Favorite MOSFET's - Page 1
Forum section: electronics / projects

author: raptor1956
author_rank: Frequent Contributor
timestamp: July 11, 2017, 04:48:41 am
content: I'm working on a project, just started actually, and I have a need for several PWM circuits to control the effective current in three voltage ranges: 10VDC-15VDC at 5A, 13VDC-20VDC at 5A, and 20VDC-30VDC at 5A. Ideally the MOSFET's should have as low an RdsON as possible but a tiny improvement in RdsON wouldn't warrant a significant price increase. So, what our your favorite MOSFET's, both N-channel and P-channel, that would fill this requirement and bonus points for 5V control and operation without need of a heat sink. I should add that the only inductive load is a 200mm or 230mm fan so there should be only a little inrush for the 10-15 range. The items to be controlled include: Peltier modules and nichrome heater (10-15VDC) running at 1A to 5A, 4S battery charger (13-20), and 6S battery charger (20-30).Brian

author: tivoi
author_rank: Contributor
timestamp: July 11, 2017, 04:53:49 am
content: 20-30V 5A , i recommend irfz34n, irfz44nsmal size irlu024nhttps://www.infineon.com/dgdl/irfz34n.pdf?fileId=5546d462533600a40153563b133f2200https://www.infineon.com/dgdl/irfz44n.pdf?fileId=5546d462533600a40153563b3575220bhttps://www.infineon.com/dgdl/irlr024n.pdf?fileId=5546d462533600a4015356694bf6265b

author: alsetalokin4017
author_rank: Super Contributor
timestamp: July 11, 2017, 05:11:43 am
content: IRF3205 is my favorite mosfet for lowish voltage.And a second vote for IRFZ44n

author: georges80
author_rank: Frequent Contributor
timestamp: July 11, 2017, 06:28:37 am
content: Just put your requirements into the various filters at digikey or mouser and there's lots of great modern fets.Most of my stuff is SMT. AON7246 is a pretty decent device with low rdson and 60V capability. A very nice lower voltage FET (with very low Vgt) is the CSD16340Q3. AON7520 is not half bad either with 30V max (less than 2.1 milliohms with 4.5V gate drive!). These are all n channels. The last two devices can easily switch 5A (PWM) without any heatsink - just soldered to a minimum area of PCB copper as part of the footprint. Easy to reach 10A with thermal vias under the main pad and the PCB mounted with some double sided adhesive thermal tape to the case/housing.Anyhow, use the filters and search the above websites, lots to choose from. I haven't used to220 style fets for many years now. The beauty of new SMT FETs is that they have a great thermal path from junction to solder pads and no pins/leads to add additional resistance or inductance.cheers,george.

author: Crumble
author_rank: Regular Contributor
timestamp: July 11, 2017, 02:48:43 pm
content: My favourite MOSFETs are usually dictated by availability. I have a stock of IRF2807s and HUF75345P3s, both of which seem to have been a surplus or at least a bargain. The HUFs have quite extensive datasheets though, and I prefer them when I actually use its full potential. Their datasheets states the safe operating area for lineair use and includes a Saber and PSpice model of its parasitics. It also shows a model with 6 thermal junctions/capacities. I don't use this data, but sometimes it's important to have a complete datasheet and in this respect these units win. I think it might be an industrial spec component or so. If there's still an actual electronics shop in your neighbourhood, or better yet one that is closing down, do visit it because sometimes it has parts that are considered obsolete or surplus and it is these I use for hobby. When designing for production (which I don't) this is terrible, but when you don't know what you're going to make it's great!

author: Siwastaja
author_rank: Super Contributor
timestamp: July 11, 2017, 04:20:36 pm
content: By asking "favorites", you get ages old parts with inferior specs, most often.Just use parametric search on your favorite supplier and pick a fet based on:(a) meets your specs(b) is cheap(c) availability numbers seem good

author: raptor1956
author_rank: Frequent Contributor
timestamp: July 11, 2017, 05:33:46 pm
content: I have gone to Digikey and 'tried' the parametric search, but I do no like the way they have that laid out. In my case I'm particularly interested in the lowest RdsON and the column for that is confusing as hell. They appear to list values for RdsON that are well below 1mOhm which seems highly unlikely to me. I guess using parametric searches a lot helps, but I confess searching for MOSFET's using it is something of a struggle. Almost any one is good for a couple amps, but by the time you get to 5A the I^2R really begins to become borderline for operation without heatsink and I'd prefer to not install them if possible.Brian

author: georges80
author_rank: Frequent Contributor
timestamp: July 11, 2017, 06:04:29 pm
content: ^ digikey. I have no issues using their parametric search. And why do you think that sub milliohm FETs are not likely? Plenty exist, especially for n chan FETs. Technology has improved dramatically versus old irfz44 etc devices. There's some impressive SMT devices out there.The 1st post I made showed a nice fet with 2.1milliohm rdson at only 4.5V gate drive (less at 10V). It even has pretty decent low rdson at 2.5V gate drive.Many FETs will be barely turn on with 4.5V gate voltage. You need to sort through the various parameters that you find important (not the least the gate capacitance and Qc depending on your operating frequency and driver capability).There's more to a FET choice than just rdson...Use the parametric search to meet most of your goals then pull up the datasheet to validate the parameters based on your operating requirements.cheers,george.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: July 11, 2017, 10:03:08 pm
content: Quote from: Siwastaja on July 11, 2017, 04:20:36 pmThe above posts are direct illustrations of this.Old parts are fine if you don't have concerns about switching losses or circuit size. They're also usually cheaper!If you need the utmost in efficiency, switching speed, size and so on, a search will find lots of lovely newer parts for all those ranges.To that end, I'll throw in another crappy classic: the '3055. No, not the 2N kind; it's also a MOSFET number that's been genericized, usually landing around 40V and 5A rating (so, roughly an IRF540), in SMT package. Manufacturers put their own prefix on, so, MTP3055, NDT3055, RFD3055, etc...FYI: for low voltages, MOSFETs rated <=20V have a particular advantage: their channels are "short". If you closely compare datasheets (say a 20V against a 50V part), you'll find:- Rds(on) has a much lower tempco- Vgs has a lower max rating (often 8-10V, beware!)- Gm is much higher (usually combined with somewhat low Vgs(th), making 3.3V logic levels accessible, even down to 1.5V for smaller parts!)(Gm is transconductance, the gain, i.e., you get so-and-so change in drain current from a this-and-that change in gate voltage. Higher Gm means more turning-on from less gate voltage.)From 30 or 40V, on up, Rds(on) tempco is fairly typical (at higher and higher voltage ratings -- channel lengths -- it tends towards the tempco ofdoped silicon, for obvious(?) reasons). Likewise, Vgs(th) and Gm are pretty typical, so that 5V drive is cromulent for "logic level" parts, and 10-15V drive is best for all types.As voltage rating goes up (100V+), the body diode performs worse and worse: t_rr and Qrr keep on rising (hmm, almost proportionally, come to think of it). Not usually a problem, but something to keep in mind for certain circuits.At higher voltages (200-600V), the optimal MOSFET design fundamentally changes (SuperJunction type), which is visible in the capacitance vs. Vds plot: capacitance drops out almostentirelyabove about 20V. Some (usually Infineon?) will show a slight rebound in capacitance, at higher voltages (100V+), too.Before the SuperJunction process was introduced, MOSFETs used to get proportionallyworseat higher voltages: Rds(on) went as the square of the voltage rating! This made >600V MOSFETs prohibitive to use in many applications. Older types will show this; not to say they're utterly undesirable, as they may still be quite cheap (IRF/IRFP parts come to mind).But among newer parts, if you need, say, a 1200V MOSFET, you'll get a damned good deal with one, and a damned fine device to boot (they're dangerously fast!).Tim

author: raptor1956
author_rank: Frequent Contributor
timestamp: July 12, 2017, 05:01:04 am
content: Thanks for the feedback -- the AON7520 looks great for 2 of the 3 applications but a bit marginal for the third. I guess it makes sense that lower voltage units can have lower RdsON values but I had no idea that there were in fact some that were sub mOhm -- pretty amazing really. Also, the really low RdsON at even 2.5V GS is pretty amazing though in my application the 4.5V value of 2.1mOhm looks pretty sweet -- again, thanks for the tip...I've used the parametric search function before and with some components is pretty straight forward and self explanatory, but I guess seeing the sub mOhm values for RdsON really threw me. I guess I need to spend some time figuring it out...Brian

author: T3sl4co1l
author_rank: Super Contributor
timestamp: July 12, 2017, 06:17:21 am
content: If you start with the blank however-many-thousands of MOSFETs Digikey has in their catalog, yes, you'll see, well, literally all possible values of Rds(on).And yes, they really do go down to fractional milliohms: those are most likely the low voltage parts used for battery protection. Pretty impressive what you get with a mere 6V D-S rating: imagine the transistors from 74HC logic, say (which is rated for 6V), but occupyingan entire die for one transistor. It's fast, high gain, and ridiculously conductive.Hey, don't be afraid to make a curious selection and see what lies beneath. That's exactly why I know the above...Tim

author: floobydust
author_rank: Super Contributor
timestamp: July 12, 2017, 06:49:49 am
content: I find MOSFET datasheets full of hype and "specmanship", competition is fierce and the industry seems to have fallen into a marketing spin.Two examples:D2PAK rated 195A (package) 340A continuous, curves to 1,000AInfineon AUIRF1324Snote "Calculated continuous current based on maximum allowable junction temperature. Bond wire current limit is 195A. Note that current limitations arising from heating of the device leads may occur with some lead mounting arrangements. "D2PAK 7-pin rated 310A continuous, SOA curve to 1,800AFairchild FDB0165N807Lnote "Computed continuous current limited to Max Junction Temperature only, actual continuous current will be limited by thermal & electro-mechanical application board design."So the specs are"computed" now. And totally outer space IMHO.I like the power dissipation "300W" but oh mounted on a PCB 40°C/W so it's 3.8W actually.So when you click on Digikey's parametric sort, remember it's marketing numbers.

author: KL27x
author_rank: Super Contributor
timestamp: July 12, 2017, 07:32:45 am
content: This the way they been doing it as long as I have been in the game.I don't know why they even have to list amps, at all. Other than the peak/surge. What I wanna know is rds on and the power dissipation of the package.

author: Muxr
author_rank: Super Contributor
timestamp: July 12, 2017, 07:37:39 am
content: Well and the threshold voltage.I find narrowing down MOSFETs easier than finding the right OpAmps. Especially instrumentation OpAmps for precision applications. You really can't tell them apart until you dig into the datasheets, and the info is spread out and laid out differently even for amps from the same manufacturer.One thing I found useful is going to the manufacturer's website. Like I will checkout the major manufacturers and their pages usually tend to have better search and sort criteria.

author: vealmike
author_rank: Regular Contributor
timestamp: July 12, 2017, 12:42:10 pm
content: For low RDS, I don't think you can beat the direct-FET packaged from IRF. The clever packaging means low value parasitics too. Not cheap though.