[massive, massive snip]
Interesting addition to the data.
I agree the OP's data looks horrible. I'm saying that's either
his particular "quasi-defective" MOSFET, or a measurement error
of some kind. Even the poor 1000V mosfets I mentioned weren't
that bad!
I haven't seen a decent description yet of how the OP
configured an N-channel MOSFET into a pullup cc source.
His results had the sniff of a quasi-source-follower.
I have improvised myself a curve tracer and plotted a few devices....
Over a reasonable voltage swing (about 150v) and at 10mA nominal
(minimum) current, I got the following results for drain impedance (dv/
di).
IRF730 (ST!!) 12k
IRF620 (IR) 70k
2SK2350 (TOSH) 200k
yes it is an ST IRF730.... Unfortunately my mosfet draw is a bit
lacking in choice at the moment. Looks like I need to order in a few
samples, and test some more. I guess as Winfield says, maybe the
quality has got worse...
Incidentally, when you say "low-leakage performance for many power
MOSFET types", is that the leakage of the body diode?
Anyway, I see some light at the end of my tunnel, now off to see if I
can track down some Toshiba 400v devices!!
"I agree the OP's data looks horrible. I'm saying that's either his
particular "quasi-defective" MOSFET, or a measurement error of some
kind. Even the poor 1000V mosfets I mentioned weren't that bad!"
I checked another one of the same device, just to check if the first
sample was dodgy, and it was largely the same.
Vgs 0 10 20 50 100
2.6 0 0.0034 0.0037 0.0042 0.0053
2.7 0 0.0078 0.0086 0.0101 0.0129
2.8 0 0.0194 0.0219 0.026 0.0337
2.9 0 0.0506 0.0565 0.0691 0.0909
3 0 0.1343 0.1511 0.1862 0.248
3.1 0 0.3584 0.4139 0.5035 0.6791
3.2 0 0.9528 1.085 1.44 1.99
3.3 0 2.58 3 3.7 5.14
3.4 0 6.49 7.59 9.71 14.16
3.5 0 15.86 18.49 25.06 43
3.6 0 36.05 44.3 65
Hi Tony,
With regards to my original circuit it does look very much like the
below circuit in essence, with a 4M resistor to a variable voltage
source driving the gate. My "load" is connected to the bottom of the
resistor.
o
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o
However, all other measurements since then have been performed on a
bare mosfet by itself, either with lab PSUs and amp meter etc, or the
newly improvised curve tracer, which is a function generator driving
an amplifier and a step up transformer, then bridge rectifier, and A
100R source resistor for current measuring, and a floating psu to
connected directly between the gate and source for biasing. Hope this
is satisfying enough!!
Cheers
Daceo