MOSFET TESTING

J

Jessica Shaw

Guest
Hi,

I am trying to test the following power MOSFET using digital
multimeter.

http://www.fairchildsemi.com/ds/FD%2FFDL100N50F.pdf

I am using the following way to do this

http://in.answers.yahoo.com/question/index?qid=20061126230136AA6Blij

But this MOSFET is showing anything. Its a new part. I tried another
MOSFET (IRF540) and the test worked fine. I think that FDL100N50F has
large input capacitance. Any advice!

jess
 
"Jessica Shaw" <jsscshaw88@gmail.com> wrote in message
news:44b61e6e-401c-4ecd-a4f7-60a3eb2bc1d3@q29g2000vby.googlegroups.com...
Hi,

I am trying to test the following power MOSFET using digital
multimeter.

http://www.fairchildsemi.com/ds/FD%2FFDL100N50F.pdf

I am using the following way to do this

http://in.answers.yahoo.com/question/index?qid=20061126230136AA6Blij

But this MOSFET is showing anything. Its a new part. I tried another
MOSFET (IRF540) and the test worked fine. I think that FDL100N50F has
large input capacitance. Any advice!
Click to expand...
You can do the most basic test with a 6 or 9V battery, a 6k8 resistor & LED.


Put these items in series to make a simple continuity tester - obviously the
battery + & minus termials will point to ends of the series combination,
call those ends + & minus respectively.

1) place the minus on the source lead & + on the drain - the LED might
partially light due to static on the gate.

2) keep the minus lead on source and touch the + lead on the gate to charge
the gate capacitance - the move + back to drain, the LED should light full
bright to show fully conducting channel - if it slowly fades out the gate
isolation is probably damaged.

3) put the + lead on the source and touch the minus lead to the gate to
charge the gate capacitance with a negative voltage - that should switch the
MOSFET completely off, so when you repeat the minus to source/+ to drain
test; any glow in the LED means leaky.

With P-channel MOSFET the above sequence is repeated with the polarity
reversed.
 
Jessica Shaw wrote:
Hi,

I am trying to test the following power MOSFET using digital
multimeter.

http://www.fairchildsemi.com/ds/FD%2FFDL100N50F.pdf

I am using the following way to do this

http://in.answers.yahoo.com/question/index?qid=20061126230136AA6Blij

But this MOSFET is showing anything. Its a new part. I tried another
MOSFET (IRF540) and the test worked fine. I think that FDL100N50F has
large input capacitance. Any advice!

jess
Click to expand...
With todays DMM's that test, in my opinion is bogus. The best you can
maybe expect is to drain the gate down a bit from where it is and there
for it just turns off the mosfet. Unless of course, you have a unit with
a very low Vg(th), but that does not appear to be in your case.

You see the problem is, circuits operate at low voltage and it is not
good to be putting voltages much over 1.5 in the circuit.

The mosget you have there requires 3 volts at the gate. I don't think
your DMM is generating that much, other wise, it could be damaging when
using the DIODE mode for in circuit testing..

At one times they did 2 volts with a diode test. I am not sure what
they do now. BUt you at least have to get a good margin above a diode drop.

What I do when I am not sure about the Vg(th) value, or if the unit
even works properly. Is use a Resistor from a power supply that can
do at least 12 volts for example.. Like below..




Variable voltage

+-----------+------------+
+ + |
/+\ |
( ) 12V |
\-/ +
| .-.
| | | 1k
=== | |
GND '-' V Meter
| _
+ / \ |
o----------------o------------o-(_/_)-===
| | D \_/ GND
| |
| +
| ||-+
| G ||<- Device Under Test (DUT)
o------o------||-+
+
| S
|
|+
===
GND


You should get a full volt reading when the supply is below the Vg(th)
level and up to the Vg(th) and a little more, depending on how high you
have the supply voltage.
 
On 6/12/2012 5:19 PM, Jamie wrote:
Jessica Shaw wrote:
Hi,

I am trying to test the following power MOSFET using digital
multimeter.

http://www.fairchildsemi.com/ds/FD%2FFDL100N50F.pdf

I am using the following way to do this

http://in.answers.yahoo.com/question/index?qid=20061126230136AA6Blij

But this MOSFET is showing anything. Its a new part. I tried another
MOSFET (IRF540) and the test worked fine. I think that FDL100N50F has
large input capacitance. Any advice!

jess

With todays DMM's that test, in my opinion is bogus. The best you can
maybe expect is to drain the gate down a bit from where it is and there
for it just turns off the mosfet. Unless of course, you have a unit with
a very low Vg(th), but that does not appear to be in your case.

You see the problem is, circuits operate at low voltage and it is not
good to be putting voltages much over 1.5 in the circuit.

The mosget you have there requires 3 volts at the gate. I don't think
your DMM is generating that much, other wise, it could be damaging when
using the DIODE mode for in circuit testing..

At one times they did 2 volts with a diode test. I am not sure what they
do now. BUt you at least have to get a good margin above a diode drop.

What I do when I am not sure about the Vg(th) value, or if the unit
even works properly. Is use a Resistor from a power supply that can
do at least 12 volts for example.. Like below..




Variable voltage

+-----------+------------+
+ + |
/+\ |
( ) 12V |
\-/ +
| .-.
| | | 1k
=== | |
GND '-' V Meter
| _
+ / \ |
o----------------o------------o-(_/_)-===
| | D \_/ GND
| |
| +
| ||-+
| G ||<- Device Under Test (DUT)
o------o------||-+
+
| S
|
|+
===
GND


You should get a full volt reading when the supply is below the Vg(th)
level and up to the Vg(th) and a little more, depending on how high you
have the supply voltage.
Click to expand...
Jamie, you recommended what I was going to, set up a circuit for
the Mosfet. But I would have put a *voltage divider on the gate.
10k from 12v to gate and another 10k from gate to ground, then put a
switch from gate to ground. With this she can watch the Mosfet switch
on/off with changes in the position of the switch. Maybe even use a 100
ohm or 10 ohm from 12 v to Drain to get a little current flowing.
Just my two cents.
Mikek

*this assumes removing the gate to 1k/drain connection in your circuit.
 
"Jessica Shaw" wrote in message
news:44b61e6e-401c-4ecd-a4f7-60a3eb2bc1d3@q29g2000vby.googlegroups.com...

Hi,

I am trying to test the following power MOSFET using digital
multimeter.

http://www.fairchildsemi.com/ds/FD%2FFDL100N50F.pdf

I am using the following way to do this

http://in.answers.yahoo.com/question/index?qid=20061126230136AA6Blij

But this MOSFET is showing anything. Its a new part. I tried another
MOSFET (IRF540) and the test worked fine. I think that FDL100N50F has
large input capacitance. Any advice!
Click to expand...
Your link to the data sheet didn't work for me, but this does:
http://www.fairchildsemi.com/ds/FD/FDL100N50F.pdf

I use that trick sometimes, and it is quite useful. I use the diode check
which may put out as much as 3 volts or more (which is useful for LEDs as
well), and then check the D-S resistance. Then short G-S and read open in
one direction and the body diode in the other. It is good to see if the
input gate resistance is high enough to hold the charge while you take the
reading.

As noted, your MOSFET has a gate threshold of 3-5 volts, so you will need
something like a 9V battery to get enough voltage. You COULD charge a
capacitor with the multimeter voltage and then put it in series with the
multimeter to the gate to get 4-6V. Just in case you didn't have a spare
battery but had a capacitor handy.

Paul
 
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