Note: This project deals with high voltage and is inherently dangerous. I’ve built everything I describe on this page – and it works well for me – but I take no responsibility for your actions. If you decide you are interested in high voltage experiments PLEASE be careful and do so at your own risk.
This is part one of a two part article. On this page I am going to show you how to build a simple flyback transformer driver to generate very high voltages. I had to experiment a lot when I first tried this, so I hope to provide enough detail that anyone reading this can successfully generate a high voltage arc on their first try.
In the second part of the article I will show you how to modulate the signal being sent to the control circuitry. Connecting an audio signal to the control input allows you to reproduce those audio frequencies at the high voltage output of the transformer. Using this method, you can use your high voltage arc as a “plasma speaker” or a “singing arc” – with sound originating from the arc of electricity.
Part 1: Choosing a Flyback
The flyback transformer is the most important part of this circuit. Unfortunately, it is also the most complex – and usually undocumented – component. If you know what to look for, a flyback transformer is easy to find and incorporate into your design.
Flyback transformers are used to generate the high voltage necessary to operate older televisions and CRT monitors. They transform a low-medium voltage AC input and into an output of many thousands of volts. Most flyback transformers are designed to operate best at a specific frequency. For instance, the flyback transformers used to display NTSC television signals were designed to operate at ~15,750hz. An interesting effect of this operating frequency is the high pitched “whine” associated with older television sets.
There are two types of flyback transformers: AC and DC. I recommend using a DC (modern) flyback transformer because they often have a voltage multiplier built in. This means you will probably get a larger arc out of a DC flyback than you would if you used the equivalent circuitry to drive an AC flyback.
Luckily, DC flyback transformers seem to be more available anyway. I bought mine on Ebay for cheap, but if you are in a hurry and want to find one locally you should be able to remove one from a CRT monitor or television. You’ll know you have a DC, rather than an AC transformer based on the appearance. DC flybacks are usually black with one or two adjustment knobs on the side. They have a long, highly insulated, wire (usually red) coming from the top that attaches to the tube of the screen. They usually also have numerous pins along the bottom surrounded by epoxy.
Part 2 – Winding the Primary
You have two options to supply the input voltage – you can use the primary winding already in place or wind your own. Winding your own primary is usually a better option because you have complete control over the number of turns. It may also be easier to wind your own primary than to determine the pinout for the built-in primary.
Winding your own primary is easy. Find the location of the current primary – it is the smaller core segment attached to the main body of the flyback transformer. At this point your transformer will likely have the primary wound around this segment already. Note the direction the current primary is wrapped around the core and remove it. Now find some thick single-stranded copper wire to wrap the new primary. Carefully wrap a few loops around the core in the same direction as the original primary. These should be fairly tightly spaced but the turns should not cross each other. When you are finished, wrap the turns tightly with electrical tape.
Note: In the above picture I have stranded speaker wire attached to the primary of the flyback. This is not the wire I used to wrap the primary.
You will need to experiment to determine an optimal amount of primary turns. The output voltage increases according to the ratio between the primary and secondary windings — therefore the fewer windings you have on the primary winding the higher output voltage you should expect. At some point this correlation breaks down. I recommend starting with 10-12 turns on your primary and experimenting with different values after you get everything else working. I currently have 8 turns on my primary.
Part 3 – Gather up the Parts
What you will need:
Breadboard – I recommend building this circuit using a bread board first. The frequencies involved in this design are not so high as to run into any problems with capacitance between the traces of the breadboard. In part two of this article I’ll share a circuit board design for the plasma speaker which uses many of the parts from this design — so you’ll probably want to be able to re-use these parts.
Power Mosfet – SSH222N50A – This is the workhorse of the circuit. Mosfets are essentially voltage-controlled switches — and this one is a BIG one designed for a lot of power. I chose this one in particular because it is rated for peaks of 500v across its output pins and it can handle up to 22amps. Also, it is a very efficient mosfet with an on-state resistance of 0.25ohms. This will be connected directly to the primary coil of the flyback transformer. Mosfets are very fragile components — I recommend buying more than one in case one fails you during development.
Mosfet Driver – TC4424 – I chose to use a mosfet driver IC rather than transistors to drive this mosfet. This simplifies the design and provides a small degree of isolation between the high voltage components and the rest of the circuit. The TC4424 driver is designed to rapidly alter the state of a mosfet and has a wide supply voltage range (4.5-18v). In the future I might try building the driver with push-pull transistors, but I’ll be surprised if they increase the performance over the TC4424. These are also a little fragile without proper treatment. I recommend getting a few of these if you can. Microchip offers free samples to students.
Oscillator – LM555 – This circuit needs oscillation to get any kind of effect from the flyback transformer. You can choose any component you’d like to provide this oscillation. A 555 timer simple and works well with the other components — the TC4424 is enabled by any signal from 2.4v to the positive rail. So you can drive the TC4424 with a “logic level high” of 10v or more from the timer. You can run the LM555 at the same voltage as your TC4424 and using a potentiometer you can adjust its output frequency.
Power Supply #1 – 10-14v, low power – This power supply will be used to drive the 555 timer, TC4424, and turn the mosfet on and off. It should be at least 10v to ensure the power mosfet is fully turned on.
Power Supply #2 – high voltage, high power – This power supply is used exclusively to drive the flyback transformer. Try to find a moderately high voltage power supply for this that is capable of sourcing at least 1-2amps. For all of the arcs pictured on this page I used my bench power supply which was capable of providing 25v at about 1.5 amps. In my “plasma speaker” I had to make my own power supply capable of sourcing 60v at 2-3amp. Interestingly, high voltage isn’t required to operate this circuit. I’ve hooked up a 9v battery and gotten 1-2mm sparks about of the flyback.
Note: It is possible to run both parts of this circuit from the same power supply, but I don’t recommend it. The highest voltage you can run the 555 timer at is 16v. This voltage is far too low to get the most out of your flyback. If you decide to use the same power supply, I recommend puting some capacitors across the power rails near the 555 timer and TC4424 to smooth out any spikes created by the mosfet switching.
Heatsink – Despite its efficient design, the mosfet will produce a significant amount of heat. Find some metal to attach to the body of the mosfet to dissipate the heat. The heatsink I use (above) is actually NOT large enough to run my plasma speaker indefinitely – I have to turn the speaker off after a few minutes of operation.
Assorted Resistors and Capacitors – Check the schematics for more information about values.
Part 4 – Assembly
Note: Assemble everything, but DO NOT turn on the high-power supply yet!
Use the above schematic to assemble the flyback driver on your breadboard. In addition to the previously mentioned components you will need:
(1) 5k Potentiometer
(2) 1k Resistors
(1) 10 nF Capacitor
(2) 0.1 uF Capacitor (essential!)
In this circuit the 555 timer is acting as an astable oscillator. Using the potentiometer between pins 6 and 7 of the 555 timer you can adjust the frequency of oscillation from 11-48kHz. If you cannot find a potentiometer, you can try replacing the resistors between pins 6 and 7 of the timer with a single 3k resistor. This will lock the frequency at about 20kHz.
If you have an oscilloscope, I recommend testing pin three of the timer after you have everything assembled. You should see a square wave of the appropriate frequency on this pin. You may also want to check pin 7 of the TC4424 chip to make sure the signal is propagating through the chip.
Make sure to use the decoupling (0.1uF) capacitors in the circuit. The TC4424 probably won’t operate and can even be damaged without this capacitor.
Part 5 – Turn it On, Verify it Works, and Determine HV-
When you turn on the circuit the high voltage from the flyback will appear between the red tube on the top (HV+) and a single pin along the bottom (HV-). The easiest way to determine which pin is connected to HV- is to turn it on and observe it. First, cut the “suction cup” from the end of the red wire and strip a small amount of insulation off the end. Use electrical tape to attach the end of the red wire to the end of a long wooden dowel. You will use this as a “wand” to point red wire at each of the pins along the bottom of the flyback transformer.
If you can – you should turn down your high-power supply at this point.
Turn on both of the power supplies and see what happens. If you don’t get any arc between the red wire and the bottom pins turn everything off and switch the wires of the primary winding on your breadboard. Next time you turn on the power supplies you should get a substantial arc between the HV- pin and the HV+ wire.
Now turn everything off and solder a wire to the HV- pin. Once you have HV- and HV+ wires coming out of the flyback cover the ENTIRE thing with electrical tape to prevent shorts. This is what my flyback looked like when I was done:
Part 6 – Enjoy
Now have fun creating giant sparks of electricity! If you are dissapointed with the sparks you get out of your transformer you can either tune it using the potentiometer or add a larger power supply. I’ve gotten arcs about 3-4 inches long using only 30-35 volts. Please be careful, but have fun! Let me know if you have any questions or if you know of any ways I can improve my design!
When you get bored with high votlage arcs, stay tuned for the 2nd part of this article: Building a plasma speaker. I’ll show you how to modify the current circuit so that the high voltage arc creates music. This is a video of my plasma speaker:
Here are some pictures of sparks I’ve created:
These sparks are about 2.5 inches apart.
Short time-lapse of my jacob’s ladder.
This was done on my workbench with only about 15v input voltage.