Flyback Driver Circuits

High Voltage with a Television Flyback Transformer


 1 Sept 2003 

Table of Contents

Safety: Safety is extremely important - a flyback is not a toy!
 Introduction: Basic Introduction of flybacks and the driver circuit
 Flybacks: What are they? How to get one? How to use it?
      - (Frequently asked question: What on earth is a Flyback?)
 Flyback preparation: Get your new flyback ready for use
 Circuit 1:  Ultra simple Single Transistor flyback driver circuit
                         - Parts you will need, and how to get it working *updated!*
 Circuit 2:  An even simpler circuit if you have a SMPSU
 Testing and Results: Pictures and Videos of experiments *updated!*
 Others:Other experiments and cool stuff
                     - The Jacob's Ladder
                     - The Ion Motor*new*
                    -
 The PLASMA GLOBE (another page)

Safety

Disclaimer: A flyback is not a toy. You must accept the fully consequences of your actions should you build a flyback system.

The first important thing to note is the high voltage. Extremely high voltages of 40kV can be generated. 40kV is more than enough to jump a rather large air gap! Although the nominal output current is not that high, around 10mA at most, it is still dangerous. Furthermore, the output is of high frequency (20kHz +) and our nerves are not very sensitive to it. Hence very little or no sensation of shock is felt, even as significant currents flow through your body.

Secondly, the arc itself is a danger point. Arcs are plasma, and has temperatures of thousands of degrees. Although the low current associated with  the flyback makes it small and therefore not too destructive, it will easily set on fire any flammable materials, like insulation. High voltage burns through insulation like nothing. Also, any wood which comes in contact with the arc will also catch fire.

In addition, since the arcs can jump a gap, and is very hot, contact with the arc will immediately burn the arcing points. The injury (mostly burns) may be small, but it can cause one to involuntarily jump or jerk away from the power source, and hurt himself by knocking whatever is behind him. Also, the high voltage arc will destroy most electronic equipment or electrical appliances it comes in contact with, directly, or indirectly.

Finally, although the overall device isn't very dangerous if precautions are made, it can become lethal if a high voltage capacitor was charged. Even small capacitors can discharge several thousand amps and can cause heart fibrillation. Hence, the use of cascades to multiply output voltage, or connecting capacitors for pulse discharges is highly discouraged for beginners!


 

Introduction

This is probably one of the best and easiest project for someone who is familiar with electronics, and wants to venture into high voltage. It requires little skills to set up the circuit, and only simple adjustments concerning the circuit is required. Although the power involved may not be very high (especially the low current due to the thin windings of the flyback), a small mistake might cause severe Radio Frequency (RF) burns. However, if safety precautions are taken, some marvelous high frequency arcs can be generated. However, if you have never experimented with HV before, I recommend you start with a less dangerous electrostatic project.

As far as I know of, this should be the easiest circuit with which a high voltage output can be achieved. The original version of this circuit used 2 transistors. Burak (link to the page) modified it to work with a single transistor making it even easier and cheaper to build.  Sam at powerlabs has also done the same circuit and has also achieved some very nice results with a nice flyback.

The flyback transformer operates at high frequency, unlike a normal transformer. As such, the input has to be of high frequency. This has to be generated by a circuit, and in this case, a  one transistor circuit. The one transistor circuit is easy and cheap to build, but has some drawbacks. When operated at higher inputs, the transistor tends to overheat and die (it gets very hot)... but still, it works great for many things such as drawing arcs, making ion motors, running cascades, charging HV caps, small Jacob's ladders, plasma globes and perhaps a small tesla coil, or a marx generator.

On the right you can see the schematic. That's how easy it is!

The principle of operation is as simple as the circuit itself:

When powered is applied, the transistor will conduct current in the flyback primary, through R1 and R2. This induces a current in the secondary windings and the feedback winding. The feedback coil will generate a current, which will trigger the transistor to stop conducting. The magnetic field in the ferrite core collapses and a HV spike will appear on the secondary windings by induction. Also, there will be no longer any feedback current on the feedback windings, and the primary conducts again. This cycle repeats several thousand times a second, and the cycle will repeat at a  natural frequency. By having such a feedback system, adjustments are minimal, and the circuit becomes dynamic. This can easily be seen as the frequency of the arc grows higher as the arc is drawn. The arc then becomes ultrasonic is drawn longer.

 

Flyback Transformers

The heart of the circuit is a ferrite-cored flyback transformer. There are several different types of flybacks, and any device using a cathode ray tube will contain one (this includes oscilloscopes, televisions, monitors, and others). There are many types of flybacks out there. The really old ones have disc shaped secondarys, removable primarys, no rectification (or a removable high voltage rectifier) and might look something like this:

Most computer monitors and televisions nowadays use flybacks which have the high voltage rectifier built in. Although a HV rectifier is useful if you want to charge up capacitors or experiment with ion streams, having the rectifier built in is not desired for most high voltage experiments, as it will make the output half wave, and in that way make the output voltage ~55% lower than it would be without it. The peak power remains the same, and adding a filter capacitor can correct that problem, but it also requires a resistor to limit the current drawn from the cap during arcing, and it is a pure DC supply, useless for plasma globes and other experiments requiring AC. The CRT on TVs and monitors is also a high voltage capacitor, and you could use it as such in an experimental HV DC power supply. Also note that the even newer flybacks out in the market today have the voltage divider and focus control built in. Some don't even have the core visible - these are useless for this circuit.

So, overall, flybacks with built in rectifiers are still usable, but you should look for one that has either a removable rectifier (sometimes the rectifier is inside a tube that sticks out from the flyback, other times it is encapsulated in epoxy next to it. Either way, removing it is a good idea if you're able to). The best flybacks come from old TV's or monitors, specially the larger ones, and have a disk shaped secondary. Black and white TV flybacks tend to have a higher internal capacitance and higher step-up ratio, whilst monitor flybacks are not very useful, as far as the modern ones are concerned. If your flyback was used in association with a cascade, you can expect to obtain no more than perhaps 15kV from it (with 12V input). However, if it was free-standing, over 30kV may be obtainable (with higher input voltages). Nominal output current is 1-2mA, and arcing current can be as high as 10mA and above.

Here is a picture of some of my flybacks:

I will be using the 'olden flyback'. As you can see, the secondary is much fatter than the modern flyback. Disked Shaped secondary flybacks (like the one shown previously) are even better. The fatter secondary usually indicates a larger number of secondary turns and a  proportionally higher output! Unfortunately, these flybacks are very difficult to get nowadays and therefore I shall use my existing one for the time. (Got them for $5 each at the junk shop). Looking at the modern flyback, the HV output is usually connected to a 'horn'. You can use a multimeter to find which is the secondary ground. Connect one to the HV output and test all the pins at the bottom. The one with a big resistance is the secondary ground. This particular model is rectified.

Now where do you get the flybacks from? Either find one at the junk shop, or get one from an old television. The best flybacks come from the big olden black and white TVs. Older is usually better.  However, note that if you remove your flyback from an old TV it may well have it's secondary winding burned out... Flybacks are built tough, but they are high voltage parts, and as such they tend to have a limited useful life. If it is the primary that is burned out, than it may simply be removed as you will wind a new one either way. The general rule of thumb: The fatter the secondary, the better.

But what on earth is a flyback?

Basically, a flyback is a high voltage Line OutPut Transformer (LOPT), which powers Cathode Ray Tube (CRT) filaments (basically, powering all those televisions and computer monitors). A flyback is a special transformer which in conjunction with the horizontal output transistor/deflection circuits boosts the low voltage power supply to the 10 to 30 KV for the CRT as well as provide various secondary lower voltages for other circuits (that's why there are so many pins at the bottom of a flyback), which power the logic, tuner, vertical deflection circuits, video signal, and CRT filaments. A flyback outputs high frequency (AC) high voltages which must be converted into DC by a rectifier to be used by the various components.

In this case, we are using the main High Voltage source. Olden flybacks have removable rectifiers which make them ideal for powering plasma globes (requires AC) and Jacob's ladders, and most modern flybacks have a build in rectifier or uses a voltage multiplier, in which will not be very useful except to power ion motors and such.

For more information on flybacks, read this excellent page.

 

Preparation of a Flyback

Before using the single transistor circuit, some preparation has to be done about the flyback.

First remove the original primary winding (if there are any) and remove any other stuff on it. Ferrite is partially conductive, and thus is is important to insulate the primary windings from the core. A plastic coil form, some plastic sheet wrapped around it, or some turns of insulating tape will work fine. Although the secondary is naturally insulated from the core, capacitive coupling induces quite a voltage on it. Furthermore, don't try to take apart the flyback, and handle it carefully. The ferrite core is quite brittle, and will surely crack if dropped.

Now wind wind 4-6 turns of thick wire on the core. There is no fixed number and you can experiment yourself. Hold it in place with some glue, and than wrap a few turns of insulation tape over it to prevent any mishaps (such as the secondary HV wire getting to close to it and injecting thousands of volts into the transistor or the power supply). Remember to insulate the ferrite core first

Your flyback should be like the diagram above now.

Next is to make the feedback windings. You can use thinner wire and around 2-4 turns should be okay. This depends on your transistor, and need some adjustments for best performance. Secure it again, and insulate for safety. Remember to use well insulated wires. At high voltages, corona can be seen on the wires! Always insulate everything well. Now your flyback should look something like the diagram shown below.

Your flyback is completed! Now the circuit.

 

The Circuit - 2N3055 version

When you hook up all the components, here's how it will look like:

When running of the circuit, the pins at the bottom of the flyback might spray, and might arc to the core. Insulating them with epoxy (the other pins) helps, since they are not needed anyway. Only the HV wire, and the ground wire is used. It is possible to extract an extremely high voltage from a flyback (perhaps over 40kV) by increasing the primary voltage, secondary insulation breakdown will eventually breakdown. The flyback would be rendered dead!

While operating at lower voltages like from a normal 9V battery (not advisable... the battery gets drained extremely fast), R1 could be replaced with a lower value resistor like 150 Ohms. Flyback secondaries are wound with extremely thin wire, and will not handle high current outputs... up to 10mA might be possible, but the value is usually 1 or a few mA... but then again, you will not know when the secondary is ruined so experiment with higher inputs at your own risk. In most normal cases of operation, the flyback should remain cool even when run at the peak unlike a normal transformer. The transistor will however, get Very Hot if you push it, and will probably burn much before your flyback transformer does.

Anyhow, 200 - 250 Ohms will operate the circuit as low as 6V without any problem. The power consumption on R2 (27 Ohms) increases as the input voltage rises. Current inducted on the feedback winding uses R2 to reach ground and might get warm too. Check the temperature and get a higher wattage resistor if necessary, however, they do remain quite cool. The transistor on the other hand does get very hot! It is advisable to mount it on a huge heatsink! Of course the 2N3055 transistor can be replaced with another similar transistor of a high power rating.

Finally, when everything is wired out, carefully bring the HV output (usually a fat red wire with a suction cup thing on the end) towards the bottom of the flyback (where all the pins are). The one which the HV arcs to like mad is ground. If there is a lot of arcing at the bottom, the output might be reversed (i.e. the HV wire is ground). In this case, do the same and find the other pin and ground it. This will solve the problem.

Components you need:

1 2N3055 NPN transistor (get more in case they blow)
1 Large heat sink for the transistor. (Really large)
1 240 Ohms, 5W resistor.
1 27 Ohms 1W resistor.
Flyback, hookup wire, solder, soldering iron, etc...
And a good power supply (6-24VDC capable of at least a few amps)

Updates! 16 Mar 04

I was not able to construct this circuit due to the lack of a good power supply unit... however I have recently acquired a 34A 12VDC power supply unit! (That's 408W of power!) The circuit is up and running.

Here is a photo of my current setup. It's free standing and messy, but it works. I'll mount it in a nice box when all the fine tuning has been done. I am using a 12VDC switch mode power supply capable of supplying 34A! A car battery or a Lead acid battery would work too (and of course be more portable). The power supply must be capable of supplying around 3 - 10A... this would depend on the resistor values and of course the voltage. Remember to place a large DC filter capacitor between the + and - of the power supply if you are using some expensive power supply unit. The filter cap will smooth out all the HV spikes and nonsense coming back. Ideally, I should be using more, perhaps 50,000uF of capacitance.. the largest caps I have now are 4700uF each... so total capacitance I am using is almost 10000uF... I am planning to get a 50000uF cap soon though.

I am using a 2N3055 power transistor... it's cheap and easy to find, though not powerful enough for large power inputs. The resistors and everything else don't get too hot, but the transistor DOES. It becomes Very hot very quickly even with my heat sink in place. The heat sink will be upgraded to a larger one.

When everything is completed and working, there would be a small purple arc between the two terminals. The arc produces a hissing sound and is associated with its frequency. As the arc is drawn, it develops into a high pitched hiss and slowly increase in frequency until it becomes ultrasonic (above 20,000hz) and it becomes quiet. I hooked up a small flyback from a modern tv, and it starts an arc at around 1.5cm. As a rough guide to calculate the voltage, it would be about 1.1kV per mm.

If it is not working, most probably the transistor has malfunctioned, of the flyback secondary is ruined... (shorted out). Check if the transistor is drawing current, and feel the flyback secondary. If it is warm (shouldn't be) the secondary is probably ruined. You might also want to check the windings and see if you didn't connect them wrongly.

More Updates! 7th June 04

The two large 4700uF caps have been replaced by a much smaller 62,000uF 40V capacitor bank to filter the HV spikes. The heat sink has also been upgraded to a huge one and the transistor is much cooler. I noticed the resistors were starting to get quite hot so I'll be replacing them with 5 or 10W resistors just to make sure they don't blow. (My 1W resistor is blackening..) Once everything is done, I'll mount it on a board, or in a box.

Pictures coming soon.

 

The Circuit - Halogen Transformer Version

Want to drive a flyback but don't have time to get the components or lacking a power supply? There is a great alternative! This was suggested by mws on the 4hv forum. The photo below is from him.

Parts List:

1. Insulated Wires
2. A Flyback
3. A SMPSU (Switch Mode Power Supply Unit) These are used for low-voltage lighting. The are different from normal iron-cored transformers (which run at 50-60hz and are thus not suitable). These are electronic transformers with lots of components inside.

The SMPSU outputs a high frequency (usually 20kHz), low voltage current that just happens to be perfect for driving a flyback, typically at 20khz. Basically, this is what a good SMPSU would look like. In this case, the 11.5V output will be used. This model supports a hefty 210 watts. All you need for an excellent flyback driver! However, in where I live in, it is difficult to obtain such a SMPSU. So I am currently using an electronic halogen lighting transformer. Try to get the good models (above 70W). Apparently, where I stay, I can't find any shop selling high powered electronic transformers so I am stuck with lousy 50W transformers which blows up if run for extended periods of time.

What do do now?

1. Wind the Primary Coil

You need to make the Primary Coil. Insulate the core with many layers of good insulating tape first. Just wind around 10 turns and tape it all in place. If you experience any problems with the output, you may need to add a few turns to your primary. If there's not enough inductive reactance on your primary, you may be triggering the protection circuit. Most SMPSU have a protection circuit. Anything from 5 to 15 turns will work. Then again, fewer turns would result in a higher voltage output...

2. Connect them up!

Follow the diagram above, and wire it up... and you're done!

3. Locate the HV ground pin

Now all you have to do is locate your high voltage return pin. Simply turn the unit on, and very carefully bring the high voltage output wire down to the pins on the bottom of the flyback. The pin that it arcs to like mad is the pin you're looking for. You'll want to attach a length of wire to that pin in order to keep it from melting into nothing.

4. You're done!

It's completed! Your ultra simple flyback driver which is easy to build and use!

 


 

Testing and Results

1st September 2004 - Testing using a non rectified flyback driven by a 50W halogen light transformer. (Circuit 2)

Here is my ultra simple setup! Due to lack of a good Power Supply for the single transistor circuit, I am using a lousy Electronic Halogen Lighting transformer. I will be using the good old flyback (white one) for the experiments. Also, remember: never, let the HV lead or the flyback itself get close to any of the primary side components.  *Updated.. I have fixed together a new single transistor circuit.

  

Above you can see a pictures of the flyback operating. The output voltage is close to 20+kilovolts, which is enough to ionize the air without any ground nearby, as can be seen. The corona extends up to .5cm into the air, and once struck the arc can be pulled up to little over 2cm. It makes a loud hissing sound. In this 1/2 second exposure, the electrical arcs can be seen arcing to ground. The rightmost picture is a 1/42 second exposure with flash. It's a bright HOT arc! The metal electrode is currently red hot and ready to melt. Lots of sparks.

Finally, some nice arc pictures through xenon tubes.

 

Updates 16th Mar 04

Due to my latest acquisition of a 408W 12V power supply unit, I am able to carry out the more powerful single transistor driver experiments. As expected, there was a significant improvement over the 50W lightning transformer driver. The arcs look different (less lightning like) and have a characteristic hissing sound associated with its frequency. A much higher voltage is obtained and the arcs can be drawn longer as well.

It is more powerful and much higher voltages can be obtained. I am currently using the smaller cylindrical type ('modern') flybacks. I got it for $5 at a TV repair shop, and its supposedly used in small black and white televisions.

The output cable is rated 20kVDC only, compared to the 40kVDC cable from my bigger flyback, from a large colour TV. However, with 5 turns on the primary, the smaller flyback produces longer, hotter and more powerful arcs... and of course a higher voltage, than the bigger flyback...  I am very happy with the performance of this small flyback. It is small and reliable. I might try getting another similar transformer and winding it in an anti-parallel configuration for higher voltage, but not just yet.

As can be seen from the picture, I wound 5 turns as the primary, and 3 turns as the feedback. I might change the primary to 4 turns to get a higher voltage though... anyhow, the flyback works wonderfully and produces nice hissing purple arcs.  Now the photos :-)

This is a xenon flash tube from a disposable camera. You can see the purple arcs from the air, as well as the interesting white arc patterns in the tube. The tube gets hot quite fast obviously... I learnt it the hot way...

Another lovely photograph of the arcs inside the xenon flash tube. Both air and xenon arcs are clearly visible.

Arcs of the flyback. It is difficult to focus accurately... meanwhile, this photo should do. The arcs are much more purple in reality.

 

Flyback Videos

It is a must to view the flyback videos. Although it's big, it's worth the wait!

Download the Loneoceans Flyback Experiment video 1 now! flyback.wmv (2.78Mb. Requires Windows MediaPlayer)
(Left click and select 'save target as' to your hard disk)

Video Explanation:
The video is in 3 parts.

In the first part, you can see electrical arcing between the two electrodes. That's a 2cm arc. Almost 30,000 volts and can be drawn up to 4cm long. The second part is a close up of the arcs MELTING the electrodes. The third one is an overview. MUST see! The flyback used is the fat white one, and is powered by a 50W halogen light transformer.

More Experiments

Now you have this circuit running, and you have played with it's beautiful arcs, maybe fried a few bugs or cooked a grape, and burned some paper, and you wonder what it can be really used for... Well, the sky is the limit! You can start off by adding a full wave rectifier to make the output DC, which can than be used to power ion motors (729KB), charge capacitors, etc. (or just use a modern rectified flyback)
 
 The non-rectified flyback can be used to power Jacob's ladders, a small Tesla Coil, ion engines, and much, much more... With a cascade, very high outputs can be obtained. But first, make sure to check my plasma globe page to see an awesome use for this device! Otherwise, look below to see my flyback powered Jacob's ladder!

Jacob's Ladder

What is a Jacob's Ladder?

A Jacob's Ladder is the type of high voltage "climbing arc" display seen in many old Sci-Fi movies. Jacob's Ladder come in all shapes, styles, and sizes. So how does it work? The simple explanation is that an arc starts at the bottom and due to the fact that hot air rises, tends to move up the diverging rods until they are too far apart for the voltage provided by the power source. Once this arc is struck the current in the arc will actually increase to the transformer's limit.

Normally the transformer would try to bring the voltage down as current increased. But just above the arc exists a path that the transformer can easily maintain and which in fact will lower its current.  At the top of course we are not only at the upper limit of the transformer but it is also where the current is very low and so the arc breaks apart only to re-ignite down below.

However, there are some dangers. The Electrical discharges in air are also a producer of ozone which may be a health hazard. They also can produce significant Radio Frequency Interference (RFI). Also note that the rods get very hot! Always allow them to cool down before adjustments.

Here you can see my Jacob's Ladder setup.

It's two stiff wires bent and stuck on a plastic box (base)

The red wire connects one end to the HV lead of the flyback and the white one is connected to ground. As you can see, it's really small, simple and easy to make. I did the whole set up in less than a minute.

The background is a black file so the arcs can seen more easily.

 

First light!

 Nice, HOT bright arcs form. Not bad at all! Here you can see it starting from the bottom.

(Apparently, my measly flyback with a pathetic power supply can't generate large arcs, also, the bottom wires were too close and it kept re-igniting before reaching the top.)

 ... after some simple adjustments...

 


 MUCH better!

Here in a 1sec exposure, you can see the arcs rising up towards the top and extinguishing. After continuous use, the smell of ozone becomes apparent and the wires get really really hot.

By coating wires with salt, bright yellow arcs form  instead of the orange, fiery-like arcs you can see here. Using other salts also yield different colours.

 

Here is an short sequence animated GIF of the arc going up the ladder. (400+kb)

This is basically a diagram of how I wired everything up. It's very simple actually. I've tried for both AC and DC and they both work fine.

The Ion Motor

16 Mar 04

*This will only work for DC, which makes this an extremely useful toy to make if you have a DC flyback!

Here you can see a simple diagram of the construction of a ion motor. The stand the the wire (yellow) are conductive. Bend a wire as shown in the diagram. The wire balances on top of the stand, with the tips pointing in different directions. When a high voltage is applied, there will be a hissing sound and ions will start to spray off the sharp end of the wires. This propels the wire in a circle and keeps spinning. The speed can be amazingly quite fast!

Click here to download a 857kb, 30 second video on the ion motor.

 


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(c) Gao Guangyan 2011
Contact: loneoceans [at] gmail [dot] com

 
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