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Transistor selection (ii)

Discussion in 'Electronic Design' started by Tim Williams, Sep 2, 2007.

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  1. Tim Williams

    Tim Williams Guest

    So for example, say I wanted a transistor:
    Vcbo >=200V
    Ic 0.1-2
    Pc >= 10W
    fT >= 100MHz
    How would I go about that?

    *Wading* through Digikey's stock, I found a 2SC5993 that's almost there
    (180V). Onsemi has a nice parametric search, but nothing in the range. I
    tried going to Fairchild's website, but their search sucks (and the whole
    website isp barely in English anyway). I've had better luck skimming over
    Japanese transistor tables! Too bad anything in there is probably

  2. James Arthur

    James Arthur Guest

    You might try looking for CRT driver transistors.

    Sanyo's 2sc4188seems to meet your requirements:
    Ic = 100mA
    Pc = 10W

    James Arthur
  3. Joerg

    Joerg Guest

    Yep, I was just about to post the same. Often it is cheaper and more
    practical to take a few video transistors in parallel instead of one
    expensive boutique version. They are really cheap. The BF series
    contains some as well.
  4. Benj

    Benj Guest

    Don't know how YOU would go about that but I'd look in my "secret"
    references and come up with

    ..1 Ic.

    The "answer" is an old set of data books. Back in the heyday of
    discrete transistors it was a subscription service. They no longer
    seem to exist and even a Google search turned up nothing. They were
    called D.A.T.A. Inc. And had volumes for Transisor, diodes, SCRs and
    many other things. The one I have is from 1978 so they aren't too up
    to date put often you can cross-reference to more modern parts.

    Someone REALLY needs to put the last version of those old books on the
  5. MCM is taking orders (for later delivery) for
    "subs" for Sanyo's 2SC4188 (200V 10W 150MHz) and
    for Toshiba's 2sc2238b (200V 25W 100MHz), and
    2sc1569 (300V 12.5W 100MHz), and for Matsushita -
    Panasonic's 2sc1819 (300V 15W 100MHz).

    Toshiba's 2sc2238 (160V 25W 100MHz) is in stock.
  6. We have quite a few extremely hard to find 2SC and similar ic's in stock

    Prices are far below anywhere else.

    Many thanks,

    Don Lancaster voice phone: (928)428-4073
    Synergetics 3860 West First Street Box 809 Thatcher, AZ 85552
    rss: email:

    Please visit my GURU's LAIR web site at
  7. Tim Williams

    Tim Williams Guest

    Digging through my parts box, I found exactly four 2SC1569's, which probably
    came from old TV video outputs. Why it isn't three or six, I don't know...
    300V, 0.15A, 12.5W (awfully low for a TO-220), 40 hFE, 100 fT.

    These sort of transistors seem to be hard to come by. Just what do they use
    for oscilloscope deflection, anyway? Er well, used to, anyway. I suppose
    they're almost all digital and sampled stuff *these* days... but back in the
    old days they needed *something* good for hundreds of MHz bandwidth and
    hundreds of volts deflection. I can imagine pentodes doing that, or even a
    distributed amp, but there's only one tube in my Tek 475.

    Speaking of HF transistors, would you happen to have SRF397 in your records
    anywhere? Also, PT4576 or PT4578, CA2206, SS4556, etc. I've pulled a bunch
    of RF types that don't seem to show up anywhere.


    P.S. I'm thinking of modding my Heathkit IO-103. I'm thinking either
    improve what's there (not much to say for it, as is..), rip it out for a
    bare X-Y display (raw CRT leads ran to the front panel, or with deflection
    amps of some bandwidth), or maybe try making a whole sampling 'scope. I
    must say it would be impressive to hike bandwidth from 10MHz to 1GHz.
  8. Winfield

    Winfield Guest

    I can send you the datasheet for the Toshiba 2sc1569,
    if you can't get it anywhere. According to the plots,
    this transistor has Cob of 7pF at 10 volts, dropping to
    5pF at 100V and 4pF at 300V. They don't mention Ccb,
    but you'd likely drive it with a low Z signal so that
    shouldn't matter.

    With a Tj 150C spec and Pc = 12.5W at Tc = 25C, you can
    calculate RthJC = 10C/W, to worry about your heatsink
    design. Keep the heatsink-to-ground capacitance down.

    p.s. The high thermal resistance is a necessary result
    of this part's very small die, which is necessary to get
    the low capacitance you're counting on for a video amp.
  9. Tim Williams

    Tim Williams Guest

    I've found it at DatasheetArchive, but thanks anyway.
    Yeah, I was thinking cascode, or an emitter follower driver (that is to say,
    almost a darlington, with excessive E1-GND quiescent current available).

    I may've puttered around with this transistor before, or at least one like
    it. No, the one I was messing with was TO-202 and housemarked, that's
    right. In any case, it showed a nasty slowdown under, say, 30V, as if
    saturation voltage was just horrendous. I see on this datasheet that hFE is
    good (>50 typ. @ 25C, 1-100mA Ic), but I also see that it drops madly with
    Vce on the Ic-Vce plot. It looks like a fricking pentode! Is this a result
    of the small die's resistance?
    Original in the HK scope are D40N1 transistors, which are merely 50MHz, but
    3pF @ 20Vcb, half that of the C1569. I guess the moral is I get to kick up
    quiescent current a good bit. Oh, we were talking about heatsinks -- they
    mounted them to live heatsinks in open air, which is more or less okay
    because the chassis is pretty open, but will nonetheless add a few pF.
    Ah, true. I feel weird actually running transistors at their's
    almost like I'm using tubes here...

  10. Phil Hobbs

    Phil Hobbs Guest

    Good luck getting 1 GHz without a travelling-wave deflection structure
    in the tube.


    Phil Hobbs
  11. JosephKK

    JosephKK Guest

    Tim Williams posted to
    Along the way the changes in o'scope CRT deflection went from simple
    parallel plates to distributed deflection. This added quite a bit to
    the capacitance but improved the deflection sensitivity from many
    (tens of) volts per inch to (many tens of) millivolts per inch. This
    reduced the required magnitude of deflection voltage to fast
    transistor range. Trying to speed up a HV deflection amplifier
    without resorting to ultrafast HV FET's may be impractical.
  12. Tim Williams

    Tim Williams Guest

    Reminds me, I think I read in my Tek475's manual something about multiple
    deflection. The CRT has a number of pins along it.

    And that leads to another question ;-) -- would there be any value in
    MOSFETs for this? Probably cascoded, so the biasing is still handled by a
    nice and fast transistor. RLC of the gate is the ultimate roadblock, isn't
    it? Could still be pushed harder with excessive drive current, which I
    don't really have much of a problem with, as I have a few fast, ampy
    transistors on hand.

    If you meant JFETs, where do you find JFETs at more than 30V, 10mA and TO-18
    / TO-92 / etc., anyway? JFETs are so unpopular, it's not fair! (Checking
    Digikey, I see no more than 55V or 50mA -- 500mA is mentioned but it's got
    to be a Fairchild typo.)

  13. I don't know in particular, but check Interfet. High I is hard to
    come by in a JFET (among other things).

    greater than 100V, but low I:
  14. JosephKK

    JosephKK Guest

    Tim Williams posted to
    I suspect that would be a tradeoff, complexity versus cost.
    Then, no. Now yes. Some of the specs for wideband and SHF mosfets
    today are spectacular compared Tek 475 vintage.
    Nothing wrong with that. Just remember that as speed continues to
    increase, volts as well as volts/naonsecond matter to handle L issues
    in a small fractions of an inch.
    Unpopular? They are very useful and popular in tuners and UHF/SHF/EHF
    front ends, just not so much elsewhere anymore.
  15. Winfield

    Winfield Guest

    No, not so hard. You find these by looking for low Ron
    JFETs, which happen to also have very high Idss. An
    example is the J105, with Rds < 3 ohms and Idss = 500mA.
    It's available in TO-92, sot-223 (JFTJ105) packages.

    But note, for linear use one wouldn't be likely to use
    a possible-high operating current, like 500mA, unless
    Vds was awkwardly low, because the die would overheat.
    However we certainly do use large-die JFETs in linear
    appliations, namely low-noise amplifiers, because they
    have very low e_n. Then we set Id = 5mA or 10mA, etc.
  16. MooseFET

    MooseFET Guest

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