My requirements are as follows
* Controllable at 0-3.3V (via MCP2307 I2C IO Expander)
* 500mA at VDS 5V continuous load, so 2.5W
Vgs(th) is 1V, so the 3.3V ought to be sufficient.
Hi,
During the weekend I got some great help re. transistors and MOSFETS. I hope I've now learned enough to dare select a MOSFET and use that in my design.
My requirements are as follows
* Controllable at 0-3.3V (via MCP2307 I2C IO Expander)
* 500mA at VDS 5V continuous load, so 2.5W
* VDS up to max 12V i.e. ~210mA.
* Preferably no heat-sink needed.
* SMD
* Low-side switching.
I'm currently looking at the IRLL110TRPBF, N-Channel for low-side switching.
Alternatively the SQ1431EH for high-side switching (would of course need extra control circuitry as shown in this post by @Spec.
Vgs(th) is 1V, so the 3.3V ought to be sufficient.
If I'm reading the SOA graph correctly, I'm well within the safe area for both.
Could I please get a second opinion on the choice of these MOSFET based on the above requirements?
Hi permal
Attached is a list of NMOSFETs that I put together for a similar application. The $ signs indicate merit.
Hi permal
Attached is a list of NMOSFETs that I put together for a similar application. The $ signs indicate merit.Oh my gosh, you're an angel
How did you find these components? Is there an easier way than reading the data sheets for each one? The search tool at, e.g. Mouser only goes so far in what parameters you can search with. ('m probably missing something obvious)
...
...Right. So what I lack is simply experience and having done this for X years to accumulate such lists.
...Right. So what I lack is simply experience and having done this for X years to accumulate such lists.Yes, that is exactly it. The whole thing seems pretty daunting at first, but it is like all fields, you soon get the hang of it. I can remember when the first opamps came out. I looked at the data sheets and thought that I would never be able to understand all that, but now I look at the same data sheets and think how basic and simple they are. And when the 7400 logic chip came out, the data sheet seemed so complicated that I gave up.
But, I think I mentioned this before, variety reduction (VR) is the big secret. There are literally millions of component types available, so what you need to do is just focus on your area of electronics, and at the moment I would guess that you would be looking for NMOFETS and PMOSFETS to suit your 3V3 logic system. So the best thing to do is just chose one NMOSFET and one PMOSFET that will do all the tasks you will require in your 3V3 system. So for example, instead of choosing MOSFETs that will handle 500mA, go for a 6A capability. There are two suitable N & P MOSFETs from the lists I posted.
Then get to know those preferred devices well. After that, when you do a new design, you do not need to search for suitable devices. Instead you design your new circuit around the devices you know. Also, this approach radically reduces the number of components you need to stock.
Attached is a list of NMOSFETs that I put together for a similar application. The $ sign indicates merit.
Attached is a list of NMOSFETs that I put together for a similar application. The $ sign indicates merit.
Love to see AO fets which I have as well because of their good performance / price ratio (but I haven't put into application yet). Question, was Rds@2.5V actually measured or inferred from the datasheet?
Attached below is a snapshot of my directory for PMOSFETs up to 10A, which you may be interested in:
So based on @Spec's list, I'm looking at Si2374DS for an N-channel version. Searching for similar chips, but P-channel, I found SI2323CDS which looks nearly identical to my untrained mind, except the mode.
* Any objections to these?
* Both datasheets specify "Continuous Drain Current" in their Abs Max section, with the caveat that t=5S. How is that "continuous"?
* As I'm going to need eight of each and they'll all be placed on a row (at the I/O connectors), I'm just wondering if another model in dual/quad package is a better option?
Attached below is a snapshot of my directory for PMOSFETs up to 10A, which you may be interested in:You should put them up on Github or some such, I'm sure other people like me also struggle with this.
Your choice is fine, but I would recommend the Si2312CD (NMOSFET), and Si2323CDS (PMOSFET) (as you chose) because they are the latest MOSFETs from Vishay.
You can get dual MOSFETs in one case, but I would advise sticking to singles. They are in an SOT23 case which is pretty compact, but bigger than most cases these days, so easier to handle.
Hmm that's an idea. The thing is that the list changes frequently as new devices become available. Also I have multiple lists for most components so where would it end.
(The NMOSFET table took 12 hours to do, so it is not a quick task.)
Your choice is fine, but I would recommend the Si2312CD (NMOSFET), and Si2323CDS (PMOSFET) (as you chose) because they are the latest MOSFETs from Vishay.
You can get dual MOSFETs in one case, but I would advise sticking to singles. They are in an SOT23 case which is pretty compact, but bigger than most cases these days, so easier to handle.Ok, I'll go with your recommendation Finally I can make some progress on this projectHmm that's an idea. The thing is that the list changes frequently as new devices become available. Also I have multiple lists for most components so where would it end.
(The NMOSFET table took 12 hours to do, so it is not a quick task.)I have no idea how you do it, but I keep all my documents, code and such in Git. It not only gives you revision history, it also acts as an extra backup. I've found this to be helpful even for schematics although they are not as easy to compare as source code, but it is doable. I've lost count of the times where I've reverted back to a previous version to start over. Perhaps commercial tools have this built in, KiCad does not.
I'm not surprised it takes a lot time to compile the list, god knows I've spent hours just trying to select these and I had good help from you.
...as close as possible, using as short leads as possible
Wow, do I feel the fool now.
Thank you for you patience, @Spec.
The circuit as I drew it is what I need - 5 and 12V output so your latest schematic will do the trick.
I suppose D2 strictly needed since I'll be controlling that only via the MCP23107 at 3.3V?.
Quote...as close as possible, using as short leads as possibleCan please you elaborate on the reason behind that?