Re: Terry's DRSSTC - The Bridge...

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: Sparktron01@xxxxxxxxxxx 

Hi Terry

Original poster: Terry Fritz <teslalist@xxxxxxxxxxxxxxxxxxxxxxx>
>
> Hi All,
>
> Parts are coming in for the input power section of my DRSSTC thing :-)
SNIPPO
-----------------------------
>
> A massive ceramic cap to supply the TLP250 with 10 times it's specified
> instant current ;-))  These are relatively cheap parts, so the heck with
> it...  Then the fabulous TLP250 IGBT driver...  Dave turned me on to
> it.  Seems to run IGBTs well over their ratings real good :-)  Since it is
> grounded to zero volts on the low side, a gate discharge diode probably
> just hurts things here...  The TLP250 Is a 2500 Volt gallium arsinide high
> speed opto isolated thing with like 1pF of transfer capacitance...  It is
> powered by a simple "LED"...  Perfect for gate drive signal goofiness to
> follow later...  But be sure to switch those simple LEDs "fast" and no
> cross conduction ;-))

Some other things I learned about these devices I would like to share with 
you and list...

1.  If you use a "speed up" RC network in parallel with normal 10mA 
dropping resistor on  LED  side of otpocoupler will _significantly_ speed 
up operation.  I am getting turn on times of 150ns and turn off times of 
350ns with IRL3803 (110A 30V FET's) with a FPGA controlled high speed load 
bank at work so you CAN drive these guys fast (at least to 100kHz).   R 
should be sized for ~10X normal LED current (i.e. 100mA), C 
of  4.7nF.  With 12V in I was using values of
~91 ohms, with 4.7nF results in a TC of ~470nS, but rise time on LED current is
"fairly fast" [ like <20ns to 10mA, <50nS to Ipeak of 80mA].

2.  Make sure they (the LED signal side) is either ON or OFF.  If you let 
the LED float, the high gan amplifier on the IGBT/FET drive side will 
oscilllate, the output drive amplifier will go into thermal run-away and 
WILL fail.  Guess how I know about this...   :^?  And this occurred with 
proper bypassing and input voltage of +/-12VDC.

3.  A totem pole drive (like a GDT driver driving the OC) will also speed 
up response significantly, especially with turn off since you are hard 
reverse biasing the OC LED, which generally has reverse recovery times of 
<<100ns.

-----------------------------------------------

> http://rocky.digikey.com/WebLib/Toshiba/Web%20Data/TLP250.pdf
>
SNIPPO
>
> Cheers,
>
> 	Terry
>
------------------------

Contact me off list if you need more "poop"...  :^D

Best Regards

Dave Sharpe, TCBOR/HEAS
Chesterfield, VA. USA
>


> Original poster: Terry Fritz <teslalist@xxxxxxxxxxxxxxxxxxxxxxx>
>
> Hi All,
>
> Parts are coming in for the input power section of my DRSSTC thing :-)
>
> http://www.hot-streamer.com/TeslaCoils/MyCoils/DRSSTC/PC090025.JPG
>
> Newark charged my card $200 for the "two" Simpson meters so I guess they
> are on their way too ;-))  The Hammond box's quality was a little low these
> days, but some news screws and a 8-32 tap fixed it...  I hope that 3/8 inch
> brass hardware does not go "poof" :o)))
>
> I am tempted to stuff the controller and inverter in there too, but I
> "need" to keep them separate so the box can do all the fun other uses too...
>
> So I woke up at 3:00 AM last night thinking about the "perfect"
> inverter...  Worked on it all day...  Here is my "totally untested
> resulting thought"...
>
> http://www.hot-streamer.com/TeslaCoils/MyCoils/DRSSTC/DRSSTCdriveThought.gif
>
> Here is the idea, left to right...
>
> The big 4.7uF poly caps take much of the 100kHz+ resonating currents
> reducing the load on the electrolytics of the power section.  Dan does have
> this on his schematics, but I just missed it...
>
> The 240V MOVs are added here for when things go all the heck and trying to
> save components in the case of an explosion...  They are redundant in "my"
> case, but they are "cheap" ;-))
>
> Yes, I do "not" have gate drive transformers or any of that...  I am making
> power supplies off the line voltages available to power the IGBT
> drives...  The 20K resistor, 27V Zener, and 10uF cap (I note your all's
> love for Dan's use of these tan caps :o))) form a little power supply to
> drive the IRFBC30A FET and 1000uF cam to bias a "big" power supply for the
> IGBT drive...  Yes, I am going with higher than 15V gate drive for "sure "!
> :-))
>
> http://hot-streamer.com/temp/OLTC08-30-02.gif
>
> I like to drive IGBTs with heavy voltages to be sure they do not "fold" on
> us...
>
> A massive ceramic cap to supply the TLP250 with 10 times it's specified
> instant current ;-))  These are relatively cheap parts, so the heck with
> it...  Then the fabulous TLP250 IGBT driver...  Dave turned me on to
> it.  Seems to run IGBTs well over their ratings real good :-)  Since it is
> grounded to zero volts on the low side, a gate discharge diode probably
> just hurts things here...  The TLP250 Is a 2500 Volt gallium arsinide high
> speed opto isolated thing with like 1pF of transfer capacitance...  It is
> powered by a simple "LED"...  Perfect for gate drive signal goofiness to
> follow later...  But be sure to switch those simple LEDs "fast" and no
> cross conduction ;-))
>
> http://rocky.digikey.com/WebLib/Toshiba/Web%20Data/TLP250.pdf
>
> The usual 30V transorb to protect the gate...
>
> The IRG4PF50WD is a really cheap (like $6) but capable IGBT (with reverse
> diode)!!  If we can "time" things for that "zero current crossing stuff",
> it won't get too hot...  Maybe like a 1.5 kW system perfect for 120VAC
> stuff....
>
> Important thought!!!  If we run our DRSSTC at 120 Hz,  We can take
> advantage of the AC line high peak currents and vastly reduce the size of
> the filter electrolytic caps...  Why do all that "filtering" when we can
> just run resonate with the AC line too...
>
> The input side "variac" could easily all be "solid state" in this case 
too!!!
>
> Cheers,
>
> 	Terry
>
>
>