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Registered Member #3429
Joined: Sun Nov 21 2010, 02:04AM
Location: Minnesota, USA
Posts: 288
I've been building electronic gagets and projects since before many of you guys on 4hv were born, but this is my very first project using MOSFETS (I think it's about time! LOL). This is a flyback driver that has screw type binding posts that allow quick connect and disconnect of the flyback primary leads, and that way I can quickly go through a large box of flybacks while testing their output voltage and resonant frequency. Currently, the circuit can only drive a flyback in CW mode, but I am planning on designing a modulator circuit in order to use it as a "Plasma Tweeter". I'll update this thread if/when I have a working prototype.
The circuit was designed by Steve Ward, and here is his schematic diagram. I made a few minor modifications, but the circuit is basically the same. The differences are: 1. I used IRFP460 MOSFETS instead of IRFP260. 2. Instead of a 2N3055 as the series pass transistor in the variable power supply, I used a MJ413 power transistor which can handle much higher voltage and current. 3. I added a small DC fan which helps to cool the heatsinks on the driver board. 4. I added a 2-pin jumper which can add another capacitor in the timing circuit for lower frequency operation.
Like most other guys who have experienced having to replace blown transistors that were soldered to a PC board, I didn't want to have to do that in the likely event that I would blow out the MOSFETS by driving them too hard, so I decided to use in-line screw terminals as sockets for the MOSFETS. Now replacing them will be a piece of cake!
Here are some pictures of my completed project:
Update July 20, 2011 -- After some expirimenting with winding a primary coil on one of my flybacks, I am getting some good arcs that are approximately 25mm to 30mm in length, and the arc gets very hot when I tune the frequency just right. It gets the tips of 1/8 inch welding electrodes red hot! After about 30 seconds of continuous arcing, the pass transistor in the power supply gets very warm, almost to the point where it's too hot to touch. I need to mount a small fan on the power supply board like I did for the driver board.
I'll post a video of the arcs some time later today or tomorrow.
Update July 21, 2011 -- Here is my YouTube video showing both an AC and a DC arc:
Update July 27, 2011 -- I made some major changes to this project. For one, I got rid of the wimpy variable (0~30VDC) power supply and now I'm using a Variac that's powered right off the Mains, and the output voltage is rectified by a heavy duty bridge, feeding a big honkin' filter cap. Now I can make some decent long, hot arcs with every flyback that I've tested with it. This new design gives me 0 ~ 200VDC at "many" amps (I'm not sure yet how much current it's capable of sourcing, but I'm careful to not blow up the mosfets!)
I mounted all the components on an old steel chassis that was orinally used as a pneumatic station (it originally had a pressure regulator and tool oiler mounted on it).
I did not bother to draw a shematic diagram of the variable DC supply because it's so simple. Here are a couple of pictures of the modified project: (I had to link to pictures on my own web site because 4hv does not let me add pictures directly from my computer when "editing" an original post).
Registered Member #1643
Joined: Mon Aug 18 2008, 06:10PM
Location:
Posts: 1039
Lookin good, first time ive seen angle sockets used for mosfets, I'm always use to right-angle not ~45, hopefully things perform well and you get nice size hot arcs!
Registered Member #3429
Joined: Sun Nov 21 2010, 02:04AM
Location: Minnesota, USA
Posts: 288
Patrick wrote ...
can something else be used to gain rapid switching other than a gate drive IC? I dont have any at the moment.
Maybe an OP-amp?
Patrick - I'm sure that there are other ways to drive the gates rather than with a gate drive IC, but since this was my first project using mosfets, I didn't want to deviate too much from the original design. You may be able to drive the gate drive transformer directly from the output pin of the 555, but someone else should confirm that before you try it. I'm a firm believer in simplicity, so if you can get the same or better performance with fewer parts, then that's the way to do it (remember Occam's Razor?).
Other guys - Thanks for your kind and supportive comments. I appreciate feedback, even the constructive negative type!
As for arcs, sure, I could take a picture of a flyback producing an arc, but that's not what this project is all about. So far, the arcs that I've seen with this driver are not very impressive (only about 1 cm long), but it's probably not the fault of the driver, but rather the way I wound the primary coil around the flybacks that I've tested. Anyhow, I'm not in competition with anyone to see who can produce the longest and fattest arc. As I stated in my original post, I plan on using this driver for testing flyback transformers, and ultimately I want to see if I could design and build a plasma speaker which is louder and can handle a wider bandwidth than most other plasma speakers that I've seen and heard on YouTube. I have a couple of ideas for a design, but I'm keeping them "secrect" for now.
Registered Member #3429
Joined: Sun Nov 21 2010, 02:04AM
Location: Minnesota, USA
Posts: 288
Patrick wrote ...
Ill show youmy design too! mine is similar to yours, though I use mine for HV insulation testing. Nice work.
I presume your is just for the old flyback type? the AC ones? will a half bridge work with a modern diode-split type flyback?
I tested it with both DC and open frame AC flybacks, and it works very well with either. Just for fun, I put a 15KV ceramic cap across the output of one DC flyback to make some DC arcs, and they are very loud and impressive when they discharge! I'll include some AC and DC arcs in my video, which I'll try to post in a day or two. For now, I'd better get some X-ray heads repaired before my customers start to call and complain that it's taking too long!
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
Xray wrote ...
I tested it with both DC and open frame AC flybacks, and it works very well with either. Just for fun, I put a 15KV ceramic cap across the output of one DC flyback to make some DC arcs, and they are very loud and impressive when they discharge!
Well thats interesting, I wounder if the primary load is asymetric, due to the HV diode? Well as long as it works, so be it.
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Flyback Transformer Driver and Power Supply
