or any of the flyback base pins when the circuit is turned on. Make sure you can easily cut power to the circuit. Do not use this circuit on an unsuitable surface such as a bare metal or easily flammable surface. The transistor heat-sink can get hot, watch out not to burn yourself. The primary coil and transistor collector can ring up to a few hundred volts, don't touch these either. Keep any high voltage cables away from other parts of the circuit.
Keep pets away. As well as the risk of shocking your pet from the sparks many household pets like to chew things such as wires, the high frequency noise can upset many animals too.Disclaimer I am in no way responsible if you mess up or hurt yourself or others with this circuit. To find the high voltage return first attach your chicken stick to the high voltage out (the big thick red wire) and turn the circuit on.
You should hear a high pitch noise, if you don't hear this noise then go to the troubleshooting page at the end. Bring the chicken stick close to the pins on the flyback and go past each one individually. Some of them may give a slight spark but one of them should give a solid constant HV arc, this will be your HV return pin. You should now disconnect your chicken stick from the HV out and connect it to the HV return pin instead. In the images above are some arcs produced by my driver and some different flyback transformers, most flybacks will give around a 1-2cm arc with 12V input and upping the input voltage only increases heating on the transistor in my experience. Have fun and remember the heatsink may become too hot to touch.
Problem?. If nothing happens then try reversing the connections to one of the coils. If it works but the arc is small try reversing both the primary and feedback coil connections. Around 2cm is the maximum arc length you are going to get out of this driver, 1cm may also be the maximum on some flybacks. Also try adding more turns to both coils, this lowers the operating frequency and allows more current to ramp up in the core. Make sure all connections are secure and nothing is shorting out.
Enamelled copper wire is notorious for bad connections, soldering doesn't always break through the enamel. I use a knife to scrape some off and prepare for a good connection. It works but the transistor gets very hot. This is normal for this circuit, the price to pay for a simple design!
The way the switching cycle ends is by the transistor coming out of saturation as the collector current increases beyond a certain point, a transistor passing a few amps out of saturation will cause heat. To combat this add more thermal mass to the heatsink, either by swapping it for a larger one or attaching more metal to the current one. The 22 ohm resistor gets hot, this is normal. It my case it dissipates 1.96w, but that's enough to get most little resistors too hot to touch. If you're not comfortable with components running too hot to touch then increase the thermal mass, in the resistors case increase the wattage rating.
Broke the core? Glue it back together, dampening the mating surfaces with water first will help certain types of glues stick. Ive built a very similar jacobs ladder using a different video, in which 2 wires are connected to the standard pins of the flyback transformer (pic attached to explain) there is then a single cable of roughly 6 windings around the core and it shown to be accross the middle of said core, whereas you have 2 seperate windings that seem to be left and right of the middle of the core.
(the different transistor, lack of diode and windings are the only differences in the circuits) yours also seems to have bigger arcs and i was wondering if you could explain why so i could improve mine? I am using a 12v power supply and a s2055N transistor. My circuit does not have no appear to need a diode but would adding one help? Any other way i can increase output voltage like adding a capacitor? Hi, sorry I haven't been active in this scene for a very long time but just noticed your comment when I logged in for the first time in years.
Your transistor appears to have that diode built in, it's also a horizontal output transistor from the TV and can be finicky to oscillate with this driver. Winding external primary and secondary coils often works better with lower voltages due to the lower inductances, number of turns can be a bit experimental and some transistors work best with more or less.
How big are the arcs you're getting? The flyback in that video had something like 20 primary turns and 7 feedback. This allowed the peak primary voltage to reach higher levels and thus give more voltage on the output. Before doing this please see the updated schematic with the capacitor and method to measure peak collector-emitter voltage on the going further page, I know the instructable is a bit messy and inconsistent now and I'm thinking about updating it during the coronavirus lockdown period. Its important the correct capacitor value is selected to prevent the transistor from being destroyed by overvoltage.
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