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Re: [TCML] triac or scr choice
Dave,
It's already been done: http://www.youtube.com/watch?v=AvMJBcx55Eg&feature=channel Coil uses a CM600 in the cathode circuit and operates very similar to a drsstc. I don't recommend using this configuration in "level shift" or AC mode as you will super-nova the IGBT instantly. Using an IGBT I have found it necessary to use full wave rectified DC (rather well filtered) as IGBT's don't like the AC component. I disagree with the statement : "A 10A device is capable of controlling a 10-20kV VTTC...EASILY" as the actual circuit falls under the classification of "cathode modulation" which by all rights half the plate supply would be across the plate tube and the other half across the modulation device at 50% duty cycle...At 20kv you can expect the drop across the IGBT to be in the neighborhood of about 10kv!...not good for a 1.2kv device. You are correct in that (when properly done) the response time would be significanly faster than an SCR or Triac.
Looking forward to seeing your achievements,
Hank
> [Original Message]
> From: <sparktron01@xxxxxxxxxxx>
> To: Tesla Coil Mailing List <tesla@xxxxxxxxxx>
> Date: 2/26/2009 7:46:12 AM
> Subject: Re: [TCML] triac or scr choice
>
> Folks
>
> An interesting experiment (which we are in early stages of performing) is replace the
> stoogy old SCR with a nice gleaming new IGBT. Why? Well...
>
> 1. You can cut if OFF in microseconds, thereby protecting the VT is anything goes POOF!
> 2. You can turn it on with LESS drive then an SCR, and it will turn on at least 10X faster
> (again easily single digit microseconds).
> 3. An IGBT has arguably as good a di/dt rating as a SCR. If you think not, how about
> those things called eh eh DRSSTC's out there, and their "little peak currents" (1kA + ;^D )
> 4. 1.2kV devices are available from multiple sources, and Ic rating does not have to be
> outrageous. A 10A device is capable of controlling a 10-20kV VTTC...EASILY with
> less then 30W dissipation when on ( at a Vce ON of betwen 2.2-2.5V)
> 5. Staccato control will have to be modified to stay on during postiive alternation, or much
> more interestingly, turn the oscillator off early (150-500 microseconds), just like a
> DRSSTC. I "think" that might reduce the VT dissipation as well, "just a little" ;^D
>
> Regards
> Dave Sharpe, TCBOR/HEAS
> Chesterfield, VA USA
>
>
> ----- Original Message -----
> From: futuret@xxxxxxx
> To: tesla@xxxxxxxxxx
> Sent: Wednesday, February 25, 2009 5:41:44 PM GMT -05:00 US/Canada Eastern
> Subject: Re: [TCML] triac or scr choice
>
> Christoph,
>
> It's better to use an SCR. THey are built in a more robust way than
> a triac.
>
> John
> --
>
>
> -----Original Message-----
> From: Christoph Bohr <cb@xxxxxxxxxxxxxxx>
> To: Tesla Coil Mailing List <tesla@xxxxxxxxxx>
> Sent: Wed, 25 Feb 2009 7:29 am
> Subject: [TCML] triac or scr choice
>
>
>
> Hello everyone..
>
> which type of triac or similar device should one use in
> conjunction with a VTTC staccato controller?
> I have found the shematic at the eastern voltage research
> homepage and was wondering what kind of device I could use
> to swith the cathode of a tube around 1KVA
>
> Any suggestions are appreciated.
>
> regards
>
> Christoph Bohr
>
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