thunderace7
New Member
Hi. I bought some IRF520/STP14NF10 transistors from the Picaxe store but, looking at the data sheet, I don't think they are logic level FETs. Can anyone confirm, please?
FETs
- Thread starter thunderace7
- Start date
inglewoodpete
Senior Member
While the IRF520 will work when driven by a PIC, it is not ideal and can't be switched on sufficiently to carry its rated current without a higher voltage driver.
This bit from the datasheet explains why it's not an ideal match for a pic.
Gate Threshold Voltage 2.0 ––– 4.0 V
It may not work at all when using a 3.3 volt device.
It takes somewhat more than the "Threshold Voltage" to turn an FET on fully.
Continuous Drain Current, VGS @ 10V 9.7A
It may work with a 5 volt device if you just need a little current but not if you need the full current
To get the FET's 9.7 amp maximum current, you need 10 volts on the gate.
Gate Threshold Voltage 2.0 ––– 4.0 V
It may not work at all when using a 3.3 volt device.
It takes somewhat more than the "Threshold Voltage" to turn an FET on fully.
Continuous Drain Current, VGS @ 10V 9.7A
It may work with a 5 volt device if you just need a little current but not if you need the full current
To get the FET's 9.7 amp maximum current, you need 10 volts on the gate.
neiltechspec
Senior Member
I have used a pair of IRL540's for controlling cooling fan speed - 20A at full speed. Been in use for years.
Numerous other IRL520/IRL540's used on other projects, all direct driven by PICAXE.
Numerous other IRL520/IRL540's used on other projects, all direct driven by PICAXE.
thunderace7
New Member
Picaxe store only stock IRF520 as a high power FET. I've ordered some IRLZ44Ns from eBay. Thanks for confirming what I thought.
lbenson
Senior Member
The ones I have like that make a convenient module. I snip off the IRF520 leaving as much of the pins as possible, and solder on IRL520 or equivalent. Pretty easy to do.
erco
Senior Member
FYI, I just ordered 50X IRLZ44Ns for $16 shipped, best deal I found. https://www.ebay.com/itm/264732733497
Most parts prices have doubled or better since Covid.
Most parts prices have doubled or better since Covid.
lbenson
Senior Member
FWIW, I've found these logic level MOSFET modules to be useful: LL MOSFET modulesI recently receive some MOSFET breakout boards, fitted with IRF520.
in addition to prices shipping has significantly increased, seldom free.
Technoman
Senior Member
Fitted with two D4184 (datasheet : Alpha & Omega semiconductor D4184), wired in parallel, each rated at 50A max, giving his best at VGS=10V. Rated at a lower current, 15A, that would probably do the job.
From that datasheet, with Vgs 4.5V and Id of 15A the internal resistance is 8.5milliohms versus 6.7milliohms at 10Vgs and Id of 20A. Probably OK to use a single D4184 FET at 15A and drive from a nominal 5 volt source. 15A dissipation would be I * I * R or 15 * 15 * 0.0085 = 1.91 watts.
Technoman
Senior Member
The circuit diagram : Diagram. They probably added a second MOSFET to lower the rDS(on) at VGS=5V, although there is nothing to balance the current in between.
Back to the IRF520 breakout board : you can read here and there that the board can handle up to 5A driven by a microcontroller (Ard..., Rasp...,...). According to a datasheet (STM), at VGS=5V, the maximum ID is 3A... Given as suitable for a 5V microcontroller, some wrote it might also work with 3.3V... I think this is not a fair information as some people could have some issues while using heavier loads.