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Old 9th February 2013, 04:36 PM   #101
flg is offline flg  United States
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Well buzz, where did that come from? Under what other conditions? It's blurry and there is no legend so I'm gussing what most of it is. Are those Vgs trend lines? Are they -4.8V to -6V w.1V intervals ? I've seen this before I think and even played with the load line possibilties. I think I had a problem similar to you. I have other projects to finsh so I put it away for awhile...
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Old 9th February 2013, 04:37 PM   #102
Gyuri is offline Gyuri  Hungary
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Ah, I forget to mention, I was carried out those measurements with an constant 9V voltage source and a 2.7 kOhm resistor.
I got exactly the same results, with all of my four SJEP120R100A.
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Old 9th February 2013, 04:40 PM   #103
flg is offline flg  United States
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Quote:
Originally Posted by Gyuri View Post
My Toellner 7711 function generator has a DC offset function it's perhaps an useful feature in this case, isn't it?
Sure, you bet. I have an older HP and I can do DC(offset) or AC.
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Old 9th February 2013, 04:59 PM   #104
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Well, I put a little thought into it. I'm thinkin I can use the circuit attached below? Comments are welcome:
My Function Generator can produce a single + Pulse, I'm thinkin maybe 1ms long, so as not to get to much device heating. I will be going for the 25C data since anything else is a little difficult to do right now. Typically we do these measurements within 100-200uS. We'll see what the measurements look like? I can also vary the pulse amplitude in relatively small steps.
The 100 ohm should'nt induce much of any error but, save me from oscilating to death. One of those accidents I was thinkin of.
The .05 ohm Drain R is "current shunt" to measure the Ids. It's big enough to measure voltage accurately but, not big enough to eat up my Drain voltage when current is flowing. It's also big enough physically to not induce to much Tc variation from heating.
I will use a storage scope triggered on the Func Gen pulse to capture these 2 voltages. In the past I remember having to use some diodes in the set-up to avoid the scope input saturation due to the range it needs to be on but, I don't think that's an issue here. That's probably the Rdson test I'm thinkin of.
Does anyone see any issues? Have any suggestions?
The parts are pretty rugged drain to source, but at elevated Vds, I'd shoot to make the measurement in much less than 1 ms to avoid self heating. But you're already on top of that.

It's gate reverse bias that is the SemiSouth JFET's Achilles heal. Don't stress the reverse blocking of the gate-source diode unless you're prepared for the consequences.

Your concern that oscillation may produce a bad day is well founded, but your provision for 100 Ohms should be more than enough to kill the nasty oscillations before they multiply, as long as you keep the interconnections relatively tight to avoid too much gate- and drain-loop inductance.

My research team is actively working on the problem of self-oscillation with power switching circuits using SiC transistors. Our lab has dead bodies surrounding the test bed that led to our most recent paper in IEEE Transactions on Power Electronics Letters (IEEE Xplore - Stability Considerations for Silicon Carbide Field Effect Transistors). The paper is so recent it is still available only in the preview volume "99."
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Old 9th February 2013, 05:01 PM   #105
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Ah, I forget to mention, I was carried out those measurements with an constant 9V voltage source and a 2.7 kOhm resistor.
I got exactly the same results, with all of my four SJEP120R100A.
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Old 9th February 2013, 05:45 PM   #106
Gyuri is offline Gyuri  Hungary
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Originally Posted by generg View Post
Oh, one was lost by failure and two went to a friend for an F2J....
I still listen to those two on the left side.
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Old 9th February 2013, 05:55 PM   #107
generg is offline generg  Germany
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ha, ha thank you that you took the heart side for them.....!

and not the dull right side......

and not forgotten, I got two wonderful LT1014 on a copper block from you and the pleasure hearing the F3s voice....
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Old 9th February 2013, 06:08 PM   #108
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and not forgotten, I got two wonderful LT1014 on a copper block from you and the pleasure hearing the F3s voice....
Do you have a picture or drawing of the "cooling" copper block ???
Or was it @Gyuri that was the creator ??
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Old 9th February 2013, 06:12 PM   #109
Gyuri is offline Gyuri  Hungary
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Take a look here:
https://tjeyca.bay.livefilestore.com...001.JPG?psid=1

Wacky
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Old 9th February 2013, 06:16 PM   #110
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Superb

Who need SiC JFETs when the LU1014D can dissipate enough heat with your copper blocks

Last edited by RayCtech; 9th February 2013 at 06:25 PM.
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