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Idea: harmonically driven TC

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Crunchy Frog

Tue Aug 24 2010, 04:11AM

Registered Member #2422 Joined: Tue Oct 06 2009, 02:41AM
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Posts: 85

So I had a thought. What if one were to drive a TC with the primary resonating at half (or maybe less) the secondary's Fres? I ran across this accidentally in a simulation, and it seems to work in the simulator, so why not in real life?

This would seem to help with (for example) headaches getting IGBTs to switch at high frequencies.

I don't have a setup to test this on, but maybe someone else here does.

radiotech

Tue Aug 24 2010, 04:49AM

Registered Member #2463 Joined: Wed Nov 11 2009, 03:49AM
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TV flybacks have been doing this for years ,driven at 15734 Hz and resonating at the 3rd harmonic and later the 5th harmonic.
The makers are very particular in the winding design and there is considerable difference between solid state TV's and the tube ones.

teravolt

Tue Aug 24 2010, 04:51AM

Registered Member #195 Joined: Fri Feb 17 2006, 08:27PM
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Posts: 1111

you could do this but the pulse width would have to be equal to 1/2 cycle so your tesla f=200khz then your pulse width is 5us. A igbt can do about 100khzs max so your wave form would be 100khz or a multipul of 200khz with a 5us pulse width. does this make sense

radiotech

Tue Aug 24 2010, 06:23AM

Registered Member #2463 Joined: Wed Nov 11 2009, 03:49AM
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Crunchy Frog wrote "I ran across this accidentally in a simulation, and it seems to work in the simulator,"

Did your simulation allow changing the coefficient of coupling?
That image in reply to Dingo 27's thread gives some math on the effect of coupling governing which 2 frequencies will be present in both the primary and secondary of a drtc. Also EastVoltResearch mentioned the effect of the arc's capacity changing fres.

"I don't have a setup to test this on, but maybe someone else here does. "

Of course a spectrum analyser would be nice but a simple investigation can be done with the most simple tool-a wavemeter which consists of a variable condenser, from an AM radio and an inductance to resonate around 200-400 kHz , perhaps 300 uHy. A dmm connected to a diode tap on the coil will indicate resonance and the dial of the variable cap can be marked off in frequency.

Dr. Dark Current

Tue Aug 24 2010, 08:47AM

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

I think it would only work at f0/3, f0/5 etc. because a square wave has odd harmonics. This would probably work better for a DRsstc, because in a SSTC the primary current would ramp up to a huge value because of the primary's low inductance.

Hazmatt_(The Underdog)

Wed Aug 25 2010, 02:15AM

Registered Member #135 Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735

Actually, the odd part is the secondary will ring up when the primary is at 2/3 Fo. I was doing some sweeps with my power amps and noticed this, but I can't account for it just yet in simulation, and I need to rebuild my poweramp. I may post more on that later, I dunno, it's hard to do this stuff and work full time.

radiotech

Wed Aug 25 2010, 03:05AM

Registered Member #2463 Joined: Wed Nov 11 2009, 03:49AM
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Hazmatt the Underdog wrote: Actually, the odd part is the secondary will ring up when the primary is at 2/3 Fo.

Yes but that usually sparks up (sic) a furious debate about whether or not subharmonics do in fact exist.

Coronafix

Sun Aug 29 2010, 12:03AM

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

It's called a Perfect Fifth in music! i don't see what the debate could possibly be about.

dex

Sun Aug 29 2010, 05:36PM

Registered Member #2566 Joined: Wed Dec 23 2009, 05:52PM
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radiotech wrote ...

Hazmatt the Underdog wrote: Actually, the odd part is the secondary will ring up when the primary is at 2/3 Fo.

Yes but that usually sparks up (sic) a furious debate about whether or not subharmonics do in fact exist.

I've heard only of higher harmonics (from Fourier analysis).Would you be kind to define and specify meaning of "subharmonics"? I've done some PSPICE simul for DRSSTC excited by 2/3 Fo of secondary natural frequency, with typical coupling of 0.15.All I can see from it is that the power transfer is poor in comparison with Fo excitation...

radiotech

Sun Aug 29 2010, 07:21PM

Registered Member #2463 Joined: Wed Nov 11 2009, 03:49AM
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The debate centers around the fundamental. If a harmonic is a higher multiple of the fundamental then subharmonics are just an as yet not undiscovered fundamental. In Helmholtz, (Sensations of Tone), he states the G S Ohm was the first to declare that there is no form of vibration that will give rise to no harmonic upper partial tones,and therefore will consist soley of the prime tone.

The electrical cases are found in apparent subharmonics in non-linearalities especially in AC ferrite magnetizations. Hence Hazmatt's comment, which is valid in that they do appear. Squedging is common is a lot of stuff, especially oscilators. But he was driving the flyback with something that made it produce multiple signals. his conclusion 3/5 Fo was based on the fact that this was 3/5 of what is ' should' have ringing at. The key word in his send was the word coupling because that is the variable known since spark transmitters
of adjustable to regulate multiple modes.

Back to Hemholtz. .. this a form of vibration pecular to pendulums and tuning forks.. we will call these pendular vibrations, or since they cannot be be analysed into a compound of different tones, simple vibrations.
Helmholtz used an early oscilloscope A smoked drum onto which a stylus made a mark as it rotated.

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