RE: drsstc

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

Original poster: "Rajesh Seenivasan" <rajeshkvs-at-hotmail-dot-com> 

Dear Mr.Steve,

I am trying to design tesla coil and induction heater at home.
I am trying to use that in my design. I have a doubt in my design. I 
designed a CW
H-Bridge inverter using IGBT bricks. Now, I want to connect a inductance
(tesla or induction heating transformer) and a capacitance (capacitor bank) 
across
the output of two legs of H Bridge inverter. L and C are in series.
So, the resonant freq is given by,
f = 1/( 2*pi*sqrt(LC) )

Now, my doubt is:
Can I run this setup at exactly resonant frequency ? I ask this question 
because i studied that
at resonant frequency, the series LC circuit's impedence becomes ZERO. So, 
if L and C are
connected across the outputs of two legs of HBridge, will it short both the 
output together
because of Zero impedence ?
In other words, how do I calculate the current through the series LC 
circuit at resonant frequency ?

Another doubt:
In one of the message, Mr.Vladimiro said:
"The family (Semikron) 5 is suited to work in square wave >20kHz and in 
resonant mode >100kHz".
Lets consider the resonant frequency is 60kHz. Can I run the setup at a 
frequency more that
resonant frequency, say 75kHz to make sure that current drawn is not huge 
(say, 30A) ?
Will the IGBT be damaged in this case ?

Please clarify my doubt. Thanks in advance.

-Rajesh.




>From: "Tesla list" <tesla-at-pupman-dot-com>
>To: tesla-at-pupman-dot-com
>Subject: RE: drsstc
>Date: Mon, 18 Oct 2004 08:00:42 -0600
>
>Original poster: "Steve Conner" <steve.conner-at-optosci-dot-com>
>
> >I work daily with these brick and I noted that the type used or in plan to
> >use is not the better solution.
>
>I know this. But builders of big coils tend to choose their IGBTs based on
>what they can get cheap on the surplus market. They are just too expensive
>to buy brand new. So we make do with the older, slower bricks, and design
>the coils to have the lowest resonant frequency possible. Steve Ward's ISSTC
>II ran at 40kHz (iirc?) for example.
>
>It helps that we are running in pulsed mode with a low duty cycle, as the
>devices can tolerate much higher switching losses than they could in
>continuous running.
>
>For smaller coils, where the cost of new silicon isn't prohibitive, and it's
>hard to get a low resonant frequency, we use the latest fastest IGBTs like
>the Fairchild SMPS I/II series.
>
>
> >In this moment in europe Semikron company has developed a new generation of
> >short tail IGBT.
>
>I've been looking out for the Semikron '5' devices but they probably won't
>be turning up on eBay for another few years yet :( I picked up some of the
>'3' series ones a couple of months ago. They seem fairly fast, about equal
>to Powerex 'H' series.
>
>Steve C.
>

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