The ZVS Flyback Driver
It is probably the most powerful and efficient flyback transformer driver that was fairly recently invented by Vladmiro Mazilli. It uses resonant zero voltage switching (also know as ZVS) to drive the flyback transformer. This means the MOSFET's are designed to switch (on or off) when the voltage across them becomes zero.
Because the MOSFET's switches when there is no voltage across them, it will generate very little heat, the only source of heat is caused by the MOSFET's internal resistance. Unlike the simple 555 timer flyback drivers, The ZVS flyback drivers will allow you to run your flyback transformers for much longer periods of time before the MOSFET's overheat. If you get really good MOSFET's, it might be even possible to run your ZVS flyback driver infinitely! (Or until the circuit is interrupted)
Video of it working!
Step 1: The dangers of the ZVS flyback drivers
Do NOT attempt to do this as your first flyback transformer driver project, I recommend you to start with using simple 555 timer flyback drivers before thinking about building an ZVS driver.
And finally, you are solely responsible for any harm to others or damage or any other problems that a ZVS driver may cause. The ZVS driver should be used for educational and research purpose only.
That is the end of my health and safety rant. :-)
Step 2: Parts
• Flyback transformer
Newer flybacks are recommended as they are very robust. You can use an older flyback for higher current output, however, they are more likely to burn out due to excessive voltage.
• 2x 470Ω 2W resistors
The color code is yellow/purple/brown
• 2x 10KΩ 1/4W resistors
The color code is orange/brown/black
• 2x 12v 1/4W zener diodes
• 2x 400+ volts fast diodes
I used UF4007 diodes.
• 1x inductor
The value is not critical but it should be 47uH to 200uH rated at 10A or more. You can find an inductor from a computer PSU or you can simply make your own, just wrap 20 turns of 16 gauge of enameled wire around a ferrite toroid.
• 1x 0.68uF 250v (or higher) capacitor
This capacitor must be bipolar and must be good quality, such as MKP ot MMC types. NEVER use an electrolytic capacitor, they will blow up. You can test various types of capacitors to see which one suits your ZVS driver well.
• 2x IRFP250 MOSFET's
They are a bit pricey, however, you can use other MOSFET's that has Vds 4x more than the power supply and has the Rds(on) lower than 150mΩ. Unfortunately those MOSFET's are a bit over my budget so I used the IRFP254 MOSFET's instead, not the best, but it is cheaper and it and it should give me good arc results. I also tried using the popular IRF540 MOSFET, however, it gave me very poor results.
• 2x small heatsink
They won't be necessary if you are going to run your ZVS driver lower than 12v.
• Large variable voltage power supply
Now this can cost quite a big chunk of change, you can a computer power supply unit for 12v power source. If you want a higher voltage power supply, then you might want to consider modifying a microwave oven transformer, but this is another project. As I don't have a large power supply so I used six 6v sealed lead acid batteries all in series to gain 36v to power my ZVS driver.
Then finaly the other bits and pieces you may need such as solder, thick wires, etc.
Step 3: Schematics
The "47-200 µH" inductor can be customized to the desired output of the flyback transformer. In general, if you want a higher voltage, the inductor should have an higher value, if you want more current, the inductor should have an lower value. Also, an inductor is a 'must' for the ZVS driver, without it, your ZVS driver may work poorly or not work at all.
Changing the value of the capacitor can also affect the performance depending on the flyback transformer, again, make sure you use good quality capacitor.
Step 4: Construction
Make sure you use thick wire as it will be handling currents up to 10 amps.
When winding the flyback transformer, make sure both wire go the same way.
If you are going to attach both of your MOSFET's on one heatsink, Use mica insulators! Or other types of insulators to isolate the MOSFET's tabs from each other, otherwise your ZVS driver won't work.
Step 5: Power her up and set wires on fire!
You may hear an very high pitched squeal from your ZVS driver, don't worry, that is normal.
What ever you use as your negative terminal, it will get hot, very hot! The arc will melt any thin wire you use into little metal balls and steal will just fly everywhere, which is cool (and dangerous)! If anyone has a good explnation why the negative terminal get so hot and the positive terminal remains fairly cool, I'd like to know.. :-)
Also, in the video, just after the arc burnt a hole into a lightbulb, they was a stream of plasma 'shooting' out of the bulb, like a flame thrower. This is because when the arc got inside the bulb, the gas inside heats up, causing it to expand and escaping through the hole thus creating a "plasma thrower".
Step 6: Modify your ZVS driver for higher performance!
Also, make sure your 3 turn windings are the same direction as the primary, otherwise you will blow the MOSFET's!
Step 7: Going further
For input voltages over 36v:
Change the 470Ω resistor to 1kΩ resistor.
Change the 12v zenner diode to 15v zenner diode.
Increase the number of windings on your flyback transformer.
Increase the value of the inductor.
This should work well for voltages up to 60v before the MOSFET's should be changed as well...
I heard that some people had operated their ZVS driver at voltages over 100, just imagine how massive their arcs must be!
Also, this ZVS driver circuit does not have be used just for the flyback transformer, you can replace it for use a different transformer to charge up your large capacitor banks for coilguns, railguns, etc. It might be even possible to do induction heating with this ZVS driver circuit...