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Old 13th July 2011, 05:05 AM   #11
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These are switching parts. If you want to use them for linear, then you
must adjust to their characteristics. 100 uA of leakage is not an issue
unless you don't know about it...

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Old 13th July 2011, 06:57 AM   #12
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The inconsistency (and indeed, the high leakage to begin with - this is far worse than Si parts with much lower breakdown voltages) will be an issue (does it mask or harbinger other issues? Does the company really have their process under control?) to those who might want to use it in a consistent manner in its intended switching application in mass production, especially as their customers expect low PPM failure rate (and really get worked up even about that) under all sorts of conditions, all for a pittance. I'll be asking some questions back-channel, though that really doesn't have that much to do with matters here.

I'll go ahead and use a low impedance driver circuit of some sort for this project, but I don't really like it all that much - it takes a fair amount of the shine off the part, especially given the high asking price. It'll be interesting to see if similar GaN parts work any better.
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Old 13th July 2011, 04:55 PM   #13
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Default SiC's and Electrostatics

Interesting voltage domains, for the SiC semiconductors.

Any possibility/feasibility of "stacking" SiCs, so that they could directly drive ESL panels (with say, 2-3kv of DC bias on the panels)?

That would really excite me.....!
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Old 13th July 2011, 05:00 PM   #14
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Default or SiC's, as Class D drivers for Electrostatics?

A second thought: possible to use the SiC's in their switching mode, as pulse-width modulated (Class D) drivers for ESLs? Depending on the PWM switching frequency, feasible for the ESL network to filter out?

Just thinking out loud.....

Potentially some interesting opportunities for direct drive electrostatics...... Anyone care to chime in?
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Old 13th July 2011, 06:24 PM   #15
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Start a new thread for that purpose, if you really want to go there.
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Old 13th July 2011, 06:54 PM   #16
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How does it sound ?
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Old 13th July 2011, 09:57 PM   #17
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Quote:
Originally Posted by wrenchone View Post
it takes a fair amount of the shine off the part, especially given the high asking price. It'll be interesting to see if similar GaN parts work any better.
You can always use a Mosfet, where the Gate leakage is virtually zero.
Unfortunately I haven't encountered a Mosfet that sounds as good as these
parts.

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Old 13th July 2011, 10:01 PM   #18
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Still working on thermal and bias stability issues. It looks like the part will need the very best insulator pad in order to dissipate the heat without undue temperature rise. I'm going to order some aluminum oxide pads from Mouser. Even though the part is SiC, I want to keep the die temp at 100C or below. I also don't know anything about the tempco of the gate leakage, though I would assume that it would rise with die temp. At present, I'm getting about 0.15V gate voltage with a 10k gate pulldown, meaning I'm getting about 15uA of gate leakage. The part I have in the board right now needs about 12V of reverse bias for 150mA - I may change it for one with lower reverse bias requirement, as this makes the source resistor rather toasty.
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Old 13th July 2011, 10:26 PM   #19
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To make it clear, I'm continuing with the Semisouth parts on this design, as they have the dissipation capability and voltage rating to run comfortably at vacuum tube voltage levels. The Ixys 500V parts would be a little marginal for the application unless I ran higher drain currents and lower B+, which is not compatible with the transformers I'm using. I have other plans for the Ixys depletion mode parts I have on hand. I just characterized a lot of 10 pieces for Vgs at 1A drain current in order to get some matched pairs. A possible project with these is a Susan Parker "Zeus" amplifier. I may also try something similar to what Nelson has done commercially with the Semisouth parts, but using the Ixys parts instead. These projects will get separate threads when I actually start something.
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Old 14th July 2011, 02:16 AM   #20
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How about a circuit diagram?
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