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small 400V pnp sot-23 transistor, xxxTA94, etc.

Discussion in 'Electronic Design' started by Winfield Hill, Oct 12, 2006.

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  1. The A92 or mpsa92 is a popular 300V pnp transistor in a
    TO-92 package, with a number of sot-23 SMD versions also
    manufactured, most commonly the mmbta92. Most of these
    300V transistors have breakdown voltages of 400 to 450V,
    in my experience, and on occaision I've used them in
    designs right up to 300V. But I didn't realize until
    recently that there was an official 400V version, the
    mpsa94, with a number of sot-23 offerings: e.g., the
    mmbta94, cmpta94, hmbta94 and fhta94.

    However, a quick look failed to turn up any distributor
    carrying any of these parts. Does anyone here have any
    experience with these, or know of other 400V sot-23 pnp
    transistors that might be readily available?
     
  2. Winfield Hill wrote...
    Ah, I found the Zetex FMMT558 and FMMT560 sot-23 parts,
    with 400 and 500V ratings. How'd I miss those? Hmm,
    Fairchild offers their FMMT560 rated at 60V -- oops!
     
  3. Digikey shows >1K in stock of both Panasonic 2SB14880PA and Zetex
    FMMT558TA both in full and broken reels. A bit pricey, though (
    0.282/2K and 0.1728/3K vs. 0.06/3K for the jellybean MMBTA92).



    Best regards,
    Spehro Pefhany
     
  4. Spehro Pefhany wrote...
    The Panasonic isn't a sot-23, but the Zetex fmmt558 is an
    ideal replacement for the A92. According to the datasheet
    it has less capacitance, a higher fT, and better gain over
    a wider current range. What's not to like? Later today
    I'll make the change in my 2.2kV amplifier and find out.
    Sometimes money is no object. That's easy to say when
    only 11 cents is involved. :) Well, actually, with 16
    per board it's $1.76, but that's on a large PCB with 600
    parts and a $400 per board cost in a run of 40 boards.
     
  5. Oops. Not even SMT, but at least a pleasant ~0.1" pitch through-hole
    package with good power dissipation. ;-)
    Sounds like an interesting circuit.
    I didn't think it would matter much to you, but it's interesting that
    there's a 280% price increase for a 25% improvement in Vceo.


    Best regards,
    Spehro Pefhany
     
  6. Fred Bartoli

    Fred Bartoli Guest

    Spehro Pefhany a écrit :
    But the Zetex part is a 825% increase in Vceo over the Fairchild's one,
    for 0% increase in part#.

    Let see the scene:
    Design some nice 400V gadget...
    Prototype, blah...
    Run into prod.
    First runs OK.
    Purchase dep.: Oh, but why would we pay Zetex that much. Fairchild has
    the same one. No pb.

    Prod: Build new boards...
    Board: Kaboum!
    Board: Kaboum!
    Board: Kaboum!
    Board: Kaboum!

    Designer: what part did you get mounted?
    Prod: FMMT560
    Board: still Kaboum!
    Designer: wait! That's not possible.
    Prod: Yes, but the board doesn't say so: Kaboum!
    Designer: Are you sure it's FMMT560?
    Purchase: Sure! Look at the delivery note.
    Designer: scratch...
    Board: Kaboum!

    2 weeks later:
    Customer: Hey, where are my boards?
    Board: Kaboum!
    Sales dep.: Oh, your order must have got lost by the postal service. We
    never received it. We'll send you all our stock tomorrow.
    Boss: What's the f..k, designer? You're fired.
    Designer: but...
    Board: Kaboum!
    ....
    ....
    Tech: Idea!...FMMT560->MMBT560... Eureka!
    Tech: Look! That FMMT560 is a 60V part!
    Purchase dep.: Those designers are really nothing but morons.
    Prod: Hmmm, but the first board runs worked OK.
    Boss: You know, components have some tolerances. First ones must have
    been very good.
    Prod: Amen.
    Purchase dep. : Amen.
    QA dep.: Amen.
    QA dep.: Ouch, but that's a huge Vceo variation. Those FMMT560 are
    really crap. Mark them as forbidden, or don't use them with more than 6V
    VCE.
    ....

    Zetex: Why don't we sell our nice transistors anymore?

    ....
    ....

    Win: Too bad... Zetex has just dropped that wonderful FMMT560 I was fond of.
     
  7. Fred Bartoli wrote...
    LOL, nice story. Yes, I saw the amazing FUBAR with the Zetex
    and Fairchild FMMT560 a few days ago; it raised my eyebrows!
     
  8. Joerg

    Joerg Guest

    Hello Winfield,
    If it wouldn't take more than a usec to turn off I'd really like it as well.

    If you'd buy 10k of them you could get them for 12c ;-)
     
  9. Joerg wrote...
    I'm sure both the fmmt558 and the A92 can turn off in well
    under a usec, if it's current sinking or steering you're
    thinking of. But do you mean the output has to slew 400V
    in under 1us, or > 4x10^8V/s? Assuming an external node
    capacitance of 5pF plus an estimated 3pF for the transistor
    over most of the excursion, the load current would have to
    be i >= C dV/dt = 3.2mA. Since that's quite reasonable,
    it would seem these transistors may meet your requirement.
    Indeed. It's the nature of high-voltage series-cascode
    applications to use a lot of transistors per circuit. For
    example, in my circuit I used four for each amplifier, but
    I should have used five. If I had added the rail-current
    monitoring circuit I envisioned, it would have been 15 per
    amplifier. If I had then beefed up the HV amplifier to a
    full push-pull configuration, to improve speed, it could
    have meant 35 of the A92 or A42 transistors per amplifier
    (thanks for machine assembly). And if I had then increased
    the voltage range to beyond 2.5kV, it would have been...
     
  10. Joerg

    Joerg Guest

    Hello Win,
    I was thinking about usage in a boost or SEPIC converter. A microsecond
    can be quite painful when the whole conduction phase is 5usec or so.
    There are some FETs but the smaller ones in SOT23 or SOT223 are mostly
    from EU companies and they can be an absolute pain to deal with from
    over here. May last attempt at that was with the BSP297 and after two
    hours on the phone I vowed to never do that again. Being fluent in
    German did not help one bit, they simply couldn't get them to us. Or
    maybe sales volume didn't matter...
    That's the beauty of today's jelly-bean parts. People say that our youth
    doesn't have the available resources to build electronics projects.
    That's nonsense. Sure we had a radio store in the next town (one hour by
    bicycle) but one of those transistors would have cost a fortune. There
    was no Digikey.
     
  11. Well, in some ways it is better; in others worse. I used to be able
    to just go to any of several local stores and persuse through table
    after table of parts and components in a warehouse kind of place; or
    go through Radio Shack (even before Tandy bought them) and see most of
    the entire store with parts; and so on. I seem to recall at least two
    or three RS stores in the city area (good part sources), an Allied
    Radio electronics warehouse store with a huge resource I could go
    through by hand; a United Radio store with parts everywhere; and two
    other "surplus" electronics stores I would frequent.

    ALL (every single one) of these are essentially gone. The RS stores
    are no longer a resource to speak of, even though there are more of
    them now. There is a Norvac Electronics store here. And it has parts
    -- but high priced "replacement brand" (read: NTE) parts for the
    larger part of it. Some interesting things once in a while.

    This, in a city metro area with now 1.5 million people.

    Of course, there are really great new options, too. I would never
    have been able to afford quality boards made for 1, 2, or 4 off kinds
    of things. My selection of parts are fantastic, and so on. So many
    more things are sincerely possible to consider realistically doing
    than there is time for, as a hobbyist with family pressures and a
    profoundly autistic child can manage.

    However, I'm finding that transistors the size of salt grains without
    the possibility of any markings (unless they placed the letters on
    them pixel-atom by pixel-atom), the need for more expensive soldering
    tools and magnifiers (as I age), and the relative higher difficulties
    of actually finding and using parts I can put on a protoboard meaning
    that I really need those board houses more.

    Some of it, though, at least for young kids, is that access to those
    who know a little about electronics (and I'm not talking about
    experts, just folks with some "playing around" experience who are
    there when a kid has a simple question coming to mind) seems to be in
    a diminishing ratio. There are more folks in the business, but fewer
    neighbors to ask, it seems. Certainly, when I was growing up there
    were many with at least some military experience in electronics you'd
    meet and others, too. I used to also have several neighbors in an
    easy 4-5 mile bicycle riding radius of me working on building their
    own telescopes. Also, into rocketry. And so on. I can't say I know
    where any of that is going on within many more miles of here, now. If
    at all. (I've lived in the same community my entire life.)

    On the other hand, there is the internet, too. So that's to the good
    side of this.

    Both parents working, or one working two jobs, the intrusion of TV and
    gaming systems into our time, the hours applied per individual adult
    and child for hobby learning has diminished, I suspect. People don't
    build their own barns, replace their own rooftops, repair their own
    plumbing or lines coming into the house, etc. They hire it, if they
    can. A transition from broad to specialized knowledge, a dependance
    upon a surrounding supports in society, etc.

    I used to know lots and lots of neighbors by the hobbies they were
    into, in fact. "Oh. That's Joe. He's really into model planes a
    lot." That kind of thing. Now, often when I ask a parent or adult I
    know, "What kind of hobbies do you like to do?" I get a blank stare,
    much more often than I ever used to.

    Jon
     
  12. Joerg

    Joerg Guest

    Hello Jon,
    Our RS has shut down a few years ago. Because a, gasp, cell phone store :-(

    Same here. My last designs contain lots of 0402. Very tough, even with
    #3 glasses plus magnifier.


    Well, they should learn using usenet :)))

    Ham radio club meetings are a good opportunity to find those who still
    build stuff from scratch. That's how I found mentors when I was a kid
    because there was nobody else to ask in our neighborhood. Having a ham
    radio license helps even more. You can go onto the local 2m channel and
    ask. Chances are that someone will respond "Oh, that's a tough one but
    I've got a Tek scope. Come on over and we'll figure it out.".

    No with me. I've laid lots of tile, re-did a bathroom, then another,
    then another. Many times hiring out results in huge costs. A neighbor
    was just quoted a whopping $33k (!) just to replace a deck.

    Ok, we did hire out the re-roofing but we needed a rather complicated
    metal roof. Plus my back isn't that good and it gave out when I helped
    on a re-roof project for church outreach. We were so close to the ridge
    that I pushed myself too far, happens easily when roofing. Couldn't get
    up the next morning.

    Sad, most people just hang out in front of the TV. That's their "hobby".
    In our neighborhood it's a lot better. People build cars, several
    airplanes, huge sea-going sailboats etc. There isn't one weekend where
    you don't hear some drills or sanders going.
     
  13. On Sat, 14 Oct 2006 17:43:28 GMT,
    The youth certainly has resources, more than ever before, but no
    incentive. When I was 15 I built my own stereo amp and loudspeakers
    because I wanted to have one, and commercial stuff was a lot more
    expensive. Now a kid can buy a $10 PC speaker set that sounds about as
    good as my amp back then.

    A must-have must-build category of stuff were things that blink and
    generate noise. Nowadays we have computers and other cheap gadgets that
    do more noisy blinking than we can stand.

    Another driving force behind hobby electronics was wireless
    communication. I vividly remember my first home-built matchbox-sized FM
    transmitter. What delight! The fact that operating it was kind of
    illegal was icing on the cake. Now every kid has a damn cell phone with
    which it can call every other kid in the industrialized part of the
    globe within seconds.

    Where's the fun in doung stuff yourself if you can just buy it better
    and cheaper? I mean, it's still fun, but the main driving force for kids
    is gone.

    The first computer games we played we had to invent and code ourselves
    because there were no games, at least not on the three $10000 computers
    my school had in 1985.

    Of course nowadays 2-year-olds have those ultra-cool wooden bicycles
    which hadn't yet been invented back then.

    robert
     
  14. Joerg

    Joerg Guest

    Hello Robert,

    I must say that I still do not have enough spare time to build all the
    stuff that we could use around here. Not even the stuff on the honey-do
    list: A decent level meter for X10, a non-mechanical pool timer that
    doesn't cost $500, low power AM transmitter to get web radio to other
    radios, X10 receivers that really work, and so on.


    Shhhht... :)

    Oh, there would be. If I were a kid today I'd still do what I had done
    back in school. Build the biggest honking amp that a 15 amp circuit
    could sustain. Except this time it would be class-D for even more oomph.
    Instead of scavenging tubes and TO3 transistors I'd be prying FETs out
    of discarded computer power supplies.

    They often just have to many toys, don't have to be creative anymore.
    When I grew up my favorite place was grandpa's shop.
     
  15. Eeyore

    Eeyore Guest

    Life's too easy these days.

    We also used to have to fix our own cars for example !

    Graham
     
  16. Joerg

    Joerg Guest

    Hello Graham,
    I still change the oil myself. That way the plug doesn't get
    over-torqued by some kid and I let the oil drain out overnight. Down to
    the last drop. So, the new oil stays clear for a much longer time. Also,
    I can be sure that only the good stuff is put in :)
     
  17. I still do. At least, those things that I can put my hands on. I
    pull my own axles to replace bearings, etc. Just can't trust many
    others to do the job right, anymore.

    Jon
     
  18. Eeyore

    Eeyore Guest

    I do basic routine stuff but I don't have off-road parking so it's a bit limited
    compared to earlier days when I even rebuilt engines.

    Graham
     
  19. Joerg

    Joerg Guest

    Hello Graham,
    During my university days we took a busted transmission out of an Opel
    (Vauxhall) on the German side of the border, hand carried it across the
    border to my apartment in the Netherlands, through the entrance of a
    pub, up three stories via staircase, repaired it, hand carried it back
    to Germany and put it in. All with the car parked in the road (but onto
    the curb so I could fit underneath).
     
  20. Jim Thompson

    Jim Thompson Guest

    Probably been 30 years since I last changed my own oil ;-)

    ...Jim Thompson
     
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