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led or zenon ?

Discussion in 'Electronic Design' started by colin, Mar 12, 2007.

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  1. colin

    colin Guest

    can a LED be as good as zenon for a strobe ?
    I need it bright enough to see well enough to balance a shaft at 5krpm or

    LED is so much simpler, I have one hooked up to the motor controller pic
    with just a 2n7002,
    it works enough to see the motor phase change,
    but it was just the white led from a cigar sized laser pointer/led torch.
    but cant realy see much if have the lights on.

    maybe a laser is the way to go ?

    how much power will a 5mw laser from such a device cope with in 50us bursts
    Im not too woried if it fails after a day or two of continuos use.
    Ive got some blown ones anyway maybe I should try one of those.

    Colin =^.^=
  2. D from BC

    D from BC Guest

    I think I read somewhere that white LED's are being used as camera
    flashes.. Maybe find that LED type..

    Assuming there's no laser specs available....
    I say get that 5mW laser nice and toasty.
    Sometimes destructive testing can yield faster results..
    On average isn't the destructive junction temp of most semiconductors
    somewhere around 100C?
    With that in mind, monitor the laser temperature to get an estimate of
    the junction temp.
    I have a laser level that uses a lens to project a line. Some sort of
    beam splitter I guess..
    There is no rotating mirror.
    Trivia: What's that lens called?
    D from BC
  3. colin

    colin Guest

    do you mean a fresnel lense? only one I can think of with a fancy name.

    the problem here is that diode lasers have an incredibly high power density
    at the optical surface and this can burn a hole in itself. with most lasers
    ive used theres a fine line between lasing and destruction, many have
    crossed this line !
    for pulse mode I gues its the thermal mass of the surface. but I dont know
    what this is, the specs on pointer type lasers is ... wel it isnt.

    Colin =^.^=
  4. colin

    colin Guest

    Its like xenon I think, and you dont get any x rays from this stuff, just z
    maybe its the next one along in the table ?
  5. Adnan Kurt

    Adnan Kurt Guest


    Unfortunately, it is not possible to achieve the photon flux of a
    flashlamp with regular solid state sources. And you will notice the
    fact with the LED flashes replaced by xenon flashlamps in high end
    cell phones.

    Well, typically (as an example), a xenon flashlamp in a stroboscope
    would utilize about 200mJ of electrical energy to generate photons for
    10s of microseconds. That is equal to 10s of kilowatts for a
    rectangular current pulse. That means, in order to have similar
    qualities (illumination, time window/ precision) you have to get
    kilowatt range of optical power from an LED for 10s of microseconds.
    To my knowledge, it is not possible to achieve corresponding
    luminosity for brief flashes using LEDs yet. With semiconductor
    lasers, it is the same problem. Even with very high power QCW laser
    arrays from Thales for example, you can get max 100W peak (140A
    maximum with a diode drop of <2V) and you can have it pulsed for us to
    ms range.

    Hope it will have some use.
  6. colin

    colin Guest

    Thanks for the input, I hadnt given it too much thought other than id need
    on average maybe a few watts of power at typical efficiencies, ie equal to a
    small torch,
    and at 166hz a 50us pulse is short enough to freeze motion quite well, wich
    is about 1%, so the peak power is about 100 times the average.
    certainly the leds I used were not particularly bright at all I just hit
    them with 5v via 1ohm rdson of the mosfet wich is probably quite serious

    The 1W devices are presumably a lot brighter, but theyr not cheap enought to
    use a whole bunch of them, especialy if theyr being abused like this.

    I gues you cant beat a xenon tube, I wonder if you could focus all that
    energy down to a point, that would be interesting.

    Colin =^.^=
  7. Palinurus

    Palinurus Guest

    Nope. Could be a cylinder lens (cheap) or a special laser line lens,
    which has a better light distribution (which might not matter in your
    application) but is relatively expensive.
    There are also holograms which achieve much the same effect. Think of
    the "pattern generators" available with super-cheap lasers.

    Many's the time I've wished for a simple square grid, or ring-and-dot
    pattern, but that would be too useful, too easy.

    As to the strobe business, I've seen a lot of LED strobe circuits, so
    it could work. Again, it depends on your conditions.
  8. colin

    colin Guest

    Yes ive seen a few led circuits, mine is desperatly simple as the PIC motor
    controler just drives a mosfet at a certain phase angle, I didnt even bother
    with a current limiting resistor just let the mosfet and diode battle it out
    with the full 5v, as it was only on for 50us at 166hz, there is about .6v
    vds drop accross the 2n7002 driven with 3.6vgs. makes it a bit uncertain as
    to exactly what the current is, but in the region of an amp, with 2 leds in
    parallel, the third one doesnt seem to work, but i had it in backwards to
    start with, probably the reverse 5v killed it.

    I was realy hoping someone who had use an led one could say if you can
    easily see the shaft stopped in motion with say a bunch of cheap leds even
    in good light or wether even with expensive ones its stil to dim unless u
    turn all the lights out.

    So I cant make my mind up wether to order some leds or a xenon tube, and
    make a hv inverter and trigger xfmr etc.

    I gues I should at least get a bunch of brighter leds and try it.
    any recomendations for bright leds with realy good performance/cost ?
    prefereably white ofc.

    If you want to know about laser filters you could ask on alt.lasers they
    know all sorts of stuff like that there, in fact one or two people visit
    here from time to time, I hang out there for a while while I was trying to
    strangle a diode laser with 2ghz for my heterodyne distance measurer, also
    had an interesting discusion about
  9. Guest

    Remember that if you pulse the LED, you can use more current, hence
  10. colin

    colin Guest

    well a strobe is pulsed by nature, 1% duty cycle seems to be ok to see the
    motion stopped without to much blur, so a 20ma avg would relate to 2amp
    pulsed, but I would imagine the efficieny falls off long before 2amps with a
    20ma diode.

    Colin =^.^=
  11. krw

    krw Guest

    It doesn't work that way. The eye averages light intensity and LEDs
    efficiency falls off at high power (note that the voltage goes up) so
    pulsing them at higher rate than the critical fusion frequency is a
    net loss.
  12. Guest

    The eye retains the peak intensity. It doesn't average. HP has a good
    ap note on this, though it's quite old. I couldn't find it on line.
    Though the effect is well known, Maurice Kanbar (Skyy Vodka inventor)
    managed to get a patent (5850126) on it.
  13. joseph2k

    joseph2k Guest

    Please note that white LEDs use a phosphor, this limits their rate to about
    1000 flashes per second max. It is the phosphor that is the limit.
    Non-phosphor LEDs go to MHz rather easily.
  14. RHRRC

    RHRRC Guest

  15. Guest

  16. RHRRC

    RHRRC Guest

  17. Guest

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