I have an IRLR/U2905PbF hexfet transistor in an I-Pak (TO-251AA), see https://www.elfadistrelec.no/Web/Downloads/05/_e/lgIRLR-IRLU2905_E.pdf.
Is there any component I can start off from? I managed another one from TO-92, but I-PAK or TO-251AA give no search hits.
Packages_TO_SOT_THT:TO-251… several variants ?
Thanks, but I cannot find it while browsing symbol libraries. It’s worse: I can’t even find “TO-251”. I am soo new to this…
You want Q_NMOS_GDS, then assign this footprint to it.
Oh, I did not understand you were talking about the symbol. MOSFET would be the search key.
There are some in the libraries, but not at least the most common (at least in Europe) ones. But perhaps you can find one that fits. You can change the Value to your type then.
If not, there are generic MOSFET you can use, named Q_NMOS_GSD with a lot of variants …_GDS, …DGS, … depending on the gate-drain-source order.
You have then to assign a package to the symbol.
Thanks, guys! If I place this MOSFET based on Q_NMOS_GDS (1=G, 2=D, 3=S which is correct) and I try to do Edit footprint on it, it requires me to find something, which isn’t there. Wvat should I search for there?
However, I found a part based on TO-220 instead (Package_TO_SOT_THT:TO-220-3_Vertical) and made my way from there. I haven’t studied how TO-220 differs from IPAK/TO-251AA, but for now it’s probably ok. I’m making one or two boards only…
Hi, Aclassifier
Great. BobZ! I am using the IRLU2905 simply because it’s a fantastic transistor. I found it by searching around some years ago (when I retired), with no thoughts about the case whatsoever. I have never needed the current, but the 27 mOhm on I do fancy. An example is fig.2 at [1]. I have only been soldering my own one-of-a-kind boards. Now I wanted to make a nice PCB drawing, for two boards, and am going from iCircuit to KiCad.
I so much would wish for an I-PAK footprint that I could plug into my component! I guess, if it were there, it might be used by someone else as well…? If not, I might be stubborn enough to try - with some help - thanks!
Which other HEXFET with built-in zener and low ON resistance might you suggest? I also use TN0604, it’s in a TO-92. I used the generic FET for it, but found none with the correct pin numbers, so I modified it.
[1] My USB watchdog (and relay output) box Disclaimer: No income or no ads from my blog notes. Only expenses and fun!
Well I see what I think are several MOSFETs but that schematic is difficult to read.
Are the MOSFETs all switching relay coils?
What is the supply voltage for the relay coils? (5V or 12V?)
What is the gate drive voltage for the MOSFETs?
Do you have antiparallel diodes across the relay coils to clamp the reset voltage?
If you are driving relay coils with 5V 12V or 24V, a SOT23 size MOSFET should be very comfortable doing that. There are SOT23 MOSFETs with Rds < 0.05 ohms. Here is one small group:
Those are cheap and easy to solder. You could use something smaller if you want to do so. The IRLU2905 for driving a relay is over-overkill.
2N7002 in SOT23 comes to mind as being a good reasonable choice. EDIT: The 2N7002 is sort of on the low end of what you would want. Suitability depends upon the load current for the MOSFET. I do not know what is the load current for your MOSFET.
If you are driving the MOSFET gate with only 5V, you should use a MOSFET which has Rds (on) specified with drive of 5V or less.
Also…see this:
Thanks BobZ. I have of course always used diodes when switching inductances. When I work here alone, and don’t even have a parts list, just yellow notes, comments come in handy. One of the comments in that diagram goes like this: “All 4 TRANSISTORS TR1-TR6 are N-MOSFET HEXFET IPAK N 55V 36 A IRLU2905PBF Zener inside: enhancement mode 27mOhm on (ElfaDistrelec 70-085-70) (iCircuit symbol differs)”. iCircuit didn’t have any symbol with that diode/zener inside, how much I disliked that, I had to make a note about it. Also, iCircuit can’t make new symbols. That’s one of the reasons I am now testing Fritzing and KeyCad, where one of my criteria is to which degree the tool should not become a hobby per se. I also always ensure that Rdson is appropriate with the driving voltage and the parameters of the MOSFET. In that diagram I also use R-R ladders so that the switching speed is lowered some due to Cgs only, to avoid too much EMC. This is of course most needed when there is a lot of switching and long wires, as in my PWM control of LED lights for the aquarium. I will look at your suggestions when my store of IRLU2905 is empty. I didn’t know about the impracticalities of its can. Edit: Note there also is a reverse diode across the power supply to make adding an extra diode across the inductance not necessary, when there already is one inside the transistor. I tend to use schottkys for that.
It is true that antiparallel diodes across the inductances may not be absolutely needed when using avalanche protected MOSFETs. But I would prefer not to rely on that. Not all MOSFETs have this protection, and the added diode reduces spike voltage and noise. Actually if I can drive a relay with a 500 mA 40V transistor such as MMBT4401 I would generally prefer to do that because it is cheap and common. But I do not know if you have the few mA of drive current for a bipolar transistor.
BTW Hexfet is an old name (brand specific to International Rectumfriar 
) I think IR had the first practical power MOSFETs about 40 years ago and called them Hexfets. But IR has been swallowed up by Infineon and I do not think they advertise them with that name for quite a few years. Of course there are plenty of old datasheets around with the Hexfet name.)
The other thing I should have added: One of the best arguments to use a given device is because you have a bunch of them. 5U4GB anyone? (I am kidding; I do not have any of these.)
Yes, I would have added that extra diode of this were a board of the millions, so that I could later replace and select from a larger range of MOSFETs. Mail me if you want any 5U4GB. But my transputer boards are all gone. Sorry.
Just a follow up.
I tried to add a library of the IRLU2905PBF, pointed to from Digi-Key, from the Ultra Librarian (here), but following the recipe it turned out to contain a “Legacy” library which had “Invalid footprint specified” even after a “Migrate Libraries” in KiCad
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