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Old 1st June 2012, 04:32 PM   #181
NicMac is offline NicMac  Italy
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Locky_Z,
Can the device do transconductance curve tracing like the one showed in post #14 here?
Cheers,
Nic
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Old 2nd June 2012, 03:10 AM   #182
locky_z is offline locky_z  China
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This Vgs-Id curve,
You can load 'N-JFET Vgs-Id' measure condition.

And you can modify the 'Curve type' to control them show in different quadrant.

Example X Axis define is 'Vgs=abs(Vbe)' , abs() mean absolute value,so X-value is all positive,
Y axis define is ‘Id=abs(Ic)’, It is the same positive value.
So the curve will show in the first quadrant.


If you not use abs() function, The N-JFET Vgs-Id curve will show in the second quadrant,The P-JFET will show in the fourth quadrant, then you hard to compare them.
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Old 5th June 2012, 02:12 PM   #183
NicMac is offline NicMac  Italy
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Default troubles and suggestions

After modifying the device to do high current measurements I now obtain very reproducible traces to above 4A with NMOS DUT's. Moving to (complementary) PMOS devices, the curves however go "crazy" (fluctuate) at currents above about 2.5A using equivalent settings.
What is causing this? Anybody else seeing the same thing?

The device auto-numbering feature is useful, but would be much better if it gave an output like: "text-001, text-002, text-003 etc.", rather than: "text-1, text-2, text-3". It is painful to sort the current labeling in software like excel......
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Old 5th June 2012, 03:35 PM   #184
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Quote:
Originally Posted by NicMac View Post
Anybody else seeing the same thing?
You mean like this ?

Click the image to open in full size.

Yes I do.
Curves are for an IRFP9240
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Old 5th June 2012, 03:48 PM   #185
NicMac is offline NicMac  Italy
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Yes, but much less dramatic. My traces continue to rice a still looks a tiny bit like curves.....
I will post an image when I find out how to make window screen shots on a PC and where the shots gets filed (unfortunately I'm a devoted Mac user)....

Edit: is it also P-Channel specific in your case or do you also see it on N-Channel devices?

Last edited by NicMac; 5th June 2012 at 03:52 PM.
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Old 5th June 2012, 04:09 PM   #186
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Also with NMOS, but much more reproductible. The last erratic point is always the same. I can see the overcurrent LED light up so I'm assuming this is linked to the current limiting circuit.

Below is the result for a SemiSouth power JFET (R100). All erratic points line up perfectly (there are several measurements there):

Click the image to open in full size.

Below is an IRFP240:

Click the image to open in full size.
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Old 5th June 2012, 04:37 PM   #187
NicMac is offline NicMac  Italy
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I see those you have shown in the post above when the current "roof" is reached and they are definitely caused by current limiting circuit. Possibly because another measurement is taken after the current has been turned of.

What I observe happens about 1.5A below the current limit.....
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Old 5th June 2012, 08:52 PM   #188
NicMac is offline NicMac  Italy
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Complementary N and P-Channel mosfets.......
Attached Images
File Type: jpg trace.jpg (147.8 KB, 255 views)
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Old 5th June 2012, 08:55 PM   #189
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Quote:
Originally Posted by NicMac View Post
Complementary N and P-Channel mosfets.......
looks like my etch a sketch graph
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Old 5th June 2012, 11:58 PM   #190
locky_z is offline locky_z  China
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Click the image to open in full size.
I think the E-Channel power amplifier become not stable at large current.

The curve tracer‘s measurement is based on the ’VE‘ can not be changed.
VE output by the E-channel power amplifier guaranteed. Instability may have two kinds of situation,one is the output oscillation, one is the output voltage drop increases.


From the gray curve, You can see each point interval narrowing when current more than 2.4A.
This may be E-channel power amplifier output voltage drop increases.
You can view the measure data in the form of the curve, Observed 'Ve' column.
When the current increases, 'VE' value will increase.
Because Vgs=Vb-Ve, Vb increase->Id increase->Ve increase->Vgs reduce,so you see the interval narrowing.
'The power amplifier output voltage drop' control by the paramater 'options->Config‘->Voltage Drop(sink) & Voltage Drop(Source).
When measure N-type DUT, the E-Channel power amplifier is sink current,so the 'sink' parameter control this.
When measure P-type DUT,The E-Channel power amplifier is source current,so the 'source' parameter control this.



But the Green curve like 'sketch',I think it may be oscillation. you also observed 'Ve' column in the form data that the current more than 2.3A.
If the VE is a monotonically increasing or descending, then it is the ‘voltage drop’.
If the VE is random changes, then it is the oscillation.


If it is oscillation, may need replace the LM358 or TIP132/TIP137.
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