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Plasmasonic II build

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indiana

Wed May 06 2009, 03:19AM

Registered Member #2009 Joined: Tue Mar 03 2009, 07:07PM
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Posts: 43

thanks all, those waveforms were at the gates, unloaded.

i'll connect the fets and see how we do with it powered.

LithiumLord

Wed May 06 2009, 08:54PM

Registered Member #1739 Joined: Fri Oct 03 2008, 10:05AM
Location: Moscow, Russia
Posts: 261

Better not ;) Rig everything up, but do NOT power up the bridge - get the gate traces off each switch first. Only if none of them show the +3Vgs during deadtime (I suspect some probably could as the traces are identical, it's only the polarity that is reversed) you are free to go, otherwise it will be a hell to debug and replace the blown components.

indiana

Fri May 08 2009, 12:15AM

Registered Member #2009 Joined: Tue Mar 03 2009, 07:07PM
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Posts: 43

@lithiumlord:

I think they should be okay... the gates are all identical, just phase shifted. i've put in a photo with both gates.

there's never a point where it goes positive 3V. Just to be safe, I'll get the traces off the switch... how do I do that though? measuring off the switch with the fets connected?

I'll give it a go, and at any rate, i'll be testing it at very low power to start, and building up to full power, checking for heating the whole way along.

Feel pretty good about it now, but better safe than sorry.

HV Enthusiast

Fri May 08 2009, 02:32PM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
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What frequency are you running at? It says 694kHz in the screen shot which is much too high. I wouldn't run over 350kHz.

indiana

Sat May 09 2009, 05:43AM

Registered Member #2009 Joined: Tue Mar 03 2009, 07:07PM
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Posts: 43

I was puzzled by those numbers too. I wondered if it would come down if i tested all four at once. don't have the capacity to do so though...

It was running approx. 350KHz at the test points before the GDT, and when I test one gate alone it gives a reading in the 1.something MHz range. two points together gave me about 700, seemed logical to think all four would come down to the right speed when loaded, considering.

But I was curious about that as well. Does it seem strange to you as well?

...

Sat May 09 2009, 05:52AM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445

At first I thought it was the scope getting confused by the ringing/odd waveform, but if that is really 1us/div the frequiency is indeed 350KHz, which would point to needing to tweak the timing components around the tl494 a bit to get it down to the same frequiency as your resonator.

indiana

Mon May 11 2009, 05:50AM

Registered Member #2009 Joined: Tue Mar 03 2009, 07:07PM
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Posts: 43

man, i am getting some weird readings off this thing.

still the same setting for the test points, pre gdt, getting 35oKHz. Probe is grounded to the mains ground.

When I test each point separately, the first three gates all test around 425 by the freq counter... which seems to bounce around a lot. from 411 to 450.

Then I test the fourth gate, find it centers about 488, between 450 and 510

Is this frequency counter just effed or what? first time I've used this new scope.

Thing is it reads the test points clear as you like. I think the ringing is just confusing it. It's making me feel crazy. ;P

The waveforms all look the same, and when i change the test point measurement to 250K, the readings on the gate, taken off the actual waveform and not the freak-uency counter, also look appropriate, with a frequency of 250K. (4us period)

I think the ringing is just freaking it out. the counter is all over the map, but the waveforms look consistent all the way through.

I think I'm just gonna have to try it. Or I'm gonna lose my sheet. And I need it for a comfortable night sleep. You know?

hvguy

Sat May 30 2009, 09:27AM

Registered Member #289 Joined: Mon Mar 06 2006, 10:45AM
Location: Conroe, TX
Posts: 154

The period never lies. If it switches one cycle in 4uS than it's 250KHz. The scope counter is just reading wrong, which they often do.

Ah, did yo say MAINS ground?! When reading waveforms off the logic test points the probe MUST be on the logic ground. When reading off the gate the ground MUST be connected to the source of the FET being measured. Any other ground point will give you the wrong reading. Of course, do not take the measurements with the system under power as any connection to the mains would be shorted out through your scope ground.

Keep probing before you run power into this thing. Either your readings or you system have a problem, it would be nice to know which on it is before powering things up

(or, since this reply is about two weeks, late you already know what happens)

indiana

Mon Jun 08 2009, 05:18PM

Registered Member #2009 Joined: Tue Mar 03 2009, 07:07PM
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Posts: 43

i'm going to post this on this thread, should anyone else want to play with the idea, though this question is mostly for dr. gigavolt.

i have a coil i'd really like to try, but it's below the frequency that the board will do right now.

it's resonant at about 56k. i've already added a new external 1k pot in jmp 22, as suggested for fine tuning.

can you think of a quick way to bring the frequency into the 50k range?

HV Enthusiast

Mon Jun 08 2009, 06:56PM

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

indiana wrote ...

i'm going to post this on this thread, should anyone else want to play with the idea, though this question is mostly for dr. gigavolt.

i have a coil i'd really like to try, but it's below the frequency that the board will do right now.

it's resonant at about 56k. i've already added a new external 1k pot in jmp 22, as suggested for fine tuning.

can you think of a quick way to bring the frequency into the 50k range?

Just download the datasheet for the TL494. Its just an RC which sets the oscillator frequency. Using a large C will decrease the frequency. Use the datasheet to determine what values are optimum. There is a formula and graph in there.

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