I have seen several posts, indication there is a difference between mos fet transistors (digital or analog). I have tried to determine this, but have not been very successful.
I just got some irfz44n, and can't tell if they are digital or analog. I of course want digital.
Thanks in advance for any suggestions.
Every transistor and fet is analog.
However, mosfets are very good at switching on and off large currents, so they are used for that.
The IRFZ44N is 'on' with a gate voltage of about 9V. That is for most mosfets the case. For the Arduino you need a 'logic level' mosfet. Those are already on at 5V.
Search on Ebay for: logic mosfet
If the voltage and current is what you need, they can be used.
When switching a current of 1A, it is no problem to use a 20A mosfet for that.
Or take a look at the www.sparkfun.com website and search for mosfet, they have a nice selecting components.
A MOSFET is both digital and analog.
Well, strictly speaking, it's analog.
In simplest terms a MOSFET can be thought of as a variable resistor where the resistance is controlled by the voltage difference between the Gate and the Source terminals (known as VGS). As the VGS rises it approaches what is known as "saturation". This is where the resistance of the MOSFET pretty much at its minimum. It can be thought of as fully "On" at this point.
When a MOSFET is used as a switch (in digital circuits) it is basically in one of two states - "off", where the VGS is at minimum, and thus the resistance is at maximum, and "on", where the VGS is in saturation, and the resistance is at minimum.
When being used in an analog circuit most of the work is done in the region between "off" and saturation. This is known as the "linear" portion of it's characteristic curve.
A characteristic curve is an important part of a MOSFET's description. It describes the relationship between the voltage across the MOSFET (VDS) and the current flowing through it (IDS), which is in effect the resistance of the MOSFET (Ohm's Law), at different VGS voltages.
A typical curve might look like this:
You can see how as the gate voltage increases the current also increases for the same drain-source voltage.
Well, if
The IRFZ44N is 'on' with a gate voltage of about 9V.
, I guess I have a few paper weights. LOL.
I will try the
Search on Ebay for: logic mosfet
. I just want a few for general inventory (hobby). Anyone have a favorite that will handle about 2 amps?
Thanks for the info.
If they are used for digital, you turn them full on & full off.
If they are used for analog, you bias them and operate them in their linear region.
That part is intended for switching
Unfortunately it is not a "logic level" device and is intended to have its gate switched at 0-10V levels.
To do that with an Arduino, you would typically use an NPN with its collector wired to the N-channel Gate, and emittor to Gnd. The NPN base would be pulled up to +5 so the NPN would be on pulling the Gate low and keeping the MOSFET off. When the arduino finished waking up, it would pull the NPN base low, letting the Gate float, and a pullup on the gate to +12 would turn it on.
Not being familiar with FET transistors, I find it hard to decide which ones to use with the arduino 5 volt signal, for switching.
I would just like to know a general purpose N channel FET to work with the arduino output, that can handle 2 amps or so.
I have done google searches, without learning. Any advice is appreciated.
Hit the parametric search facilities of your favourite supplier.
BTW, 2A is nothing to a MOSFET. As a result, finding one rated at that low a current in through-hole is not a simple matter.
Still, if you like higher currents, here's a good meaty one (not through hole, but big enough to be simple to solder):
35A current, 22mΩ at 2.5VGS, 60V.
The FETs you already have can be used by you in a 5v system. In the data sheet Figure 1
you can see that it can draw 10 amps when the gate voltage is at 4.5 volts. Do not use them as paper weights. The typical threshold voltage Vgs(vt) is about 3v, so 5v on the gate can get 25 amps through the drain to the source, as shown in Fig. 1, typical output characteristic. Test one device that you already have. It may be good enough for your experiment. If it is too weak test more from your stock until you find one with a low enough threshold voltage to give "typical currents" of 25 amps.
retrolefty has often recommended this...
http://forum.arduino.cc/index.php?topic=49993.msg360084#msg360084
Another recommendation...
http://forum.arduino.cc/index.php?topic=147149.msg1105768#msg1105768
retrolefty has recommended logic level mosfet type RFP30N06LE .
in that first link. But his use of the word "saturation " is wrong. Replace his word saturation with "linear region".
SATURATION REGION of n-channel MOSFET
Here is the definition of saturation : the drain-source voltage is more than the gate source voltage minus Vt.
saturation : Vds > Vgs - Vt
for example of saturation
Vds = 20v
Vgs = 5v
Vt = 3v threshold voltage
20 > 5-3
LINEAR REGION of n-channel MOSFET
the drain-source voltage is less than the gate source voltage minus Vt
linear : Vds < Vgs -Vt
example of linear region
Vds = 0.1v
Vgs = 5v
Vt = 3v
0.1 < 5-3
The word Saturation is used in the opposite way compared to npn bipolar devices, leading to confusion.
They are all analog and they are all digital transistors.
Wow, the more I learn the more I don't know !
For drivers for the arduino, N channel mos fet, 2 amps or more, cheap, what are the first 5 choices? Is my IRFZ44N anywhere in the first 5 ?
I find them at digikey using their filtering:
n-channel mosfet
select fets single
select in-stock
logic level
thru hole
This yields about 20 pages.
Click on left arrow under Price.
Go down the list until you get past the 1000 min buuy qtys.
Look for parts that are Low Rds, Low Gate Charge, Low input capacitance.
This one for example
looks pretty good:
VGS = 4.5 V, ID = 10 A 33mOhm Rds
For a few pennies more, these 2 look good too and have lower Rds but have higher Input Capacitance so may switch a little slower.
IRFZ44N is 9v
IRLZ44N is logic level
Try a power transistor like the Tip41... i never read your upper voltsge limit though .
The question about Digital versus Analog FETs will be be discussed now. In my previous post I said that MOSFETs can be used for digital or analog. More importantly, there are three voltage bias regions of n-channel MOSFETs:
Saturation region
Linear region
Cutoff region
The Drain, at constant gate voltage:
Saturation is providing a "constant current source" from the Drain.
Linear is is providing the Drain as a resistor-like current path.
The Gate, at constant drain voltage:
Saturated currents vary with the square of the Gate voltage
Linear currents vary in a linear way with Gate voltage
jackwp said he wants digital qualities from the MOSFET. The load for a digital circuit is best if it is a complementary MOSFET. That is called CMOS. A digital gate uses an n-channel and a p-channel MOSFET for good efficiency and simplicity. But jackwp may want to use a resistor for the load of a digital MOSFET circuit. That is good also, but less efficient for power dissipation than CMOS. In the olden days that was called resistor-transistor logic (RTL).
Jack,
Now that you have had your class in FET/MOSFET technologies,,,, Go to e-Bay and get some BSS338's, or if you have fat fingers like me, some 2N7000's,,, or you can get some 2N2222's or 2N3393's or just about any small signal NPN bipolar junction transistors to use as Gate drivers and go back to CrossRoads' post.
It ain't rocket surgery, you don't have to be exact unless you are an efficiency freek. Have fun, tweek it until it works or smokes and then try again.
Gig 'em Aggs, or Hook 'em Horns (if you must, ugh).
Ebay seems not to have any BSS338 . I did a search. Is that a typo?
jack,
STP40NF10L
10 of them for about $20
reasonable
they're very low "on-state" ohms
BTW - It's not "logic" vs "analog", it's "logic level" vs everything else.
"Logic level" means they get turned on right with a logic level ("5V") voltage (the others require more, much more.)
Thanks, Runaway, I am slowly catching on with all the help given on the forum. I tried again to order some FETS for general use, and just oredered these http://www.ebay.com/itm/250795972359?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2649. $0.92 each in lots of 10.
Any suggestions as to whether they will be of general use or not?
Why such an expensive part?
I think this would do the job too, just 52 cents each vs over $2 each.
And they have lower input capacitance so they'll switch faster.