I have just measured using a multimetre the resistance / voltage between drain and source of all of the 4 x DN2540 I have. It shows 10R / 0.006V. It measures open (infinite resistance / 0V) between gate and drain, and between gate and source.
Are these fake parts? or are these N-Channel depletion-mode vertical DMOS FETs supposed to show measurements like this?
All 4 of them are straight from the supplied bag. I have not even touched them with my hands. They would not be damaged by EDS.
I ordered them from Mouser (689-DN2540N5-G $2.84 each). I have never had problems with parts from Mouser.
Are these fake parts? or are these N-Channel depletion-mode vertical DMOS FETs supposed to show measurements like this?
All 4 of them are straight from the supplied bag. I have not even touched them with my hands. They would not be damaged by EDS.
I ordered them from Mouser (689-DN2540N5-G $2.84 each). I have never had problems with parts from Mouser.
It looks like you have the real part.
I have a bunch of the DN2540's from Mouser here in both the N3 (T0-92) and N5 (TO-220). I just measured a few of the N3's and get the same thing you did. On a Fluke 289, around 10.72R, 9.76R, and 10.40R drain to source (meter leads either direction) respectively on three different parts. I get around 11mV, 9.9mV, and 10.3mV on diode test from drain to source (meter leads either direction) on the three parts. Infinite ohms from gate to either drain or source on all three, which is expected since it is still a mosfet. The channel is just doped open to make it depletion vs. enhancement, but there is still a layer of glass insulator (silicon dioxide) between the gate and anything else, same as with an enhancement mosfet.
The data sheet shows a maximum drain-source resistance of 25R, so we are doing well to get around 10R.
http://www.supertex.com/pdf/datasheets/DN2540.pdf
The DN2540's rock as constant current sources.
I compiled test results a year ago with 12 different DN2540's and sent them off to a tech person at Supertex showing that the parts work quite well for a CCS with just 3 or 4 volts across the part, despite the part's high voltage rating. I had read comments in postings that the DN2540s were only useful for higher voltage current sources. That is just not the case.
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agdr,
Thanks a million.
That is fantastic. I am using DN2540 in a cascode for CCS for a CCS plate load of a tube preamp. It is good to know that it works with any voltages as I have two transformers with different output voltages and I can use the same CCS for different B+ without a worry.
Regards,
Bill
Thanks a million.
That is fantastic. I am using DN2540 in a cascode for CCS for a CCS plate load of a tube preamp. It is good to know that it works with any voltages as I have two transformers with different output voltages and I can use the same CCS for different B+ without a worry.
Regards,
Bill
Well drain and source I have 10R to 11R the same, but after use 30 minutes gate and source change from infinite resistence to 11k. I load the 6e5p
is this normal or I burn the dn2540, others causes?
Mosfets have a gate charge.
If you charge up the gate capacitance with a diode tester it will be on until such time as it has discharged again.
They do indeed have "memory" when they are out of circuit.
If you put the positive lead of the diode tester on the gate and measure it while it is switched on you will get a low reading.
If you put the negative lead of the diode tester on the gate and measure it again you will get a high reading because you will have turned it off.
Static from your body will charge the gate and switch it on as will touching it with a damp finger.
Test it again with a 1 meg resistor between G and S and then remove the resistor and dab it with your finger with the diode tester still connected it will pick up static or a strong local radio station and turn on.
Modern FETs have enough static protection built in for this not to harm them.
If you charge up the gate capacitance with a diode tester it will be on until such time as it has discharged again.
They do indeed have "memory" when they are out of circuit.
If you put the positive lead of the diode tester on the gate and measure it while it is switched on you will get a low reading.
If you put the negative lead of the diode tester on the gate and measure it again you will get a high reading because you will have turned it off.
Static from your body will charge the gate and switch it on as will touching it with a damp finger.
Test it again with a 1 meg resistor between G and S and then remove the resistor and dab it with your finger with the diode tester still connected it will pick up static or a strong local radio station and turn on.
Modern FETs have enough static protection built in for this not to harm them.
Just to add to theFAKE news about the DN2540:
I ordered from China (Alithing) and I got a batch that is not a Depletion-Mode FET at all.
I tested and the Vgs must be about + 3 volt before there is conduction in these fakes.
Too bad I did not check them when I received them.
This is a silly scam of course. It is the first you will notice (normally that is, but I was not on my guard).
They look just like the ones I bought from Farnell two years back (that are OK).
I ordered from China (Alithing) and I got a batch that is not a Depletion-Mode FET at all.
I tested and the Vgs must be about + 3 volt before there is conduction in these fakes.
Too bad I did not check them when I received them.
This is a silly scam of course. It is the first you will notice (normally that is, but I was not on my guard).
They look just like the ones I bought from Farnell two years back (that are OK).
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