Electronics Projects Index

After transitioning to WordPress, I started writing up my newer projects as ‘blog posts’ rather than ‘pages’. Please find below a list of links to every electronics project related blog post:

Comments (38)

  1. tobias says:

    Scott
    Very good work you did here! The IRF250 you got is way better then my already very expensive in Brazil 540. And very clean PCB. Mine home-made board blew some traces so…

    About the MOV: I think you really don’t need them if the system is well tunned. The problem is that while you are tuning it the FETs blown one after another… If it is tunned a 110 V MOV should not heat too much. Same to the snubber resistors. Mine smoke several times.. but at least the mosfet was happy.

    Do you have a oscilloscope available to tune your system? It helps a lot with frequency modulation!

    Good to know that I on google! hehe
    Best regards and good luck with your project
    Tobias

  2. admin says:

    Thanks very much for all the comments, Tobias. I found your site very helpful in my research. The snubber resistors aren’t getting hot yet, but I do have two 5-watt resistors in parallel, so that’s probably giving some pretty power handling capacity.

    I too have blown many mosfets while working on this project. Most of them were IRF840s or IRF540s. That’s why I decided to try out the IRFP250. The current board I created is actually setup so that either mosfet can be soldered in place.

    I do have an oscilloscope available, but I’ve not yet figured out the procedure for frequency tuning. Any tips you can provide would be helpful.

  3. tobias says:

    This picture shows the voltage on the primary while I was tuning the system:
    http://tobiasmugge.files.wordpress.com/2009/03/p250509_09-55.jpg
    That’s the best I’ve got but can be tuned better.
    Are you using a cap in parallel with the primary on the flyback?
    It’s difficult to choose the value because you have this capacitance, the number of turns on the primary, the frequency and the dead-time to adjust.
    Fix the dead-time around 40% and start from there. Change capacitance, search for the best frequency. The right one is when the arc is not that hot but consistent and the current consumption is low. You want to work something between 60 and 100 kHz. More frequency equal better sound.
    If the freq is too high or to low just change capacitance or turns. But stay around 12 turns for 30 V. And start tuning with a low voltage, like 12 V.
    To fine-tune change the freq and dead-time until the wave of the voltage on primary reaches the ‘smoothest’ point.
    Yes, it takes a loot of time!

  4. admin says:

    Hello Tobias, I don’t have a capacitor in parallel yet. Are you just doing that for tuning, or for general operation as well?

    I haven’t got the scope out yet, but I was playing with the circuit tonight and tuned it to what sounded best. I’m now getting somewhere around 4 amps at 30 volts. I still ended up burning out the mosfet after a while of continuous operation (I’m thinking the CPU fan I have is not adequate enough for extended operation).

    There’s something a little weird with starting the arc at my current tuning. To “start” the arc, I have to close the gap down to about 3/4″. Once it’s started arcing, I can easily open it to 2-2.5 inches or more.

    Got the oscilloscope out and made some measurements…. they’ve been added to the post. Not entirely sure what I’m looking for at this point. I haven’t added a cap to the primary yet.

  5. tobias says:

    I used Richie’s site as one of my references. From there Ive got the snubber design. You want to reach the Vc waveform:
    http://www.richieburnett.co.uk/temp/flyback.gif

    Mine is pretty close as you can see on the picture of my site.
    That waveform gives me a 1″ starting arc. I did not tried to stretch it up.

    With 30 V, only ~2A. Depending on the modulation, 2.6A. And no burning fets.
    The cap stays there for operation!

    Best luck

  6. admin says:

    Very interesting results. I started playing with capacitors. The first few I tried (2.2uf and 1uf respectively) increased the amperage significantly. However, when I got to the lower values in the parts bin, that’s where things got interesting. An 0.047uf/250V cap reduced the current draw by about an amp, but the little cap started to get quite hot. I started playing with some 0.01uf/1.6KV caps and found that with two of them in parallel I was able to increase the frequency to about 120Khz, dropping the current draw to about 2 amps. Four of them in parallel drops the current to around 1.6A, but I’m tapped out as far as I can go on the pots for lowering the frequency.

    I finally have a COOL running plasma speaker that sounds pretty good. As far as I can tell no more fried mosfets or hot MOVs.

    Time to start work on revision 2.1 of the driver board…

  7. tobias says:

    Very good results!
    Good to know that you did it.
    Are you in USA? It’s quite easy to you to buy FKP caps out there.. Those does not get hot.
    Maybe we can help each other designing this rev2 board? Tell me how many bucks it costs to make a industrial board there.. Here in brazil it’s like $60.. a little fortune! hehehe
    A tip: the PWM signal circuit cant be close to the power section of the board. Take a look on yours. It’s pretty close. This lead to noise…

  8. admin says:

    Yes, I’m in the US. Some of the capacitors I have laying around are Wima caps (from Mouser, I think). I’m not sure about these particular 0.01uf/1600v ones though. I’ll have to double-check where they came from.

    Generally I get the pc-board from batchpcb. The cost to make the last board was only about $17, but one has to add $15 shipping and handling to that. I usually batch up several different projects together so I can save on the shipping and handling fees, so it’ll probably be a while before I submit the next plasma revision. The new design is already slightly bigger, and batchpcb charges by the square inch, so it’ll cost a bit more. I have moved some parts around a little bit. In particular, the op-amp is no longer next to the high power section and has been moved to the other side of the TL494 where the rest of the low power stuff is. I’ll see if I can post an image of the revision when I get a chance.

    I’m thinking of modifying the design to a push-pull design (or at least have the option of doing it). I don’t think this would be hard to do — it’s basically duplicating everything on pin #10 of the TL494, sticking it on pin #9, and switching the output control jumper. Then we put a center-tapped coil on the flyback. I’m assuming I would duplicate the snubber as well. This could all end up a much larger board which is a little unfortunate. I might try some experiments first to see how much better the push-pull design works.

  9. tobias says:

    In my next plasma speaker project I would like to get rid of that 4429 IC to try a GDT.
    494 -> BC transistor -> GDT -> FET
    And go for bigger FETs as you did.
    The problem is that here in Brazil anything unusual is too hard or to expensive to get. Or even both. The 4429 is both.

    Are you trying to do a halfbridge design?

  10. admin says:

    No, I’m going to try experimenting with a push-pull design… If I understand correctly, this is different that a half-bridge. Whereas the half-bridge is switching a single primary between +V and -V, a push-pull uses a center tapped coil, with +V at the center and alternately switches either end to -V. The design was suggested to me in one of the comments to my youtube video, so I’m going to give it a shot. Of course, my knowledge of switching supplies is very limited, so I may not be understanding correctly. 🙂

    Anyhow, I sat down to look at my schematics tonight, and before I knew what happened, I had a design ready and sent off to batchpcb. Should have the new board in a couple of weeks (batchpcb is rather slow). It’s easy to get carried away when one sits down with the schematic software…

    As far as the TC4429s, I got them from digikey at about $1.72 each. Seems like I shopped around to get a good price on them, but unfortunately I only grabbed a limited quantity (didn’t know at the time my summer free time was going to be dominated by plasma speaker projects!).

  11. Peter (petedog444) says:

    I thought I would write you and tell you how much I appreciate you sharing you experience and your design. Few people on the internet have shared a complete Schematic. I look forward to seeing a video of you new push pull design.

    I hope I can purchase a PCB from you when you are satisfied with your design.

    From your comments to Tobias your explanation of how the a push pull works sounds correct to me. I would very much like to follow along with you during your design adventure. I am no expert but I am well read and I have resources that may be helpful along the way.
    Feel Free To E-Mail me
    Good Luck.

  12. Peter (petedog444) says:

    Could you explain you preference of FM over PWM, please?

  13. admin says:

    Thanks for the comments, Peter, and thanks for setting me in the direction of the push-pull design. I’m looking forward to seeing how it compares to the current design. We should know in about 2.5 weeks! 🙂

    As far as the Pc-boards, I use batchpcb, and they have a marketplace. I’ve held off on listing them publicly so far until the design(s) are finalized, but once they’re ready I’ll definitely list them so that people can order a board. Processing from batchpcb takes a little while, but getting a quality double-sided silkscreened and solder-masked board is worth the wait.

    As far as FM vs PWM, I thought the FM sounded better. The board is designed to support either method (in fact, you can even use both at the same time; it would be interesting to feed two different audio sources and see what happens). The latest revision will have the option of jumpering the op-amp to either. As far as why the op-amp is there, it came from tobias’ design…

    Thanks again for the comments!

  14. tobias says:

    You need that op-amp to have a high impedance audio in. It works together with the capacitor that follows. This last one changes the reference from 0 V to 6 V to source the TL494. Connecting a capacitor this way ensures that no DC voltage differential will be created between the op-amp and the tl494. Only pulses pass throw the cap.
    When you read on the net that people blew some audio players off experimenting with plasma speakers that’s because they did not use a high impedance audio in =)

  15. Zsombor says:

    The finest plasma speaker circuit I’ve ever seen. If possible, can you please also publish your PCB design?

  16. admin says:

    I was planning on holding off putting the PCB pattern up (and the link to manufactured boards at batchpcb) until the next revision is done as there are a few important changes I made. I definitely will do so when the new boards arrive, thanks for the comment!

  17. Zsombor says:

    Thank you, I’m looking forward to it. My biggest problem is FETs’ heat dissipation; I’m thinking about how to absolutely avoid linear mode, maybe with an additional switching-mode FET driver. This is only a plan, I haven’t tried that yet.

  18. Peter says:

    I can’t wait to see your new board. The suspense is killing me. I would really like to know what you thoughts are on the Push Pull system. I already started ordering the parts for your board when you make it publicly available. May be a quick up date would be nice. Thanks and keep up the good work!

  19. yoni says:

    great info! very impressive work!

  20. Peter says:

    I and every one else following you would appreciate an up date on how the new push pull boards are going. Thanks. 🙂

  21. Justin says:

    Any updates to the schematic? I have been looking over the parts, and getting setup to make one for myself. I have also been wondering if the input audio can raise and lower the volume of the “speaker”?

  22. Jim Beam says:

    Can’t wait to see the next revision! Out of all the system’s I’ve looked at this seems one of the best designed

  23. Peter says:

    How is it going. Are you blasting some matalica on your new plasma speaker yet. LOL . An up date on you web site once in a while would be nice. Thanks and keep up the good work.
    Peter

  24. Peter H says:

    Do you think a 163 volt clamp 80 volt DC rated MOV will work. I am building my own prototype and need advice on picking a MOV. Any Advice would be help full. Thanks.

  25. William says:

    Hello ther thank you for your post, i have been searching for plasma speaker and i did like very much yours, i wounder if you mind to send me the list of materials necessarie to do the entire build. Thank you so much

  26. Luke says:

    Ty for the prints, i was searching for a good FM build and these fit the bill brilliantly. http://hv-labs.xf.cz/images/singarc/budic-mustek.png
    I plan on implementing push pull like this soon.

  27. Josh says:

    You did a great job, and just like you , I have been working on plasma speakers for 2-3 years now (ever since I started College). I have been looking at Tobias’ design for quite some time and have found it to be one of the best designs as far as run time goes. But my plasma speakers generaly fail miserably for unknown reasons like my lastest one. One day I test it and it worked beautifully, nice arc with clear sound and no heating of the mosfet or other components. It was like a dream come true from my other designs which blew mosfets like firecrackers. Well a week later after it ran just fine it decided not to work anymore – didn’t touch it- it just didn’t work anymore. It tries to draw over 5amps from the supply and then I thought I wonder if its like what u were saying about the 1st technique in audio modulating the flyback by injecting the audio into the RC timing section and not the dead-time. I really just think my plasma speakers have a grudge on me or something… Other than that every component is fine and functioning normally – leaves me stumped and stupefied. Have you come across this problem were it would just not work anymore for no reason? I can tell you another interesting thing is that my low power side has a separate ground then my high power side and when connecting them both together I get a really week arc and the mosfet gets hot quick, another wierd thing.

  28. tobias says:

    Any luck with the new design?
    Thanks for sharing the high voltage PSU design!

  29. admin says:

    I haven’t had a chance to try it out yet… work has been keeping me busy 🙁

  30. Peter H says:

    Do you plan on continuing your testing and design of your plasma speaker in the near future?

  31. chrismec says:

    I am interested to hear about the new design! Been waiting for months. I like your wordpress template too ; )

  32. admin says:

    Yes, I’ve had some more free time lately, so I think I might be able to get some more plasma speaker work done!

  33. Peter H says:

    Still wondering how the Plasma Speaker Project is goning?

  34. Peter H says:

    Thank you for the update. Were you able get a longer ark with the push pull than with the half wave? May be you could put up a quick up date video. I would Really appreciate it. I had a printed circuit board made based on Tobias and your design. It includes the Push pull also. I will let you know how it goes when I get it up and running. Best wishes.

  35. Jack says:

    very nice project! i’ve also found the instructables website already and was planning to build one as well. I guess you took a decision with the higher voltage varistor, they seem suitable only for limited pulse loads: http://www.resistorguide.com/varistor/

  36. Steve says:

    This is a very nice project, and has my interest piqued, but there are some aspects that are just painful to watch… If I may…

    1, why are you using MOSFET driver chips for this? My gut instinct without looking up the FETs you’re using is that the Vgs requirement is excessive. There are several MOSFETs that are better suited for the switching here, and have a much lower Vgs rating. IRFZ44N for example – can be saturated at around 6V. They also have a much better current handling ability, and if for added insurance against popped transistors, get one that is avalanche rated. I drive flybacks experimentally all the time with no snubber whatsoever, no problem. I include them in printed versions of my projects for added insurance, but a suitable transistor can handle what a flyback can dish up. The 494 has a more than adequately qualified totem pole output that can drive these transistors directly.

    2, Snubbing reduces the effectiveness of a flyback transformers operation. You WANT rapid collapse of the field in the core to get maximum output efficiency. Snubbing steals some of this energy away from the system, reducing the output, requiring more drive.

    3, Try going more with very low duty cycle to establish your arc. This can be difficult to do, as you’ve discovered. Using the caps in parallel with the primary can help, but just as with the snubbers, this method can reduce efficiency. The mechanism is different however, involving dv/dt rather than raw “theft” of the energy. Low duty cycles will help with this, as it will operate more as a class C system than the brute force method that is evident in the scope traces. Less is more in this case.

    Last but not least, PWM is your friend here. Tune the chip to the transformer and let resonance do the work! More duty cycle means more current in the arc, which means more heat, which means more air displacement. Let the transformer do the work, not your power supply and MOSFET. You’ll be able to get more SPL out of it, and the transistor will run much cooler.

    Email me if you have any questions.

    Steve

  37. Craig says:

    Great site.

    I just built a similar plasma speaker using the same TL494 chip and a MOSFET driver. Works great apart the FET gets very hot even with a big heat sink. Can someone explain why the output of the MOSFET driver is via a 470R and not directly connected to the MOSFET. Would the MOSFET switch quicker if connected directly to the driver chip?

  38. Manuel says:

    This is a very interesting project, I would like to build one as well. I’m not expert with electronics stuff but I think I can manage it easily, (high voltage, soldering etc not an issue). I have some difficulties to understand the schematic for the version 1.0 of your board. I kindly ask you if you can help me also P.M. with a “foolproof” schematics of the complete board. I would Really appreciate it. Best wishes.

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