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Topic: Best mosfet for switching DC from 5v Arduino pin. (Read 14 times) previous topic - next topic

mwhens

For home automation I want to switch some DC current ranging from 0-60v.
Some 48v led series, strike plates, and allot more.
I want to build some universal switching boards that I can use for all DC switching that I need.
It needs to switch fast enough to use PWM from an Arduino pin. And works perfect on 4-5v.
For 220v AC I will use solid state relays (ebay.com).

I ones used a mosfet IRF540N (old one) for switching fans and leds, but I want to choose the best available, and also more watts.

Someone advised me this one...

IRLZ34NPBF rom International Rectifier
55V, 30A, max.68W
http://www.irf.com/product-info/datasheets/data/irlz34npbf.pdf

Rds On (Max) @ Id, Vgs: 35 mOhm @ 16A, 10V
Vgs(th) (Max) @ Id: 2V @ 250µA
Gate Charge (Qg) @ Vgs: 25nC @ 5V
Input Capacitance (Ciss) @ Vds: 880pF @ 25V

But the 68Watt is a little low, I would like a heavy mosfet.
On Digikey I see lots of heavy mosfets, But I'am not sure if they work wel with an arduino pin/5v. Or if they switch fast enough for PWM?
I selected some...


STP60NF10 from STMicroelectronics
http://www.st.com/internet/com/TECHNICAL_RESOURCES/TECHNICAL...046750.pdf
100V, 80A, max.300W

Rds On (Max) @ Id, Vgs: 23 mOhm @ 40A, 10V
Vgs(th) (Max) @ Id: 4V @ 250µA
Gate Charge (Qg) @ Vgs: 104nC @ 10V
Input Capacitance (Ciss) @ Vds: 4270pF @ 25V


or


IRLB3036PBF-ND from International Rectifier
http://www.irf.com/product-info/datasheets/data/irlb3036pbf.pdf
60V, 195A, max.380W

Rds On (Max) @ Id, Vgs: 2.4 mOhm @ 165A, 10V
Vgs(th) (Max) @ Id: 2.5V @ 250µA
Gate Charge (Qg) @ Vgs: 140nC @ 4.5V
Input Capacitance (Ciss) @ Vds: 11210pF @ 50V


or


IRL3705NPBF from International Rectifier
http://www.irf.com/product-info/datasheets/data/irl3705npbf.pdf
55V, 89A, max.170W

Rds On (Max) @ Id, Vgs: 10 mOhm @ 46A, 10V
Vgs(th) (Max) @ Id: 2V @ 250µA
Gate Charge (Qg) @ Vgs: 98nC @ 5V
Input Capacitance (Ciss) @ Vds: 3600pF @ 25V


I will use a small transistor on the pins so it can give more than 20mA. But will these heavy mosfets work?
What are the disadventages of these heavy mosfets, I don't know allot about mosfets, Don't know anything about those 4 lines of specs like RDS, VGs, Qg or CISS.

AWOL

Unless you put a driver between the Arduino and the MOSFET, you should really be looking for "L" suffix (Logic) devices.
A 10V VGS isn't going to saturate with a 5V Arduino input, so your device is going to get HOT.
"Pete, it's a fool looks for logic in the chambers of the human heart." Ulysses Everett McGill.
Do not send technical questions via personal messaging - they will be ignored.

MarkT

Firstly you can usually ignore the current rating as power-dissipation is the limiting factor (without substatial heatsinking).

The key spec is the Rds(on).   Calculate the power dissipation for your load with P=I^2R.  For large currents you are likely to want a heatsink (say if the dissipation is more than 1/3 watt.)

Secondly beefy MOSFETs have high input capacitances.  Very high input capacitances.  You can drive the gate from the Arduino with a resistor to limit the pin's current to a safe level for the microcontroller (say 25mA max - 220 ohms).  However this means slow switching (many us) leading to a large power-dissipation pulse in the MOSFET while it switches.   For low to medium power loads at low to moderate PWM frequencies this is fine, but driving a high powerload at high frequency PWM this will become prohibitive.

Arduino default PWM is 1kHz or 500Hz depending on the pin, so this isn't too big an issue unless you change it.

If you want faster/more efficient switching you need a MOSFET driving chip to charge/discharge the gate capacitance quickly (drivers are usually 0.2 to 1A or so).  I've used a MIC4422 before which can drive pretty much any MOSFET hard from a simple logic signal.  These driving chips need proper decoupling (but can level shift from 5V to 12V to allow non-logic MOSFETs to be used)

There is one more issue you need to be aware of which is capacitive coupling between drain and gate.  For high voltage loads the voltage swing in the output can couple to the gate strongly enough to _require_ that the gate is driven by a low-impedance source (a few ohms) to prevent voltage spikes on the gate (these can damage the gate oxide and whatever is driving the MOSFET)

The more voltage and current being switched, the more important this is.  I would recommend for high current loads over 20V or so to always use a MOSFET driver chip to prevent this being an issue.  Also logic-level MOSFETs are more sensitive to this problem.
[ I won't respond to messages, use the forum please ]

mwhens

You mean I can't use one of these mosfets?
Are you sure, Vgs(th) (Max) is only between 2-4v.

retrolefty

#4
Aug 27, 2011, 08:07 pm Last Edit: Aug 27, 2011, 08:08 pm by retrolefty Reason: 1

You mean I can't use one of these mosfets?
Are you sure, Vgs(th) (Max) is only between 2-4v.


What you really have to do is read the datasheet for the specific device. Most have a graph showing source/drain current flow Vs gate/source voltage. For switching duty you want to select a device that will force the device to it's best Ron value with the 4.5 to 5 volt gate/source voltage applied. Most devices described as "Logic Level" will do that, but it's really on you to determine via datasheet analysis. Gate threshold value is a related spec, but doesn't define the complete situation as far as gate voltage Vs actual load being switched, Vs heat dissapation.

Also those very large MOSFETS have very large gate capacitance values putting demands on the device supplying the gate voltage. The arduino output pins are pretty husky but even they might struggle with the gate charging and discharging current requirements of those largest devices, this can 'slow' the mosfet switching time and result in higher heat dissapation even to the point of mosfet destruction if maximum rated current is being switched. Those hugh current rated mosfets are almost always better being driven by special MOSFET gate driver chips. So if your planning on trying to switch a 50 amp load on and off, you should research proper gate drive requirements to insure the mosfet stays in it's SOA, safe operating area.

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