Hi there
I'm about to control some LED strips (12V, 1A summed up) and want to use a MOSFET. Since I don't want to use a 500V 100A type, there aren't any MOSFETs with gate-voltage around 5V. So what is the best way to control the MOSFET? I think the voltage regulator way is not the "correct" one. Should I use a resistor in series to the gate? Speed is not an issue at all.
Thanks!
What you need to look for is a "logic-level" MOSFET - this means its fully switched on when gate-source voltage is at 4.5V or higher. They are less common in TO220 package than "normal" 10V MOSFETs, but there are plenty.
For 1A the on-resistance should be less than about 0.3ohms to avoid needed a heatsink. On resistances of less than 0.1ohms are commonplace these days.
A 150ohm resistor from Arduino pin to gate is all that's needed to drive a logic level MOSFET and that's solely to protect the Arduino output from pulling/pushing too much current during switching.
PS a key thing to look for in datasheets is something like "Rds(on) at Vgs=4.5V" - this is a logic level device since the on-resistance is guaranteed for 5V drive. If the phrase "logic level" is missing and the only Rds(on) fugures are for Vgs=10V, its not logic level.
PPS: To drive a non-logic-level MOSFET you can use a level-shifting circuit with an NPN transistor, should be various examples on the site if you search.
You are not looking for a MOSFET with a gate voltage of 5v. You are looking for one with a threshold voltage of <5v.
The quoted 'gate voltage' is usually either the point at which they test the 'on resistance' (generally the point when the mosfet is fully on), or it is the 'threshold voltage' which is the point at which the mosfet starts to conduct.
Simple summary, any mosfet with the following will suit your needs:
Just an an example, here is a list of 103 N-Channel Mosfets which Farnell sell which would suit your needs:
Long URL
Logic level MOSFETs, perfect!
I found some in SO-8 package, 4pin drain, 3pin source and 1 pin gate. Is it common to connect all the same pins together? This is the only way my head would allow me to accept to let such high current throug those small pins 
Just out of interest, how do you know 150ohm would be right?
No no no - the threshold voltage is not the spec to look at for a switching power MOSFET.
The threshold voltage is where the device just starts to conduct (typically in the microamp range). This is not interesting.
You need to know that the device is cut-off fully at 0V (always true for enhancement-mode power MOSFETs), and that its fully switched
on when you drive the gate high. This means looking at the Rds(on) figure for the Vgs in question.
Many people make the mistake of thinking that is the threshold voltage is quoted as 2--4V the device is on at Vgs=5V - its isn't, all
you know is that the devices switches fully OFF at 2--4V.
For logic level devices you usually find the Vthr is about 0.5 to 1.0V.
Looking at the graphs in the datasheet you'll see one that plots gate charge against gate voltage - it has a big plateau in it, and this plateau is where the device is properly switching on (these graphs are typical values, not guaranteed values). This value of gate voltage will be somewhere between the Vthr and the Vgs quoted for Rds(on) ratings. For good switching you ideally want the plateau at about half the gate drive voltage (this means switch on and switch-off are symmetric in terms of timing, leading to most efficient switching).
Most 10V gate-drive devices show a plateau around 4 to 6V. Logic level devices show one around 2 to 3V.
So to reiterate when using a power MOSFET as a switch ignore the Vthr parameter, it doesn't tell you anything useful that the Rds(on) and plateau voltages don't.
Quoted threshold voltages are great for filtering of devices in lists.
By glancing down lists of MOSFETS, you can immediately see which devices will definitely NOT be suitable, as the VGT is well above what you are looking for. From there you can examine the ones that MIGHT be suitable in more detail to find the RDS_ON at the voltage you will be switching at to find the most suitable for your application.
These work great with the arduino, provided you are after P-channel. Digi-key part number FQB27P06TMCT-ND. I'm using them in my own project with arduino.
Thanks for all your help, guys! I fell in love with the FDS6690 (HTTP 301 This page has been moved), since it is logic level and cheap.
Since I'm always struggling with resistor values (what goes further than resistors in series with LEDs), I'd like to ask you, how do you know 150ohms is right? What do others think? 
Thanks
A MOSFET's gate is just like a capacitor. When power is applied to it the capacitor charges up.
That draws current. Where the voltage differential is greatest (applied voltage is 5v, gate voltage is 0v) the current is greatest. We need to limit that current so it doesn't exceed the 40mA of an Arduino IO pin.
150 ohms limits the current to 33.333333mA - a good value that is well within the 40mA limit, and yet allows enough current through so the gate capacitor charges fast. Too large a resistor and the gate will take too long to turn on. Too small, and we'll draw more than 40mA.
33.3333mA gives a little bit of a safety margin to cover the inaccuracies in resistor values, and is also a common value.
BTW, the 33.3333mA was obtained with ohm's law: I=V/R = 5/150 = 0.0333333.
Thank you, perfect! So I'm ready to build and test