N-channel mosfet

Other Hardware General Electronics
1

Ive got the irf510, a logic level n-channel mosfet. The gate is connected to 3.3V with a 340ohm resistor in between, the drain to the cathode of an led (which is connected to 3V with a resistor in between) , and the source to ground. There is a 3.9K ohm resistor between gate and source.

When I connect base 5V the light is much brighter than when I connected to 3.3V. Why? In the datasheet it says that the Vgs(th) is 2-4V.

And i know there should be a resistor in between gate and 3.3V, but what should its value be?

2

http://www.irf.com/product-info/datasheets/data/irf510.pdf

That is not a logic level mosfet. Its barely turning on at 3.3v and can only conduct a few milliamps at best.

3

Look at Rds(on), not Vgs(th):

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.

4

For 3.3V, you can use e.g. an IRF3708. They seem to be one of the best hobbyist general purpose devices that are cheaply China-available. IRLZ44N also work, but are inferior in most regards.

5

Yep. The irL (note the L) irL is the logic level one. Not the IRF.

eg. IRL540

6

Mostly, but the suggested IRF3708 is logic level.