Mosfet for LED strips

Using Arduino General Electronics
1

Hello

My question regards Mosfets. I need one to power a strip of LEDs which will draw more current than an Arduino can handle so I will use a DC power plug to power the strip and simply control it from my Arduino.

I've been googling around and am unsure what sort of mosfet to purchase. I don't understand the data sheets. I know I need to purchase one that can be controlled by 3.3v I read that it was recommended to purchase an L series Mosfet as they are designed for micro-controllers? Not sure.

As an aside is it best to use a Mosfet or should I use a transitor I was leaning towards a Mosfet as I read they do not give off as much heat saving energy that way. I'm going to be using 12v and between 0.6a and 1.5a to give you an idea of the power being running through.

So my questions are:

What parameter should I be looking for in an Mosfet's datasheet. What is the specification called that triggers whether or not to allow current through? Where will it say what voltage is needed to be applied to gate pin? (Vgs???)
What are the parameters called that tell me what the max voltage and ampage that the Mosfet can handle?

Thanks in advance

2

If you really mean 3.3V rather than 5V the choice is more limited (except for surface mount
devices).

I found an expensive one that works with Vgs from 1.8V up: http://uk.farnell.com/vishay-siliconix/sup85n02-03-e3/n-channel-mosfet-20v-85a-to-220ab/dp/1254171?min=110007502&selectedCategoryId=&categoryId=700000043507

What you need to look for is the Rds(on) value for a given Vgs. If the Vgs value is 3.3V or less, then
that guarantees an on-resistance as quoted. If Vgs is less than any quoted, you cannot rely on the
thing being properly on. The Vthr (threshold voltage) should be about 1/3rd of the Vgs value, as that's
the turned-off point. Vthr has a large variation, expect to see values quoted as 0.5--1.0V for a logic level
device.

For 12V LED strips driven from 3.3V strongly consider using a MOSFET driver chip and a standard
(not logic-level) MOSFET as the choice is much greater.

3

This one from Sparkfun is also pretty handy.

4

That's two devices, and neither are rated to work from 3.3V.

5

Sparkfun Claims it can work at 3V. I've not tried it. I assume it's much less happy at 3V since I agree... even the curve in the transfer diagram shows that.

6

You could look at using a P MOSFET to switch +12v to the string. You would then use an NPN transitor to turn the MOSFET on. This would work at 3.3v on the base.

Weedpharma

7

IRF3708PBF is pretty good at 3.3v (see the chart in datasheet)... and it's in TO-220.

There aren't many good MOSFETs that work at 3.3v available in through-hole packages (in SMD packages, there are tons of options). There's also some TO-92 one that digikey sells that's good down to 1.8V on the gate, but it's low current.

As it happens, I sell MOSFETs on breakout boards - SOT-23 and larger 4-channel boards

8

You mean the "typical" chart? They are not a contract, and there is a lot of device spread on
threshold and plateau voltages (they creep with age for instance due to ion-migration in the
gate oxide).

The minimum and maximum values are the ones you can rely on.

9

It is simpler to use a transistor to booth the voltage used to
drive the FET with.
Dwight