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Old 27th March 2013, 02:11 PM   #31
tony399 is offline tony399  United Kingdom
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Understood
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Old 27th March 2013, 02:20 PM   #32
tony399 is offline tony399  United Kingdom
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Quote:
Originally Posted by dodo View Post
those resistor just have to reduce the current , so the power dispation would be within jfet limit
And both voltage source polarities reversed for P channel J74 I assume.
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Old 27th March 2013, 02:33 PM   #33
dodo is offline dodo  Poland
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Old 27th March 2013, 04:04 PM   #34
tony399 is offline tony399  United Kingdom
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Is this schematic slightly wrong?

I set up for both N and P channels and was not getting any current flow.
When I removed the source voltage for the gate ie gate at source voltage through R2 then the Vds dropped and I got current flow.

Is it the polarity of Eg shown the wrong way round in the diagram (for N channel set up)?

I haven't tested this yet because my dual variable supply is +V 0V -V.

The resistor values I am using are;
R1 - 5k1
R2 - 560k
Rd - 2k
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File Type: jpg Jfet_N_messurements_schem.jpg (30.7 KB, 474 views)
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Old 27th March 2013, 05:02 PM   #35
tony399 is offline tony399  United Kingdom
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Think I have found the problem, my supplies have a minimum output of 1.25V which is enough Vgs to 'switch off' the current flow.
Have slightly modified the circuit and at 10V Ed get around 5mA with 0Vgs, increasing Vgs reduces Ids and zeros around 0.6Vgs.
Hopefully can start taking some meaningful measurements now!
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Old 27th March 2013, 07:14 PM   #36
tony399 is offline tony399  United Kingdom
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First measurements for one J74, I'm not sure exactly what is required so take a look and let me know.
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File Type: pdf J74 measurements.pdf (494.2 KB, 101 views)
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Old 27th March 2013, 08:53 PM   #37
dodo is offline dodo  Poland
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messure at Vd-10V and make the graph Vgs/ Id , compare with graph attached in the data sheet for J74 , it will confirm , your devices are origin Toshibas
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Old 27th March 2013, 09:50 PM   #38
tony399 is offline tony399  United Kingdom
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Quote:
Originally Posted by dodo View Post
messure at Vd-10V and make the graph Vgs/ Id , compare with graph attached in the data sheet for J74 , it will confirm , your devices are origin Toshibas
Have done that and looks good to me, just trying to get in a file/format/size that will be acceptable to upload, I really don't like computers sometimes!
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Old 27th March 2013, 10:00 PM   #39
NicMac is offline NicMac  Italy
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Quote:
Originally Posted by Salas View Post
Get a Peak DCA75 made in the UK.
WOW - what a device
No need for google and data sheets anymore.......
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Old 27th March 2013, 10:09 PM   #40
tony399 is offline tony399  United Kingdom
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J74 graph resize.bmp
Finally!
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