2N7000... any better substitue?

Discussion in 'General Electronics Chat' started by Robin66, Mar 31, 2016.

  1. Robin66

    Thread Starter Member

    Jan 5, 2016
    102
    3
    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?
     
  2. dannyf

    Well-Known Member

    Sep 13, 2015
    1,824
    364
    I would think the suggestion is application specific.
     
  3. Robin66

    Thread Starter Member

    Jan 5, 2016
    102
    3
    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.
     
  4. dannyf

    Well-Known Member

    Sep 13, 2015
    1,824
    364
    "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.
     
  5. Robin66

    Thread Starter Member

    Jan 5, 2016
    102
    3
    Agreed. I take it then that you don't know of any device somewhere between the 2N7000 and the theoretical ideal FET?
     
  6. dannyf

    Well-Known Member

    Sep 13, 2015
    1,824
    364
    The answer is obviously "countless".
     
  7. Robin66

    Thread Starter Member

    Jan 5, 2016
    102
    3
    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.
     
  8. dannyf

    Well-Known Member

    Sep 13, 2015
    1,824
    364
    Do a parametric search and you will get a bunch.
     
  9. Robin66

    Thread Starter Member

    Jan 5, 2016
    102
    3
    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.
     
  10. GopherT

    AAC Fanatic!

    Nov 23, 2012
    6,061
    3,823
    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: Mar 31, 2016
    absf and kubeek like this.
  11. kubeek

    AAC Fanatic!

    Sep 20, 2005
    4,670
    804
    Try looking at fets in to-223, so8 or even sot-23, depending on what power dissipation you expect.
     
  12. ErnieM

    AAC Fanatic!

    Apr 24, 2011
    7,392
    1,606
    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.
     
  13. Robin66

    Thread Starter Member

    Jan 5, 2016
    102
    3
    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?
     
  14. GopherT

    AAC Fanatic!

    Nov 23, 2012
    6,061
    3,823
    If a 2N7000 works in the prototype, a better MOSFet will work on the PCB.
     
    Robin66 likes this.
  15. ErnieM

    AAC Fanatic!

    Apr 24, 2011
    7,392
    1,606
    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.
     
    Robin66 and GopherT like this.
  16. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
    5,699
    905
    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
     
    Robin66 likes this.
  17. Robin66

    Thread Starter Member

    Jan 5, 2016
    102
    3
    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.
     
  18. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
    4,771
    971
    Just a FYI..
    This place has TONS of SMT to TH adapters,etc..
    fast shipping/low cost,etc..
    Quite a few can be found on ebay too for even cheaper but I've used these guys in the past and been happy with them..
    http://www.proto-advantage.com/store/
     
  19. GopherT

    AAC Fanatic!

    Nov 23, 2012
    6,061
    3,823
  20. Lestraveled

    Well-Known Member

    May 19, 2014
    1,957
    1,215
    You can take a surface mount part and super glue it upside down on your perf board. Just remember to mark pin one.
     
Loading...