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Modern Transistor for Avalanche in SMT

Discussion in 'Electronic Design' started by Owen Roberts, Oct 8, 2012.

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  1. Owen Roberts

    Owen Roberts Guest

    Ok, I'm tired of hunting old mesa transistors on Ebay for pulse
    generators. I also want to get my loop area down to shorten the pulse.
    Anyone have a SMT part that is available at Digikey or Mouser that
    avalanches well?
    Say 3$ a unit max? Only other requirement is a packaging that a 40
    year old pair of eyes can handle.

    I know about the $14 to 20$ Zetex/Diodes Inc parts.

    Thanks,

    Steve
     
  2. Guest

    The old standard was 2n2369. I've also used 2n2222, I think it was.
    I tested a bunch of varieties. I'd have to dig through old notes.

    I got pretty good yields, but today you might as well use ordinary
    logic. It's faster, cheaper, easier, and makes better pulses. Unless
    you're trying to make amps, that is.
     
  3. Jeroen

    Jeroen Guest

    I've seen the BFG541 avalanche nicely, albeit at a somewhat
    lower voltage than a 2n2369. It's faster too.

    Jeroen Belleman
     
  4. Owen Roberts

    Owen Roberts Guest

    We have a little informal contest here on campus for fastest hand made
    pulser under 20$. Right now I'm loosing to the EE Dept's tech by 50
    pS.
    He had time during the summer to hand select devices. Only avalanche
    and SRD is allowed.

    Why Else? Convenience....

    I use pulsers like this in a ultrafast laser lab for testing
    photodetectors. They drive 1.3 micron VECSELs with a little bias
    network. Since the budget has to came out of my own pocket, I like
    the simplicity. I can build them dead bug.

    While no where near as fast as a femtosecond laser, its good enough
    to see if the PD is still good, if the termination is correct etc.

    Steve
     
  5. Tim Williams

    Tim Williams Guest

    I've always found 2N3904s work well, surprising for an epitaxial. Fast
    and RF transistors tend to work as well. Jim Williams was fond of the
    2N2369, as suggested; I've avalanched a, I think it was 2SA1016 (if I have
    that wrong, it's a nearby number, with specs something like 20V, 100mA, fT
    Tim
     
  6. Jamie

    Jamie Guest

    I posted a Ltspice using LT1720 (fast comparator) that can generate a
    15nS pulse, variable up to 250nS. It uses an inductor on the (+) input
    as the time constant (500uh). Input generator set to match what a
    Cmos version of the 555 timer can do on the raise and full time to
    trigger an interval.

    I wonder how a HEMT would do for you?

    Jamie
     
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