Output characteristics of IRF540 MOSFET

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Output characteristics of IRF540 MOSFET

Postby arivalagan13 » Mon Mar 18, 2013 9:20 am

Hello all,
Am in the process of deriving the output characteristics of IRF540 MOSFET..
I did the following:
To the gate +5Vdc was connected(chosen so that Vgs> Vth)..
Then to the drain I connected a varying voltage source of 0-30Vdc..
As I varied the Vds from 0 through 30V i noticed zero current through drain..
Why din't i get non-zero drain current? Can somebody help me in deriving the
output characteristics of this MOSFET?

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Arivalagan M
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Re: Output characteristics of IRF540 MOSFET

Postby danadak » Mon Mar 18, 2013 12:52 pm

Source is connected to ground ? Keep in mind Rdson is 44 mOhms, did you trip the
power supply crowbar or fault current and shut its output off ? Some supplies need
to be reset when this happens.

Or did you burn it out ? Per specs at 1 V Vds you would be drawing I = 1/.044 >= 23 Amps
and dissipating 23 W, if it was not heat sunk it was cherry red.

IRF540.jpg
IRF540.jpg (48.25 KiB) Viewed 3894 times


Regards, Dana.
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Re: Output characteristics of IRF540 MOSFET

Postby arivalagan13 » Mon Mar 18, 2013 9:54 pm

Yes, source is connected to ground.
Then,my power supply limits current to be 2A max.(if am missing something p.s give me more explanation)
You said the drain current @ 1Vdc is 23A.the graph you posted also shows the same.but,the graph i have(http://www.datasheetcatalog.org/datashe ... s/9387.pdf)
shows something different.(first graph of page 4 in the above link). As the Rds(on) is very high should i apply high voltage to observe some finite current,Id...

i already applied up to 20V b/w Vgs and up to 30V b/w Vds..

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Re: Output characteristics of IRF540 MOSFET

Postby danadak » Tue Mar 19, 2013 2:06 am

If you apply Vgsth = 10 V, then Rdson <- .077 ohms.

That will essentially short your power supply used for Drain to ground.
So what does the supply due when its output is grounded ? Does
it have foldback current limiting ? See left hand graph. Depending
on supply some will foldback to 0 current.

http://www.google.com/imgres?imgurl=http://de.tdk-lambda.com/content/glossary/128522123940958750_Current%2520Limit%2520Knee%2520image.png&imgrefurl=http://de.tdk-lambda.com/public/kb_glossary_results.aspx?index%3DC&h=212&w=454&sz=7&tbnid=2eneCtEuBXDSvM:&tbnh=61&tbnw=130&prev=/search%3Fq%3Dfoldback%2Bcurrent%2Blimiting%26tbm%3Disch%26tbo%3Du&zoom=1&q=foldback+current+limiting&usg=__nxBLI0jD2G5-5KIjpX019DftLHQ=&docid=4HpXyv_6Tb0E9M&hl=en&sa=X&ei=NDhIUZKQNoTk4AO6_oCgDw&ved=0CD4Q9QEwBA&dur=5306

A simple bench test would be use a load in drain, say 10 Ohms, connected to 5V supply. Apply
10 V Vgs to gate, and measure drop across 10 Ohms. If you do not see any drop across 10 Ohms,
eg, Vds = ~ 5 V, no drop across 10 ohms, MOSFET is toast. Tie MOSFET gate to ground, use ohmmeter,
measure Rds, it should be very Hi Z. With Drain ties to Source, ohmmeter, measure Gate to Drain/Source,
that should be Hi Z also. If neither is true you may have blown gate oxide, maybe static.

Regards, Dana.
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Re: Output characteristics of IRF540 MOSFET

Postby arivalagan13 » Tue Mar 19, 2013 2:43 am

Ok Dana, now i understand your point...
I'll verify experimentally the points that you have mentioned..
Now,is it possible to give me a suggestion(if possible a circuit connection) to observe some drain current?
Regards
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Re: Output characteristics of IRF540 MOSFET

Postby danadak » Tue Mar 19, 2013 3:10 am

A simple bench test would be use a load in drain, say 10 Ohms, connected to 5V supply. Apply
10 V Vgs to gate, and measure drop across 10 Ohms.


Or put an ammeter in series with 10 ohms.

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