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120VAC to 240VDC for plasma speaker circuit

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TheBestJohn

Thu Jul 08 2010, 09:16AM

Registered Member #2980 Joined: Thu Jul 08 2010, 08:57AM
Location:
Posts: 3

Hey everyone! My name is John and this is my first post. I have been working on a plasma speaker for about a year now and have had some success with a version that switched a MOSFET on and off "softly" creating a lot of heat and a lot of used up MOSFETS. I am using a TL494 IC circuit and am now undertaking the arduous task of making a circuit with a UCC37322 MOSFET driver to keep my MOSFETs happy and running.

Here's where the real hiccup is. I am using this:

circuit and I live in Canada... 120VAC land. My question is how do I step up the voltage to 240V? I know about bridge rectifiers to convert to DC but its the stepping up to 240 thats got me stumpped. I've been told that this can be modified to run off 120VAC but I have no clue how / know weather or not the size of the arc would be affected.

any help?

EDIT: this is the advice I've been given

-lower voltage higher current transistors (IRF640, IRFP250/260 etc.)
-higher current clamping diodes (at least 10A, might need heatsink, MUR1560 comes to mind)
-less turns on the primary winding (~40?)
-higher value filter capacitor (~1000uF 200V)
-different values of the RC network on the primary (capacitance 1-2nF, resistance ??? <- this will need experimenting, put a single turn around the primary and connect to scope, see which resistance value damps the ringing the best- start with ca. 1k 10W and try higher/lower values)

I assume the clamping diodes are the uf4007s... the only thing I am unsure about is the RC network. or what RC stands for, for that matter.

Coronafix

Thu Jul 08 2010, 10:29AM

Registered Member #160 Joined: Mon Feb 13 2006, 02:07AM
Location: Melbourne, Australia
Posts: 938

I don't see why you can't run it off 120 as is?
If you really want 240V, just use a suitably rated step up transformer before rectification.

MRacerxdl

Thu Jul 08 2010, 11:00AM

Registered Member #989 Joined: Sat Sept 08 2007, 02:15AM
Location: SÃ£o Paulo, Brazil
Posts: 476

Or make it a Full Wave Voltage Doubler, as you have 120VAC

Dr. Dark Current

Thu Jul 08 2010, 03:01PM

Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384

Hi TheBestJohn, I'm "jmartis2" from youtube.
No the clamping diodes are the HER507's.

MRacerxdl's advice about the voltage doubler is also good. So you can decide if you want to power it directly with the different components or build the doubler and use the circuit as-is.

-JM

doctor electrons

Thu Jul 08 2010, 08:45PM

Registered Member #2390 Joined: Sat Sept 26 2009, 02:04PM
Location: Milwaukee Wisconsin
Posts: 381

Welcome John!
There is a few things you can do! Use a suitably sized step up transformer, or backfeed a suitably sized step down transformer.
I actually use a 480v primary to 240v secondary step down backfed with 120 to get 240. Its all about ratio! Just be sure the kva rating
is sufficient to provide the amperage you need. And be sure to use a 2 pole breaker or 2 fuses that you can disconnect at the same time!!!
In the U.S. when i need 240 and a lot of current i just use my panel, using 1 hot from each of the two phases will yield 240 as they are 180 degrees
apart. I use class cc fuses when i do that because the blow curve is 1/4 cycle. Good Luck!

TheBestJohn

Thu Jul 08 2010, 09:53PM

Registered Member #2980 Joined: Thu Jul 08 2010, 08:57AM
Location:
Posts: 3

Hey Dr.Kilovolt! I have to say I am not the least bit surprised to see you here! I think I will go the route of a voltage doubler... I think I may have the proper transformer in a switching PC power supply.

HV Enthusiast

Fri Jul 09 2010, 12:55PM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068

I guess the question is - do you really need that much voltage? 120VAC rectified will give you about 170VDC.

Of course, a voltage doubler will get you to about 340VDC and probably the most economic way to go.

Just keep in mind that if you really increase the power levels, you need to add LOTS of cap to keep the DC voltage clean, otherwise you'll begin to hear "hiss" due to the ripple, even on 3MHz+ coils. Plus, adding lots of cap also creates large peak currents in the rectifier which can premature trip breakers, etc...

TheBestJohn

Sun Jul 11 2010, 01:19PM

Registered Member #2980 Joined: Thu Jul 08 2010, 08:57AM
Location:
Posts: 3

Well I really want to have a nice big arc. with the 170V would that not affect the size of the arc. It would be ideal if I could just use the 120V however I got my TL494 chip out of an old switching power supply and I do believe that it has a transformer in it that will allow me to get the 340V that the schematic was originally looking for.

EDIT: after much deliberations I have decided that I will got with the straight 170V even if it does mean smaller arcs. I think it will give me chance to learn how to use my oscilliscope as well as afford me the chance to learn how to change existing circuits to suit my needs. Also I won't need a transformer to complicate things. already I have learned by reading various materials that your filter caps should be roughly 2X the expected voltage to be safe.

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