N-Channel Mosfets with the I/O

Hello I just got some parts off of ebay, the part number is: IRFZ44N IRFZ44 MOSFET N-Channel 49A 55V

So I know that when using leds that you need to use resitors to keep the I/O from drawing too much power, So is the same thing applicable when using Mosfets? If so do you know about how much of a resistance I would need in order to keep the I/O safe?

You are correct, The mosfet gate is like a capacitor and will draw a large amount of current when turning on (and provide it when turning off). The current at the arduino digital pin should be limited to stay under its safe operating current (from the datasheet).

If you wanted to limit the current to 30ma (safe for arduino) for example 5v/0.030a = 166 Ohms.

Besides that. The mosfet you mentioned IRFZ44N is not a logic level device. The gate voltage should be over 10 volts to fully turn on. It will be only able to handle a fraction of its normal current at 5v gate voltage.

take a look at the datasheet differences between the irfz44n ( standard level) and Irlz44n ( logic level).

http://www.irf.com/product-info/datasheets/data/irfz44n.pdf

http://www.irf.com/product-info/datasheets/data/irlz44n.pdf

If you are driving the FETs with the Arduino, add a series 150 ohm resistor to the gate. IRFZ44N is not a logic MOS FET. .

You want to search the Arduino forum on IRFZ44 as its not the best choice.

Ideally go for the Logic Level Mosfets such as a FDP7030 which also has a low On resistance.

For most power mosfets its suggested you use around 220 ohm as a base resistor and a 10k+ from base to ground to avoid the mosfet turning on in error conditions. Again plenty of examples in the forum.

So if you were to suggest a Mosfet that I could use on a logic level what would be your suggestion? I need one that will operate at a minimum of 20 amps but other than that, voltage wise Is pretty flexible probably 12 volts minimum.

With a 20 amp current you would need a pretty beefy MOSFET. Less than 0.002 ohms rdsOn. Or a heatsink if you start going higher.

A MOSFET like the irlb3034 could maybe do.

The voltage does matter though, that MOSFET is good for up to 24 volts safely.

Depends what you need it for, different MOSFETs are good for different applications.

8ByteRemmargorp:
So if you were to suggest a Mosfet that I could use on a logic level what would be your suggestion? I need one that will operate at a minimum of 20 amps but other than that, voltage wise Is pretty flexible probably 12 volts minimum.

There are many 1000’s if not 10,000’s of MOSFETs available - the first thing to do is find
a good electronics supplier, rather than be limited to the few lines that crop up on eBay or
sparkfun etc. A good supplier will have a website search tool to search for devices according
to its specifications.

Key specs are voltage, on-resistance, gate drive voltage (ie <= 5V for logic-level, 10V for non logic level),
package type, total gate charge, n-channel or p-channel…

You might get more detailed help if you say what you are trying to switch and for how long you intend to keep them switched on for.

A PSU and load in excess of 20A + at +12vDC upwards is not your typical arduino diy use.

For anything other than very short term switching, you will be needing a psu rated at least 30 - 40 amps to avoid it overheating on full load.

20amps is indeed pretty beefy... Be prepared to handle some heat.

The IRFZ44N is indeed not a logic mosfet. If okay to drive 1A or so but above you want to fully turn it on. For that you need at least 5,5V... (So close...)

So I know that when using leds that you need to use resitors to keep the I/O from drawing too much power, So is the same thing applicable when using Mosfets? If so do you know about how much of a resistance I would need in order to keep the I/O safe?

FYI, I wouldn't agree with your wording above, because while there may be a grain of truth in your statement, the reason you use resistors with leds is not to prevent the I/O from drawing too much current , but to avoid burning out the led the instant you turn on the power. Most leds are rated for 20 mA. The arduino I/O is rated for 40 mA, but if you connect a led directly to an I/O pin, it might draw enough to burn out the led. I can't for sure when that would happen, not having tried it myself, but I think it's a true statement to say the reason you use resistors with leds is to protect the leds, not the I/O.

raschemmel has a good point.

I would say that using an resistor to limit current for an LED is to protect BOTH the output and the LED. The resistor must me chosen to limit the current to a safe level for the weakest part of the circuit.

If you had an led that allows forward current of greater than the arduino can provide then the resistor must be chosen for the pin limit, not the LED limit.

If the pin can source/sink more current than the LED will allow the the resistor must be sized to stay under the LED safe limit.

AOI510 http://www.digikey.com/product-detail/en/alpha-omega-semiconductor-inc/AOI510/785-1487-1-ND/3603498 Will need heatsinking with 20A. Power dissipated = I^2 * R = 20V*2 X .004ohm = 1.6W