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Goodchild

Fri Sept 02 2011, 06:07AM

Registered Member #2292 Joined: Fri Aug 14 2009, 05:33PM
Location: The Wild West AKA Arizona
Posts: 795

What size wire are you going to use for the 4.5 x 9? I also use a 4.5 x 9 as well and it's wound with 30 AWG wire. Now the thing is that because my coupling is high ~0.4k my upper pole for this secondary is at about 380KHz. If the coupling was lower then this secondary would probably be kinda useless because the upper pole would drop down below 350KHz and as I said that is not good for strait sparks.

I'm hoping that my current ripple will be ok for my already built secondary. If it comes down to having to resort to lower coupling I will end up making a new secondary with a higher F0.

Thanks for offering to share your data, I'm at about the same point you are right now as far as production. I also took a slightly different path as far as control. I didn't want a uC so instead I used dedicated logic. We will have to compare data from our two systems when we finished them both.

Are you going to use a half or full bridge for you design?

BSVi

Fri Sept 02 2011, 06:34AM

Registered Member #1637 Joined: Sat Aug 16 2008, 04:47AM
Location: Kiev, Ukraine
Posts: 83

What size wire are you going to use for the 4.5 x 9?

Oddly, but I was going for 30AWG too (or 0.26mm diameter, since we have everyting metric in ukraine)

Are you going to use a half or full bridge for you design?

I'm going to use half-bridge to half the amount of fried transistors. Power transistors are quite expensive here. Eventually, if I'll have everyting working, and like the result I'll upgrade to full bridge. Whar are you going to use?

Tell me about your primary resonator - what are your L and C values and what's the reason why you chosen that values?

Goodchild

Fri Sept 02 2011, 06:52PM

Registered Member #2292 Joined: Fri Aug 14 2009, 05:33PM
Location: The Wild West AKA Arizona
Posts: 795

I plan to use a full bridge as I have the parts on hand. My primary capacitor with be 15nF making my primary about 11.69uH for 380KHz operation. I wanted a high impedance tank but I also had to work with the parts I had. I happen to have a supper awesome 15nF MICA (thanks to DR Spark) and it is just the right capacitance for my design so it's what I plan to use.

A lot of my part decisions are based on what I have on hand.

Half bridge also makes the control logic a lot easy! With a full bridge you have to have some complex logic in order for your system to keep oscillating while you are skipping cycles. A half bridge will do this naturally because one side of the bridge will pass AC. Although I'm would like to use dedicated logic it's getting to the point were it's just to complex and it would be worth while to use a uC.

May I ask what uC you are using and what clock you plan to run it at? I figured that the clock needs to be at least 4x as fast as the resonant frequency.

Here is the bridge that I'm constructing for my coil
6105452240 0181962700

BSVi

Fri Sept 02 2011, 07:38PM

Registered Member #1637 Joined: Sat Aug 16 2008, 04:47AM
Location: Kiev, Ukraine
Posts: 83

My primary capacitor with be 15nF

That's three times larger than what I'm going for. My capacitance is limited by IGBTs current, so no wonder you have larger cap.

for 380KHz operation

I'm not really shure those bricks you using could be pushed to such a high frequency.

May I ask what uC you are using and what clock you plan to run it at?

I'm using stm32f100c6 for ramp generation (it has DAC), and epm3032 for managing high frequency stuff. The CPLD runs asynchronously so there is no "clock" frequency.

Here is the bridge that I'm constructing for my coil

Omg! My irg4pc40w half-bridge look really feeble compared to this monster!

Goodchild

Fri Sept 02 2011, 11:04PM

Registered Member #2292 Joined: Fri Aug 14 2009, 05:33PM
Location: The Wild West AKA Arizona
Posts: 795

Hehe every one thinks I can't run those IGBTs at 380KHz not even sure I believe it yet, but I have a special trick that allows me to run them that high; all though this will be the first time I test it. I started with 60N60s and they ran ok at 380KHz but it will be a feat if I manage to these suckers running at that frequency.

This bridge should be able to process at least 300A+ of current at QCW duty.

ahhh your using like an FPGA well not the same but similar. Man those things are annoying to program but awesome!

Goodchild

Mon Sept 26 2011, 11:39PM

Registered Member #2292 Joined: Fri Aug 14 2009, 05:33PM
Location: The Wild West AKA Arizona
Posts: 795

Sorry to double post but I have some new information to add.

Ive been doing a great deal of simulation with this type of modulation and I tried two variants. I tried just the comparator (like your design BSVi) and also I tried a delta sigma modulation stage.

Now the regular comparator was dismal in performance. I had very high current ripple throughout the burst and was almost completely unusable. It had a very large 5KHz ripple.

The delta sigma modulator did better, but despite it's awesome name it too has horrible current ripple at least at the beginning of the burst where current needs to be low.

Here is the delta sigma modulator.
6187175372 465688232d B

The primary current is in red and you can see it has some nasty ripple, the ripple increases in frequency and decreases in amplitudes as the burst prolongs as would be expected from a modulator of this type. The regular comparator modulator had the same ripple throughout the duration of the burst.

I tried these simulation with a variety of couplings and tank impedance and the results turn out more or less the same.

Just some fruit for thought! I hope your hardware version is coming along as well? I'm curios to see if this changes with a real system. Although I have a hard time believing it will work in real life if it doesn't work that well in simulation.

Eric

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