How much current flows through a MOSFET when off?

Other Hardware General Electronics
21

I have often wondered if the o/p 328 rating could actually be a multiple times larger than 40ma

  1. the max guaranteed current is 20mA for 328p, 40mA means the chip may get destroyed
  2. the size of 1n4007 chip is many thousands times bigger than the size of the 328p output transistors - so the 1n4007 can survive much bigger currents in short pulses..
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  1. the max guaranteed current is 20mA for 328p, 40mA means the chip may get destroyed

Yes of course!

23

I'm looking at a IRLZ34N since that is what I pulled out of my "bowl" of spare chips for testing.

Would this be the capacitance in question?

Ciss Input Capacitance 880 pF

And is this the documented static off current?

Idss Drain-to-Source Leakage Current 25 uA (at Vds = 55V)

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Yes.

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International Rectifier recommends using the gate charge spec instead of capacitance to design drive circuitry:

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Idss Drain-to-Source Leakage Current 25 uA (at Vds = 55V)

With 12V the Idss will be much lower, I think.

27

oric_dan:
If you check, you'll also see the leakage for higher-power MOSFETs is much
higher, 25 uA at room temp for IRL540, for instance.

Testing on the bench of my IRLZ34N does not bear out these predictions (nor the datasheet).

With Gate connected to Source (and then to Ground) so that the MOSFET is off, I cannot measure any current flowing from Drain to Source. Certainly less than 100 nA which I think is about the limit of my equipment. This is at 5V on Drain. Even at 24V I can't spot anything.

28

Your transistor - slow without a driver, though..

IRLZ.jpg
IRLZ.jpg730×587 36.3 KB

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Much better with 10ohm in gate (too big inrush current! +/-250mA peaks):

IRLZ1.jpg
IRLZ1.jpg941×610 34.8 KB

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[quote author=Nick Gammon link=topic=174132.msg1294115#msg1294115 date=1372283082]

oric_dan:
If you check, you'll also see the leakage for higher-power MOSFETs is much
higher, 25 uA at room temp for IRL540, for instance.

Testing on the bench of my IRLZ34N does not bear out these predictions (nor the datasheet).

With Gate connected to Source (and then to Ground) so that the MOSFET is off, I cannot measure any current flowing from Drain to Source. Certainly less than 100 nA which I think is about the limit of my equipment. This is at 5V on Drain. Even at 24V I can't spot anything.[/quote]
I just read what the d/s/ said, which is actually the same value as quoted in your d/s.
It's stated as a max value, so they're not making any guarantees in regards negligible
leakage.

31

Maybe yours is a brand new MOSFET that needs a bit of burning in. :slight_smile:

The number in the datasheet is the maximum value. Usually it will be less than that. It's also highly dependent on temperature, the datasheet will give values at different temperatures.