Looking for a mosfet recommendation (SOLVED)
Hi all. I need my P1 to switch a load on and off, and I thought I'd try using a mosfet for a change. So I don't know from mosfets, but I'm using this as my guide (from learningaboutelectronics.com/Articles/N-channel-MOSFET-switch-circuit.php):
![N-channel-MOSFET-switch-circuit.png](http://www.learningaboutelectronics.com/images/N-channel-MOSFET-switch-circuit.png)
I figure I can replace the 3V gate input with a Prop pin and replace the 6V buzzer with my 5V device. Does that sound reasonable so far?
Now the aforementioned web page recommends the 2N7000 mosfet, which IIRTDC has a maximum drain current of 200mA. Unfortunately, the circuit I want to control draws ~250mA, so the 2N7000 is out. The related NDS7002A could work, but I'm only finding surface mount packages.
I'm hoping someone can help me find something like a 2N7000 in a TO-92 that can switch maybe 300mA to be on the safe side.
![N-channel-MOSFET-switch-circuit.png](http://www.learningaboutelectronics.com/images/N-channel-MOSFET-switch-circuit.png)
I figure I can replace the 3V gate input with a Prop pin and replace the 6V buzzer with my 5V device. Does that sound reasonable so far?
Now the aforementioned web page recommends the 2N7000 mosfet, which IIRTDC has a maximum drain current of 200mA. Unfortunately, the circuit I want to control draws ~250mA, so the 2N7000 is out. The related NDS7002A could work, but I'm only finding surface mount packages.
I'm hoping someone can help me find something like a 2N7000 in a TO-92 that can switch maybe 300mA to be on the safe side.
Comments
Here's a schematic:
Incidently, I don't recommend going this route, unless those are the only parts you have on hand. It would be much better to use a gate driver like the MIC4427-series. But if the load is very light, you could get by with just a ZVN4424A MOSFET without a gate driver.
BTW, be sure to connect the drive voltage negative supply to ground right at the MOSFET pin. You do not want load current flowing through any logic ground wires or traces!
-Phil
-Phil
P.S. I know the thread title is " looking for a mosfet" but the application is driving a 250ma low voltage buzzer. If I saw a gate-driver + MOSFET in a pcb driving a little old buzzer, I'd laugh.
There are only hundreds of npn bjts in to92 that you can choose from these days, rather than thousands, however the 2N5550 is cheap and handles 600ma at <100mv Vce(sat). I just remembered that I used to use BC337s for this kind of thing back in the day (even when I used mosfets for other things), they handle 800ma and were a good all-round npn.
TO-92 is very much trialing edge, but if you go to Digikey and search for through-hole with VGS <= 2V, you find the cheapest is NTD3055L104-1G in IPAK
If you look for easy to use SMD packages, the BUK98150-55A/CUF in SOT223 is cheaper than any thru-hold alternative,
Older parts tended to not target explicit specified 3v3 operation, and FDT439N on SOT223 is well spec'd (RDS(on) = 0.058 Ω @ VGS = 2.5 V) but not so easy to find.
It may be that packages like SO-8 are more a middle-ground, of easy to solder but modern enough to have 3V drive spec's - here, you may find dual-mosfets are more mainstream.
eg The DMN2028USS in SO-8 has 2.5V drive spec and includes ESD diodes. FDS9926A & NTMD6N02 are dual fets in SO-8
So thank you all for assuming I would understand your replies!
NUD3124LT1G
I used it to drive some 120 volt 10 amp relays and It took the place of 5 parts.
-Phil
I keep saying that an npn is far simpler, even if you do need one resistor.
If the buzzer happens to be electromechanical (peobably not?), it will kick out nasty high voltage spikes.
Diodes Inc has some nice Thru-hole mosfets with low thresholds, like good for 3V gate drive, but I don’t know about TO92 size. (DMT6009). Mosfets may seem simpler at first glance, but there are pitfalls for the unwary, complications.
+1 for the Zetex - I use these for those special cases for these very reasons. DIODES are now manufacturing ZETEX.
As for "simpler" I agree, but I'd use the digital transistors in SOT-23 packs that have series resistors built-in. One tiny black dot on the board is all I need to handle 1A or more.
TO-92 case, 600mA max, hFE 100 min at 150mA
30c at Mouser
As I'm learning in this thread
Btw, I'm not using a buzzer. That's just an example diagram I found on the interwebs.
-Phil
However it doesn't matter much because at 5V or 6V you are not going to be switching any high power load. If however you are thinking of connecting inductive loads to the 5V rail then you will have to protect your whole board from inductive spikes which may also be radiated, but that depends upon the load.
Is it a national security matter? Your call.
Basically, I tried to communicate something and failed, and now I'm doing a little post mortem to see where my judgment was off.
It would be useful if you could provide some details about the device you want to drive, such as it's resistance, inductance or capacitance. An RLC model of the device would be useful.
No you've told us it's not a buzzer a number of posts ago. It really matters but you're not telling us. Do you want help???
1. Is it an inductive load?
-Phil
In my first post I simply referred to switching "light loads" with a cheap and effective npn since that is the design choice I make for anything like this, especially in to-92 which aren't amenable to the larger die area of mosfets. Basically, the lower the rds(on), the more parallel elements in the mosfet array, the larger the die but to-92 is limited.
However when I read the thread later on there were posts talking about gate drivers so prompting for more specific information I ask the question "What's all this about? Isn't it just a buzzer?" but got no confirmation or correction. Nonetheless, I wasn't too fussed about the load because what can you be switching other than a light load at 250ma at 5V?
So all the while if you read the posts you could say "hang on, hang on guys, I'm just trying to switch power to another xyz circuit board, not PWM a motor" or something like that.
All this because you toyed with the foolish idea of using a mosfet instead of a bjt to save one resistor
BTW - you still haven't told us what "the device" is.
If I ask Google for directions to some place, it normally assumes I am driving and might direct me out of the way onto a freeway or something. But I may be cycling and so I let Google know that too so that it gives me the correct answer. Nonetheless, I decide to take a shortcut through the bush instead.
A SOT-23 sized SMD package can deliver down to VDS - 12V 10.7A (Ta) 1.2V, 4.5V Rds = 10mOhm @ 9.7A, 4.5V Vgs(th) = 800mV @ 250µA
In BJT tech, the device would be something like BC337-40 - that's TO-92, and has good HFE so does not need very low base resistors when used with a ~300mA load.