5U4GB anyone? (I am kidding I do not have any of these.Power MOSFETs enable a huge range of electronic systems, specifically in situations where BJTs are not useful or efficient. 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. Of course there are plenty of old datasheets around with the Hexfet name.) But IR has been swallowed up by Infineon and I do not think they advertise them with that name for quite a few years. But I do not know if you have the few mA of drive current for a bipolar transistor.īTW 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. 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. Not all MOSFETs have this protection, and the added diode reduces spike voltage and noise. It is true that antiparallel diodes across the inductances may not be absolutely needed when using avalanche protected MOSFETs. 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 didn’t know about the impracticalities of its can. I will look at your suggestions when my store of IRLU2905 is empty. 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. In that diagram I also use R-R ladders so that the switching speed is lowered some due to C gs only, to avoid too much EMC. I also always ensure that Rds on is appropriate with the driving voltage and the parameters of the MOSFET. That’s one of the reasons I am now testing Fritzing and Ke圜ad, where one of my criteria is to which degree the tool should not become a hobby per se. iCircuit didn’t have any symbol with that diode/zener inside, how much I disliked that, I had to make a note about it. 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)”. When I work here alone, and don’t even have a parts list, just yellow notes, comments come in handy. I have of course always used diodes when switching inductances. 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.Īlso…see this: Electronics Area – 4 Sep 19 I do not know what is the load current for your MOSFET. Suitability depends upon the load current for the MOSFET. EDIT: The 2N7002 is sort of on the low end of what you would want. The IRLU2905 for driving a relay is over-overkill.ĢN7002 in SOT23 comes to mind as being a good reasonable choice. You could use something smaller if you want to do so. There are SOT23 MOSFETs with Rds < 0.05 ohms. If you are driving relay coils with 5V 12V or 24V, a SOT23 size MOSFET should be very comfortable doing that. What is the gate drive voltage for the MOSFETs?ĭo you have antiparallel diodes across the relay coils to clamp the reset voltage? What is the supply voltage for the relay coils? (5V or 12V?) Well I see what I think are several MOSFETs but that schematic is difficult to read.Īre the MOSFETs all switching relay coils? That is likely due to it not being such a great transistor package. If you encounter difficulty finding an Ipak footprint, it could be because it is not so popular.Is it a linear regulator transistor or a switching regulator? Will you heatsink it? Why are you choosing Ipak? IMHO it is not such a useful transistor package.You will smile when you easily fit the transistor into the footprint which you have properly designed. We on the forum will help steer you if you run into problems with the footprint. The transistor datasheet should have the necessary information. Why not make your own footprint? It is not difficult. Experience says: Put in the care now instead of after you get your boards.Without that care, you will damage the MOSFET. (Except that TO220 came before D2Pak and Dpak came before Ipak.) When the time comes to plug an Ipak MOSFET into a TO220 footprint, you will find the lead bending will require a lot of care. Ipak is through hole version of Dpak, while TO220 is through hole version of D2Pak. Ipak is significantly smaller than TO-220.
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