2N7000... any better substitue?

Thread Starter

Robin66

Joined Jan 5, 2016
266
I've read in a couple of places people being disparaging about 2N7000s, but then the suggested alternative is along the lines of AO3418 which is nothing like it: The gate charge is at least 100x greater and it's not available in a TO-92 package.

Does anyone know of a more modern version of 2N7000 but with improved Id for lower Vgs with pC gate charge (not nC)? I'm working on a Li-ion charger that drives FETs from 5V logic and I'm hoping to drive up to 1A pulsed (500mA would do) with Rds <1ohm. I'd also like to avoid spending £1 per device, although obviously I don't expect all of this quite as cheap as the 2N7000. I've tried the digikey tool to no avail.

Perhaps I'm asking for too much and 2N7000 has been criticised unfairly?
 

Thread Starter

Robin66

Joined Jan 5, 2016
266
Yes in that instance the user didn't require pC gate charge. It was fairly low speed switching. However the 2N7000 was more generally criticised as being archaic and not up to the standards of modern FET technology. But I can't find any improvement on 2N7000 that's resulted from this tech. Swapping low gate-charge for high Id is a compromise, not an outright improvement.
 

dannyf

Joined Sep 13, 2015
2,197
"the 2N7000 was more generally criticised as being archaic and not up to the standards of modern FET technology."

Unless those people can articulate why 2n7000 is no good for a particular application, such critism is non sensical and should be discarded.
 

Thread Starter

Robin66

Joined Jan 5, 2016
266
Agreed. I take it then that you don't know of any device somewhere between the 2N7000 and the theoretical ideal FET?
 

Thread Starter

Robin66

Joined Jan 5, 2016
266
Name one (in a TO92 package hopefully). I will then look at the various params I mentioned and hopefully find that they're all within the range 2N7000-->ideal.
 

Thread Starter

Robin66

Joined Jan 5, 2016
266
I've been there (digikey per my OP). No luck. I'm either going to end up compromising on package or beefing up the gate driver.
 

GopherT

Joined Nov 23, 2012
8,012
I've been there (digikey per my OP). No luck. I'm either going to end up compromising on package or beefing up the gate driver.
Then the answer is, no.

The TO-92 is not the package of future mosfet developments so, "modern" and TO-92 are not a likely pair of requirements that will get you a satisfactory answer.
 
Last edited:

ErnieM

Joined Apr 24, 2011
8,053
You want the advantages of a modern device but want that in an archaic package?

Hint: it is 2016. Try picking a package style designed in the current century and see if your choices improve.
 

Thread Starter

Robin66

Joined Jan 5, 2016
266
How do you guys breadboard with these SMD choices? Or do you go straight from paper & pen/software sim. straight to etching your pcbs? Or perhaps you solder little legs onto the SMDs?
 

GopherT

Joined Nov 23, 2012
8,012
How do you guys breadboard with these SMD choices? Or do you go straight from paper & pen/software sim. straight to etching your pcbs? Or perhaps you solder little legs onto the SMDs?
If a 2N7000 works in the prototype, a better MOSFet will work on the PCB.
 

ErnieM

Joined Apr 24, 2011
8,053
First I never use solderless breadboards. I do use FR4 boards with a sea of plated thru holes on 0.1" centers.

With these donuts everywhere many SMD parts can be soldered right to the pads, items like 0805 resistors and caps fit between any two holes nicely. SOT transistors go right down too if you put them at 45 degrees.

For other devices you can get adaptor boards to wiggle tight pins (like SOIC on 025 centers) into 0.1" holes. But for most discretes you can get them into the standard pads directly.
 

jpanhalt

Joined Jan 18, 2008
10,105
How do you guys breadboard with these SMD choices? Or do you go straight from paper & pen/software sim. straight to etching your pcbs? Or perhaps you solder little legs onto the SMDs?
If you want to use a breadboard, put an SMD onto a breakout board with normal 0.1" pin headers. Sparkfun and several other vendors have them. Here is a search for the Sparkfun boards. The SOT23 to DIP is on the second page.
https://www.sparkfun.com/categories/20

Youcan also find them on eBay probably cheaper.
John
 

Thread Starter

Robin66

Joined Jan 5, 2016
266
Ok thx for the feedback guys. It seems that I'm stuck in the past looking for a TO92 package, and of course GopherT's point about prototyping with an inferior product is true. I recently started using LTSpice and expect that I can nail down the majority of design issues in software allowing me to jump straight to etching boards for SMDs. Most of my effort after that stage will be in programming the PICs.
 
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