I found a thread that discussed exactly what i am trying to sort out, but when i tried to reply i got a message saying the thread was more than 6 years old, try posting a new one.
I am trying to use an N Channel mosfet to turn on a 10W LED, using an RCWL-0516 radar sensor as the trigger. But this sensor outputs a 3.3v signal, and after hours and hours of trying to figure out why i couldn't do something as simple as use a mosfet (IRF610) as a switch, I found the thread in this forum that said this type of mosfet needs 10v to fully turn on. I had found that if i used 5v instead of 3.3v, i got a lot more current, but that was just a jury rig trying to troubleshoot the problem.

One poster in the thread said what was needed (if the gate was less than 10v) was a logic level mosfet. And another poster pointed out that if you read the graph showing gate to source voltage vs. source current in the datasheet you can get a good idea of how the transistor will perform. I did, and I went to ebay and began looking at logic level N Mosfets, and one by one going to the data sheets and reading the graphs.

I have found one which I think will do the job, but (and it is probably pretty obvious) I find 99.5% of the info on the data sheet a complete mystery.
So the point of this post is that I am hoping someone can tell me if this will do the job for me (or suggest a better one). I just don't want to buy one and wait a week or two, then find out that it won't work for me because it has a left handed johnson rod and i needed a right hand, as is clearly indicated in the datasheet.

The source voltage is 12v dc. I need about 40 mA to drive the lights (it doesn't equal 10W, but it's plently bright). I will be using a gate voltage of 3.3v.
I am looking at a IRLB8743PBF.

Anybody ?

 

For sure you can use IRLB8743PBF or IRLZ44 or any "Logic-Level" MOSFET you can find.

But if your's LED's current is only equal to 40mA. In this case, you do not need a MOSFET.

You can use any small-signal BJT with the base resistor around 470Ω

 

For sure you can use IRLB8743PBF or IRLZ44 or any "Logic-Level" MOSFET you can find.

But if your's LED's current is only equal to 40mA. In this case, you do not need a MOSFET.

You can use any small-signal BJT with the base resistor around 470Ω

I got so sick of how fiddly BJT's could be that I looked at Mosfets as a gift from above. But i may look at one anyway. Thanks.

 

Or you could try something like this with your favorite IRF610 and not so much likable BJT's.

 

Or you could try something like this with your favorite IRF610 and not so much likable BJT's.
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Yes. that makes sense. I'm not sure why using a transistor to fire the mosfet never occurred to me. I going with I'm tired. Thanks.

 

I would buy the IRLZ44N anyway, just to have a good logic level MOSFET on hand.

To drive 40mA at 12VDC you can use any NPN or N-MOSFET. I think the 2N3904 NPN is the cheapest alternative (and nice to have anyway), 100 pieces for 1 dollar: https://www.ebay.com/itm/100pcs-2N3...nkw=2n3904&_from=R40&rt=nc&_trksid=m570.l1313

 

There is just something wrong with using a part capable of 47A for 40mA.

Edit: Not to mention using a 10W LED at less than 1/2 W.

Bob

 

There are two parameters that identify a logic-level MOSFET.

One is the gate-source threshold voltage, Vgs(th).
Its maximum value will likely be 2V or less.

The other is the Vgs used to specify the MOSFET on-resistance.
It should be rated at the Vgs you have to turn it on as a switch.

 

Graphs on a datasheet are for a "typical" device that you cannot buy. The one you get might be much less sensitive or much more sensitive. Look at the printed Minimum and Maximum spec's instead and design the circuit to work with any spec's in that range.

The "threshold" voltage of a Mosfet is again a range of voltages, some are less or more sensitive. At the threshold voltage the Mosfet is barely turned on (useless) and is actually almost turned off.