whats the mosfet equivalent of a 2N2222

[Thunderchild]

Well when you need a general purpose BJT you just grab a 2N2222 from your "box", but now we move to fets/mosfets what is the equivalent ? easy to get and a good all round part. I'm after a 4 V full turn on gate voltage and a couple of hundred mA capacity in TO92 type case

 

[audioguru]

The only little Mosfet in a TO-92 case that I know about is a 2N7000. Its max continuous current is 200mA and its gate-source voltage must be 10V for it to be fully turned on. With a 4.5V gate-source voltage it passes 75mA with a max voltage drop of 0.4V.

 

[Thunderchild]

hm not realy suitable, I'm considering surface mount too now as it seems all new stuff is going that way

 

[MikeMl]

... I'm considering surface mount too now as it seems all new stuff is going that way

Fairchild has hundreds of small surface-mount NFets that meet your requirements.

 

[Thunderchild]

well i looked at what farnell have under "digital mosfets" and yea lots of fair xchild came up but the min threshold could be 0.65-0.85 volts, yea that's a fat lot of use, what is the "0" output voltage of a PIC ? probably somewhere around that, thats not what i call a digital mosfet, I have IRF540's that are way overkill but have just the right threshold at 4V

 

[audioguru]

Don't look at the "threshold" voltage of a Mosfet because that is the gate-source voltage that barely turns on the Mosfet (or almost turns it off) so its current is only 0.25mA. Instead look at the minimum gate-source voltage that makes it have a low on-resistance so it conducts as much current that you want. A voltage of 0V turns it off.

A PIC is Cmos. So its minimum output voltage is 0.0V when it drives nothing or only drives the gate of a Mosfet. A PIC will turn off any n-channel enhancement-mode Mosfet.

 

[Thunderchild]

Well i checked the 12F615 datasheet which is my bog standard dip8 pic and they will only guarantee a low output voltage of nomore than 0.6V, This design has to sit in standby for long periods of time, a 0.25mA leak on two mosfets may not be an option, I think I may stick with the 2N2222 BJT's

The IRF540 Mentioned earlier has a minimum turn on voltage of 2V so looking much better but is rather bulky to turn on a relay with a 60mA coil current

 

[bountyhunter]

the min threshold could be 0.65-0.85 volts,

Then you don't want a FET, you want a bipolar.

 

[bountyhunter]

You need to spec ID, VGS and max working voltage.

 

[Thunderchild]

yea, having introduce a "huge" relay to the design that requires an "on" pulse and an "off" pulse I thought I'd cut down the parts as much as possible and use a mosfet to get rid of the base resistor, obviously not a good idea, I'll stick with BJT's

 

[audioguru]

Well i checked the 12F615 datasheet which is my bog standard dip8 pic and they will only guarantee a low output voltage of nomore than 0.6V

Correct, when the PIC output is sinking 8.5mA.
But when a PIC output drives only the gate of an N-channel Mosfet then the current is zero so its output low voltage is zero.

This design has to sit in standby for long periods of time, a 0.25mA leak on two mosfets may not be an option

With the gate voltage of 0V from the PIC then the Mosfets will be completely turned off with no leakage current.

The IRF540 Mentioned earlier has a minimum turn on voltage of 2V so looking much better but is rather bulky to turn on a relay with a 60mA coil current.

Some IRF540 Mosfets need a gate-source voltage of 2V and some need 4V to conduct only 0.25mA. It is spec'd to turn on properly only when its gate-source voltage is 10V.
There are many "logic-level" mosfets that are spec'd to turn on properly when their gate-source voltage is 4.5V or more.

 

[Thunderchild]

oh right did not realize that about the IRF540, looks like for the P channel counter part IRF9540 I'm using i will be ramping the gate voltage up a bit (well down to be accurate), luckily using the full 12 V of the power supply as it is buffered from the pic by a 2N2222 I can do that

 

[Brevor]

Check out the vn2222

 

[Thunderchild]

Check out the vn2222

pretty good much like the 2N7000 but with higher current capabilities, is it meant more for switch applications ?

 

[Brevor]

is it meant more for switch applications ?

Im not sure I have never actually used it, I always use 2N7000.

 

[Thunderchild]

well I've ordered some 2n7000's, what about a similar P channel part that can be found in TO-92 package ?

 

[Jony130]

BS170 is N channel
https://www.electro-tech-online.com/custompdfs/2010/07/bs170.pdf
BS208 is P channel
BS208 Datasheet pdf - P-channel enhancement mode vertical D-MOS transistor - Philips
or BS250
https://www.electro-tech-online.com/custompdfs/2010/07/bs250p.pdf
BSS92
**broken link removed**
BSS84 but no T092 version
http://www.iele.polsl.pl/elenota/Fairchild/bss84.pdf