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I downloaded the datasheet for this MOSFET, but can't find where it labels the pinout anywhere. Has anyone used these before? I got them for cheap from Amazon, and I'm hoping to control some DC lights with them from an Arduino.

Here's the datasheet: IRL7833

From what I know, these are actually quite old, dating back to the mid 1990's. But I'm thinking that they should work fine. One thing that also confuses me is the max. gate threshold voltage, which is 2.3V. I'm a newbie to electronics, but is that saying the maximum voltage I can output to the gate is 2.3V?

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  • \$\begingroup\$ IRF datasheets are never obvious. Page 9 - the drawing. Match the pin numbers up with the list on the right. \$\endgroup\$ – Majenko Dec 21 '14 at 21:28
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International Rectifier datasheets are never obvious with their pin labels. They hide them in the engineering drawings of the packages.

For instance, the TO-220 package, on page 9 of the datasheet, has this drawing:

enter image description here

The pins are numbered 1-3 and the tab numbered 4. To the right of that drawing is a little table:

LEAD ASSIGNMENTS

  1. GATE
  2. DRAIN
  3. SOURCE
  4. DRAIN

The other packages are even less clear with the table being in tiny text hidden somewhere in the drawing.

The "max" threshold isn't the upper limit for the gate voltage - it's the upper limit of the threshold voltage - the voltage above which you should be to turn it on. The threshold itself could be anywhere between MIN and MAX. As long as you are above MAX then you are good.

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  • \$\begingroup\$ Thanks a bunch, I saw the table of numbers and their respective pins, but was looking through all the drawings to try to find them. I'm a bit confused about the threshold voltage still. So is it saying that the max voltage I can supply to the gate is max when the voltage is 2.3V above the gate-to-source voltage? And why is there a min. threshold V? \$\endgroup\$ – user3211857 Dec 21 '14 at 21:48
  • \$\begingroup\$ No. The threshold voltage is where the switching occurs. Crudely, if the gate voltage is below the threshold, then the MOSFET is off. If the gate voltage is above the threshold then the MOSFET is on. The min->max range is where that threshold lies - between those values. \$\endgroup\$ – Majenko Dec 21 '14 at 21:51
  • \$\begingroup\$ So I must supply the gate with a voltage between 1.4V and 2.3V for the MOSFET to turn on? What if I go over 2.3V? \$\endgroup\$ – user3211857 Dec 21 '14 at 22:39
  • \$\begingroup\$ Nonono. You must supply MORE than the MAX value. It's a THRESHOLD not a LIMIT. "Threshold: the magnitude or intensity that must be exceeded for a certain reaction, phenomenon, result, or condition to occur or be manifested." \$\endgroup\$ – Majenko Dec 21 '14 at 23:03
  • \$\begingroup\$ Ok I got that part. So I just used my Arduino to supply 5V to the gate. And the circuit works. Sorry, but I'm still failing to understand why there is a minimum threshold voltage. If you're supposed to supply more than the maximum threshold value, which is 2.3V, aren't you already above the 1.4V minimum value? What does the minimum mean? Thanks for your help. \$\endgroup\$ – user3211857 Dec 21 '14 at 23:42
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The pin assignments are right with the package information:

http://www.irf.com/product-info/datasheets/data/irl7833.pdf

The maximum voltage you can drive the gate with (with respect to the source) is +/-20V (absolute max, so you shouldn't even get close), and this part needs 4.5V to be guaranteed to turn on well, and 10V is even better.

The threshold gives you some rough idea of where the MOSFET might sort-of start to turn on. Somewhere between 1.4 and 2.3V you'll get 1/4 mA drain current (gate connected to drain for this test). If you want it to turn on properly (Rds(on) < 4.5m\$\Omega\$ ) you need to give it 4.5V or more. It's not really a number of much use for basic design- remember if you only give it 2.3V it may only be able to switch 250\$\mu\$A, and this is a MOSFET capable of 600A pulsed! (in theory anyway).

This is actually quite a nice MOSFET.

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