Re: 1-turn coil inductance nomogram

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Terry Fritz" <twftesla-at-qwest-dot-net>

Hi Jimmy,

If your going to switch really fast (low or no gate resistitor on the IGBTs)
you may want to try a 20 volt TVS transorbe between the gate and emitter of the
IGBTs.  Marco is much more expert on this than I, but fast switching can cause
voltage spikes on the gate which can fail the part.  A TVS (like DigiKey part
number SA20ADICT-ND) may really help this problem.

Be sure to check out the problems and solutions in Marco's paper at:

http://personal.inet.fi/atk/dncmrc/slrconv.zip

Cheers,

        Terry


At 05:16 PM 8/26/2002 -0700, you wrote: 

>
> the igbts i am going to use for my sstc are IRG4PC40W. they are rated at 600v
> 40 amps continuous 160 amps peak have a fall time of 74ns and a rise time of
> 23ns. the best part is they only cost $3.80 from digikey. the 1450 amps you
> are talking about is only the magnetizing current, the current that doesnt
> help you. current that helps you is the current that is in phase with the
> voltage, and it builds up over time. the way to keep the magnetizing current
> low and the in phase current high is to have a high k. it would be easier to
> use the magnifier setup to get a high k with out insulation problems. if the
> magnetizing inductance is high enough then the transformer acts like a gear
> ratio and it is just like base feeding the resonator, but at a higher
> voltage. 
>
> Tesla list wrote: 
>>
>> Original poster: "K. C. Herrick by way of Terry Fritz " 
>>
>> I don't know if this will be new to the List or not but I'll prevail on
>> Terry to put up http://hot-streamer-dot-com/temp/Loop-L.gif. It returns
>> inductance of a 1-turn loop using the loop- and conductor-diameters. I
>> found it in one of my ancient textbooks.
>>
>> It prompts me to notice that the inductance of a 12"-dia. x 1"-tube
>> 1-turn primary is just about 0.5 uH (and no doubt Terry reported
>> something like that for his OLTC). That yields ~0.44 ohms reactance at
>> 140 KHz and if I were to put 640 V across that, I'd need to switch 1450 A
>> in a reconfigured s.s. primary, thru a bunch of MOSFETs (assuming much
>> less resistance in the circuit). So there's why I've gone to 3 turns at
>> present, suffering the consequences.
>>
>> 1/4" dia. tubing only increases the inductance to! ~0.75 uH, resulting in
>> 967 A. 
>>
>> IRFP460A MOSFETs are rated at 85 A Idm -at- 25 C. IXYS VMO 60-05F's, on the
>> other hand, are rated at 240 A Idm -at- 25 C. The 460As are $2.80 each/25
>> (from Fortune) or 3.3¢ per Idm Amp; and I recall the IXYS being quoted
>> recently at about $40 a pop (unfortunate word but there it is) or 17¢ per
>> Amp.
>>
>> Idm is the maximum for a 10 us pulse width, being limited by the
>> junction-temperature rise during that interval, so it's probably a safe
>> rating to use in choosing the quantity of transistors in this
>> application, perhaps holding the spark duty-cycle to a modest value. 
>>
>> Hmmm...using the 1" tubing, 1450/85 x 2 x 4 = 136, 460As are needed vs.
>> 1450/240 x 2 x 4 = 48, 60-05Fs. 
>>
>> Hmmm...did I hear someone mention IGBTs? Which ones are going to turn on
>> & off nicely in no more than 1 us, I wonder?
>>
>> Ken Herrick
>
>
>
> JImmy
>
>
>
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