Why this transistor?

Discussion in 'Electronic Design' started by Anthony Fremont, Apr 5, 2007.

  1. I'm looking at this schematic and am wondering why the designer chose a
    2N2369 over a 2N2222 or 2N3904? I looked at the datasheet for the 2N2369,
    and I didn't see anythng amazing about jumping off the page. Did I miss
    something. The maximum frequency expected would be under 30MHz.
    http://homepage.eircom.net/~ei9gq/stab.html

    He also makes a big deal out of the particular op-amp chosen as (what
    appears to be) a simple voltage follower. Any reason that you all can think
    of?
     
    Anthony Fremont, Apr 5, 2007
    #1
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  2. Anthony Fremont

    Andrew Holme Guest

    "Anthony Fremont" <> wrote in message
    news:...
    > I'm looking at this schematic and am wondering why the designer chose a
    > 2N2369 over a 2N2222 or 2N3904? I looked at the datasheet for the 2N2369,
    > and I didn't see anythng amazing about jumping off the page. Did I miss
    > something. The maximum frequency expected would be under 30MHz.
    > http://homepage.eircom.net/~ei9gq/stab.html
    >
    > He also makes a big deal out of the particular op-amp chosen as (what
    > appears to be) a simple voltage follower. Any reason that you all can
    > think of?


    Lots of NPN transistors, including the ones you mention, would work equally
    well there. He probably had a spare 2N2369 in his junk box.

    The op-amp needs to work from a single 5V supply, with (ideally)
    rail-to-rail input and output range - or as close as you can get to it.
     
    Andrew Holme, Apr 5, 2007
    #2
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  3. On Thu, 5 Apr 2007 08:01:14 -0500, in sci.electronics.design "Anthony
    Fremont" <> wrote:

    >I'm looking at this schematic and am wondering why the designer chose a
    >2N2369 over a 2N2222 or 2N3904? I looked at the datasheet for the 2N2369,
    >and I didn't see anythng amazing about jumping off the page. Did I miss
    >something. The maximum frequency expected would be under 30MHz.
    >http://homepage.eircom.net/~ei9gq/stab.html
    >
    >He also makes a big deal out of the particular op-amp chosen as (what
    >appears to be) a simple voltage follower. Any reason that you all can think
    >of?
    >

    I think he just has a big bag of 2N2369s
    http://homepage.eircom.net/~ei9gq/2m.html


    martin
     
    martin griffith, Apr 5, 2007
    #3
  4. Anthony Fremont

    Eeyore Guest

    Anthony Fremont wrote:

    > I'm looking at this schematic and am wondering why the designer chose a
    > 2N2369 over a 2N2222 or 2N3904?


    Because he had one already probably !

    Why did you expect to see him use a 2222 or 3904 ? Other devices do exist you
    know ! Most are quite considerably superior.

    Graham
     
    Eeyore, Apr 5, 2007
    #4
  5. Andrew Holme wrote:
    > "Anthony Fremont" <> wrote in message
    > news:...
    >> I'm looking at this schematic and am wondering why the designer
    >> chose a 2N2369 over a 2N2222 or 2N3904? I looked at the datasheet
    >> for the 2N2369, and I didn't see anythng amazing about jumping off
    >> the page. Did I miss something. The maximum frequency expected
    >> would be under 30MHz. http://homepage.eircom.net/~ei9gq/stab.html
    >>
    >> He also makes a big deal out of the particular op-amp chosen as (what
    >> appears to be) a simple voltage follower. Any reason that you all
    >> can think of?

    >
    > Lots of NPN transistors, including the ones you mention, would work
    > equally well there. He probably had a spare 2N2369 in his junk box.


    Ok then, I was just wondering if there was something special about it. It
    does specify a much faster Toff, but that is with a much lighter collector
    current (if that matters?).

    > The op-amp needs to work from a single 5V supply, with (ideally)
    > rail-to-rail input and output range - or as close as you can get to
    > it.


    OK, well that's not a big problem either. I notice he only wants a range of
    1V - 4V out of it. Thanks. :)
     
    Anthony Fremont, Apr 5, 2007
    #5
  6. Anthony Fremont, Apr 5, 2007
    #6
  7. Anthony Fremont

    Jim Thompson Guest

    On Thu, 5 Apr 2007 08:01:14 -0500, "Anthony Fremont"
    <> wrote:

    >I'm looking at this schematic and am wondering why the designer chose a
    >2N2369 over a 2N2222 or 2N3904? I looked at the datasheet for the 2N2369,
    >and I didn't see anythng amazing about jumping off the page. Did I miss
    >something. The maximum frequency expected would be under 30MHz.
    >http://homepage.eircom.net/~ei9gq/stab.html
    >
    >He also makes a big deal out of the particular op-amp chosen as (what
    >appears to be) a simple voltage follower. Any reason that you all can think
    >of?
    >


    2N2369 is GOLD-DOPED, thus fast recovery from saturation (if
    over-driven).

    ...Jim Thompson
    --
    | James E.Thompson, P.E. | mens |
    | Analog Innovations, Inc. | et |
    | Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
    | Phoenix, Arizona Voice:(480)460-2350 | |
    | E-mail Address at Website Fax:(480)460-2142 | Brass Rat |
    | http://www.analog-innovations.com | 1962 |

    America: Land of the Free, Because of the Brave
     
    Jim Thompson, Apr 5, 2007
    #7
  8. "Anthony Fremont" <> wrote in message
    news:...
    > I'm looking at this schematic and am wondering why the designer chose a
    > 2N2369 over a 2N2222 or 2N3904? I looked at the datasheet for the 2N2369,
    > and I didn't see anythng amazing about jumping off the page. Did I miss
    > something. The maximum frequency expected would be under 30MHz.
    > http://homepage.eircom.net/~ei9gq/stab.html
    >
    > He also makes a big deal out of the particular op-amp chosen as (what
    > appears to be) a simple voltage follower. Any reason that you all can
    > think of?
    >

    Try running a 2N2222 at 30MHz square wave/saturated and you see why he uses
    a 2N2369. Storage time! The alternative is a Baker Clamp.

    Don't know about the op amp. I'm sure something cheap and nasty would do the
    job.

    Graham H
     
    Graham Holloway, Apr 5, 2007
    #8
  9. Eeyore wrote:
    > Anthony Fremont wrote:
    >
    >> I'm looking at this schematic and am wondering why the designer
    >> chose a 2N2369 over a 2N2222 or 2N3904?

    >
    > Because he had one already probably !


    That seems to be the consensus.

    > Why did you expect to see him use a 2222 or 3904 ?


    Generally, when it doesn't really matter, these parts tend to be the ones
    actually specified or listed as alternates. Why do you think I'm asking?
    I'd like to know about some decent/better alternatives myself. I was hoping
    that someone that had used the 2N2369 would speak up and say "ya, ist gut"
    or something like that. ;-)

    > Other devices do
    > exist you know ! Most are quite considerably superior.


    Ok, good to know. I'll be sure to stock up on the quality part numbers you
    provided. Maybe this is why 3904's and 2222's rule?
     
    Anthony Fremont, Apr 5, 2007
    #9
  10. Jim Thompson wrote:

    >
    > 2N2369 is GOLD-DOPED, thus fast recovery from saturation (if
    > over-driven).


    Like this Eeyore.....this is the kind of thing I was hoping to see......an
    actual reason to use that part over a more common jelly-bean. I'm guessing
    this is where the Toff thingy comes in? Of course it's now a moot point
    since it's an obsolete part, but maybe the designer liked the metal cans.
     
    Anthony Fremont, Apr 5, 2007
    #10
  11. Anthony Fremont

    Jim Thompson Guest

    On Thu, 5 Apr 2007 10:08:30 -0500, "Anthony Fremont"
    <> wrote:

    >Jim Thompson wrote:
    >
    >>
    >> 2N2369 is GOLD-DOPED, thus fast recovery from saturation (if
    >> over-driven).

    >
    >Like this Eeyore.....this is the kind of thing I was hoping to see......an
    >actual reason to use that part over a more common jelly-bean. I'm guessing
    >this is where the Toff thingy comes in? Of course it's now a moot point
    >since it's an obsolete part, but maybe the designer liked the metal cans.
    >
    >


    I still have a bunch of them myself ;-)

    ...Jim Thompson
    --
    | James E.Thompson, P.E. | mens |
    | Analog Innovations, Inc. | et |
    | Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
    | Phoenix, Arizona Voice:(480)460-2350 | |
    | E-mail Address at Website Fax:(480)460-2142 | Brass Rat |
    | http://www.analog-innovations.com | 1962 |

    America: Land of the Free, Because of the Brave
     
    Jim Thompson, Apr 5, 2007
    #11
  12. Graham Holloway wrote:
    > "Anthony Fremont" <> wrote in message
    > news:...
    >> I'm looking at this schematic and am wondering why the designer
    >> chose a 2N2369 over a 2N2222 or 2N3904? I looked at the datasheet
    >> for the 2N2369, and I didn't see anythng amazing about jumping off
    >> the page. Did I miss something. The maximum frequency expected
    >> would be under 30MHz. http://homepage.eircom.net/~ei9gq/stab.html
    >>
    >> He also makes a big deal out of the particular op-amp chosen as (what
    >> appears to be) a simple voltage follower. Any reason that you all
    >> can think of?
    >>

    > Try running a 2N2222 at 30MHz square wave/saturated and you see why
    > he uses a 2N2369. Storage time! The alternative is a Baker Clamp.


    Thanks Graham. :) The fT's aren't that far seperated, so I'd ass-u-med
    similar characteristics in that area, but I'm learning differently now. ;-)

    > Don't know about the op amp. I'm sure something cheap and nasty would
    > do the job.


    Ok, he sure makes a deal over it, but doesn't explain why.
     
    Anthony Fremont, Apr 5, 2007
    #12
  13. Jim Thompson wrote:
    > On Thu, 5 Apr 2007 10:08:30 -0500, "Anthony Fremont"
    > <> wrote:
    >
    >> Jim Thompson wrote:
    >>
    >>>
    >>> 2N2369 is GOLD-DOPED, thus fast recovery from saturation (if
    >>> over-driven).

    >>
    >> Like this Eeyore.....this is the kind of thing I was hoping to
    >> see......an actual reason to use that part over a more common
    >> jelly-bean. I'm guessing this is where the Toff thingy comes in?
    >> Of course it's now a moot point since it's an obsolete part, but
    >> maybe the designer liked the metal cans.
    >>
    >>

    >
    > I still have a bunch of them myself ;-)


    Is Toff the thing I should have been looking at to determine this? Gone are
    the days of loads of charts relating everything, now I mostly see a few
    paramaters specified that (at least AFAIC) leave no way to extrapolate
    anything useful. :-?
     
    Anthony Fremont, Apr 5, 2007
    #13
  14. Anthony Fremont

    Jim Thompson Guest

    On Thu, 5 Apr 2007 10:45:35 -0500, "Anthony Fremont"
    <> wrote:

    >Jim Thompson wrote:
    >> On Thu, 5 Apr 2007 10:08:30 -0500, "Anthony Fremont"
    >> <> wrote:
    >>
    >>> Jim Thompson wrote:
    >>>
    >>>>
    >>>> 2N2369 is GOLD-DOPED, thus fast recovery from saturation (if
    >>>> over-driven).
    >>>
    >>> Like this Eeyore.....this is the kind of thing I was hoping to
    >>> see......an actual reason to use that part over a more common
    >>> jelly-bean. I'm guessing this is where the Toff thingy comes in?
    >>> Of course it's now a moot point since it's an obsolete part, but
    >>> maybe the designer liked the metal cans.
    >>>
    >>>

    >>
    >> I still have a bunch of them myself ;-)

    >
    >Is Toff the thing I should have been looking at to determine this? Gone are
    >the days of loads of charts relating everything, now I mostly see a few
    >paramaters specified that (at least AFAIC) leave no way to extrapolate
    >anything useful. :-?
    >


    Yes. Though I've only "looked" at a 2N2369 in the past 20 years ;-)

    ...Jim Thompson
    --
    | James E.Thompson, P.E. | mens |
    | Analog Innovations, Inc. | et |
    | Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
    | Phoenix, Arizona Voice:(480)460-2350 | |
    | E-mail Address at Website Fax:(480)460-2142 | Brass Rat |
    | http://www.analog-innovations.com | 1962 |

    America: Land of the Free, Because of the Brave
     
    Jim Thompson, Apr 5, 2007
    #14
  15. Anthony Fremont

    Wimpie Guest

    On 5 abr, 15:01, "Anthony Fremont" <> wrote:
    > I'm looking at this schematic and am wondering why the designer chose a
    > 2N2369 over a 2N2222 or 2N3904? I looked at the datasheet for the 2N2369,
    > and I didn't see anythng amazing about jumping off the page. Did I miss
    > something. The maximum frequency expected would be under 30MHz.http://homepage.eircom.net/~ei9gq/stab.html
    >
    > He also makes a big deal out of the particular op-amp chosen as (what
    > appears to be) a simple voltage follower. Any reason that you all can think
    > of?


    Hello Anthony,

    If I had to choose between the 2N2369 and the 2N2222 (for your
    application), I would choose the first one.

    The 2N2222 is designed for higher current operation (larger die size,
    higher capacitance). Because of higher Ft and lower reverse
    capacitance (2n2369 device), the gain of your circuit will be higher,
    so you need to pick up less signal from your local oscillator. Check
    the datasheet from Fairchild MMBT2369A (same chip in different
    package).

    At low current (for example 3 mA), the Ft of the 2N2222 device drops
    to below 200 MHz. It remains high for the 2N2369 device (they specify
    at 500MHz at 10 mA). When you overdrive (as Jim mentioned), the 2n2369
    device remains fast, so you get good pulses out of it. The 2N2222
    device will perform less (at your relative low currents).

    The 2n3904 is in-between the two.

    Regarding the opamp, I do not have the datasheet, maybe somebody knows
    whether it is equal to the OP-07.

    Best Regards,

    Wim
    PA3DJS
     
    Wimpie, Apr 5, 2007
    #15
  16. Anthony Fremont

    Joerg Guest

    Anthony Fremont wrote:
    > Jim Thompson wrote:
    >
    >>On Thu, 5 Apr 2007 10:08:30 -0500, "Anthony Fremont"
    >><> wrote:
    >>
    >>
    >>>Jim Thompson wrote:
    >>>
    >>>
    >>>>2N2369 is GOLD-DOPED, thus fast recovery from saturation (if
    >>>>over-driven).
    >>>
    >>>Like this Eeyore.....this is the kind of thing I was hoping to
    >>>see......an actual reason to use that part over a more common
    >>>jelly-bean. I'm guessing this is where the Toff thingy comes in?
    >>>Of course it's now a moot point since it's an obsolete part, but
    >>>maybe the designer liked the metal cans.
    >>>
    >>>

    >>
    >>I still have a bunch of them myself ;-)

    >
    >
    > Is Toff the thing I should have been looking at to determine this? Gone are
    > the days of loads of charts relating everything, now I mostly see a few
    > paramaters specified that (at least AFAIC) leave no way to extrapolate
    > anything useful. :-?
    >


    When using the 2369 or similar gold-doped transistors with fast
    switching times just keep in mind that their hfe is much lower than what
    you may be used to from the 3904. That's the price to pay for speed. IOW
    there is no free lunch:

    http://www.nxp.com/acrobat_download/datasheets/PMBT2369_4.pdf

    BTW the TO-92 version of this one seems to be on the way to memory lane,
    could become hardcore unobtanium soon. Unless Jim can spare some from
    his bag.

    The author might have used it in the circuit you posted because he
    needed the speed but not much in terms of current gain. Just one comment
    here: It isn't a good practice to drive a logic gate straight off the
    collector of a transistor. There should be a fast Schmitt first. If the
    input signal is smallish this counter might otherwise display next
    week's lottery numbers instead of the frequency.

    --
    Regards, Joerg

    http://www.analogconsultants.com
     
    Joerg, Apr 5, 2007
    #16
  17. Anthony Fremont

    Lionel Guest

    On Thu, 5 Apr 2007 14:27:30 +0100, "Andrew Holme" <>
    wrote:

    >
    >"Anthony Fremont" <> wrote in message
    >news:...
    >> I'm looking at this schematic and am wondering why the designer chose a
    >> 2N2369 over a 2N2222 or 2N3904? I looked at the datasheet for the 2N2369,
    >> and I didn't see anythng amazing about jumping off the page. Did I miss
    >> something. The maximum frequency expected would be under 30MHz.
    >> http://homepage.eircom.net/~ei9gq/stab.html
    >>
    >> He also makes a big deal out of the particular op-amp chosen as (what
    >> appears to be) a simple voltage follower. Any reason that you all can
    >> think of?

    >
    >Lots of NPN transistors, including the ones you mention, would work equally
    >well there. He probably had a spare 2N2369 in his junk box.


    That'd be my guess too. Most of us design with whatever we're
    comfortable with, & have in the parts drawers. In my case, I use a lot
    of BC5xx transistors because they're what I grew up up with, & I can
    buy them in bulk locally at dirt cheap prices.

    When you're working from a circuit like that one, as long as you've
    checked the spec's of the original part, there's no harm in
    substituting something equivalent that you already have in stock.

    --
    W "Some people are alive only because it is illegal to kill them."
    . | ,. w ,
    \|/ \|/ Perna condita delenda est
    ---^----^---------------------------------------------------------------
     
    Lionel, Apr 6, 2007
    #17
  18. Anthony Fremont

    Lionel Guest

    On Thu, 5 Apr 2007 10:00:28 -0500, "Anthony Fremont"
    <> wrote:

    >Eeyore wrote:
    >> Anthony Fremont wrote:
    >>
    >>> I'm looking at this schematic and am wondering why the designer
    >>> chose a 2N2369 over a 2N2222 or 2N3904?

    >>
    >> Because he had one already probably !

    >
    >That seems to be the consensus.
    >
    >> Why did you expect to see him use a 2222 or 3904 ?

    >
    >Generally, when it doesn't really matter, these parts tend to be the ones
    >actually specified or listed as alternates. Why do you think I'm asking?
    >I'd like to know about some decent/better alternatives myself. I was hoping
    >that someone that had used the 2N2369 would speak up and say "ya, ist gut"
    >or something like that. ;-)
    >
    >> Other devices do
    >> exist you know ! Most are quite considerably superior.

    >
    >Ok, good to know. I'll be sure to stock up on the quality part numbers you
    >provided. Maybe this is why 3904's and 2222's rule?


    Yep. They're ubiquitous in American designs. Yurrupeen designs tend to
    have lots of BC548s & BC549s for the same reasons.

    --
    W "Some people are alive only because it is illegal to kill them."
    . | ,. w ,
    \|/ \|/ Perna condita delenda est
    ---^----^---------------------------------------------------------------
     
    Lionel, Apr 6, 2007
    #18
  19. Anthony Fremont

    Eeyore Guest

    Anthony Fremont wrote:

    > Eeyore wrote:
    > > Anthony Fremont wrote:
    > >
    > >> I'm looking at this schematic and am wondering why the designer
    > >> chose a 2N2369 over a 2N2222 or 2N3904?

    > >
    > > Because he had one already probably !

    >
    > That seems to be the consensus.
    >
    > > Why did you expect to see him use a 2222 or 3904 ?

    >
    > Generally, when it doesn't really matter, these parts tend to be the ones
    > actually specified or listed as alternates.


    Not in my world. They're the very last parts I'd suggest.

    2N2222s are needlessly expensive simply because they have a metal can.


    > Why do you think I'm asking?
    > I'd like to know about some decent/better alternatives myself. I was hoping
    > that someone that had used the 2N2369 would speak up and say "ya, ist gut"
    > or something like that. ;-)
    >
    > > Other devices do
    > > exist you know ! Most are quite considerably superior.

    >
    > Ok, good to know. I'll be sure to stock up on the quality part numbers you
    > provided. Maybe this is why 3904's and 2222's rule?


    They don't rule in any way shape or form.

    For general purpose medium voltage small-signal npn I'd use BC214 in the past
    and BC549 today.

    There are literally hundreds of transistors that would substitute perfectly for
    these parts.

    Graham
     
    Eeyore, Apr 6, 2007
    #19
  20. Anthony Fremont

    Eeyore Guest

    Anthony Fremont wrote:

    > Jim Thompson wrote:
    >
    > >
    > > 2N2369 is GOLD-DOPED, thus fast recovery from saturation (if
    > > over-driven).

    >
    > Like this Eeyore.....this is the kind of thing I was hoping to see......an
    > actual reason to use that part over a more common jelly-bean.


    Yet quite irrelevant to this application most likely. The signal source isn't
    shown.

    Graham
     
    Eeyore, Apr 6, 2007
    #20
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